Myers Tenth - Chapter 2: The Biology of Mind
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In 2000, a Virginia teacher began collecting sex magazines, visiting child pornography websites, and then making subtle advances on his young stepdaughter. When his wife called the police, he was arrested and later convicted of child molestation. Though put into a sexual addiction rehabilitation program, he still felt overwhelmed by his sexual urges. The day before being sentenced to prison, he went to his local emergency room complaining of a headache and thoughts of suicide. He was also distraught over his uncontrollable impulses, which led him to proposition nurses.


A brain scan located the problem - in his mind's biology. Behind his right temple there was an egg-sized brain tumor. After surgeons removed the tumor, his lewd impulses faded and he returned home to his wife and stepdaughter. Alas, a year later the tumor partially grew back, and with it the sexual urges. A second tumor removal again lessened the urges (Burns & Swerdlow, 2003).

This case illustrates what you likely believe: that you reside in your head. If surgeons transplanted all your organs below your neck, and even your skin and limbs, you would (Yes?) still be you.

An acquaintance of mine received a new heart from a woman who, in a rare operation, required a matched heart-lung transplant. When the two chanced to meet in their hospital ward, she introduced herself: "I think you have my heart. "But only her heart. Her self, she assumed, still resided inside her skull. We rightly presume that our brain enables our mind. Indeed, no principle is more central in today's psychology, or to this book than this: Everything psychological is simultaneously biological.

Biology Behavior And Mind

Why are psychologists concerned with Biology?


Your every idea, every mood, every urge is a biological happening. You love, laugh, and cry with your body. Without your body - your genes, your brain, your appearance - you would indeed be nobody. Although we find it convenient to talk separately of biological and psychological influences on behavior, we need to remember: To think, feel, or act without a body would be like running without legs.

Our understanding of how the brain gives birth to the mind has come a long way. The ancient Greek philosopher Plato correctly located the mind in the spherical head - his idea of the perfect form. His student, Aristotle, believed the mind was in the heart, which pumps warmth and vitalitiy to the body. The heart remains our symbol for love, but science has long since overtaken philosophy on this issue. It's your brain, not your heart, that falls in love.

In the early 1800s, German physician Franz Gall proposed that phrenology, studying bumps on the skull, could reveal a person's mental abilities and character traits (Figure 2.1). At one point, Britain had 29 phrenological societies, and phrenologists traveled North America giving skull readings (Hunt, 1993). Using a false name, humorist Mark Twain put one famous phrenologist to the test. "He found a cavity [and] startled me by saying that that cavity represented the total absence of the sense of humor!"

Three months later, Twain sat for a second reading, this time identifying himself. Now "the cavity was gone, and in its place was...the loftiest bump of humor he had ever encountered in his life-long experience!" (Lopez 2002). Although its initial popularity faded, phrenology succeeded in focusing attention on the localization of function-the idea that various brain regions have particular functions.


A wrongheaded theory
Despite initial acceptance of Franz Gall's speculations, bumps on the skull tell us nothing about the brain's underlying functions. Nevertheless, some of his assumptions have held true. Though they are not the functions Gall proposed, different parts of the brain do control different aspects of behavior, as suggested here (from The Human Brain Book) and as you will see throughout this chapter.

You and I live in a time Gall could only dream about. By studying the links between biological activity and psychological events, those working from the biological perspective are announcing discoveries about the interplay of our biology and our behavior and mind at an exhiliarating pace. Within little more than the past century, researchers seeking to understand the biology of the mind have discovered that:

  • the body is composed of cells

  • among these are nerve cells that conduct electricity and "talk"

  • to one another by sending chemical messages across a tiny gap that separates them.

  • specific brain systems serve specific functions (though not the functions Gall supposed).

  • we integrate information processed in these different brain systems to construct our

  • experience of sights and sounds, meanings and memories, pain and passion.

  • our adaptive brain is wired by experience.

We have also realized that we are each a system composed of subsystems that are in turn composed of even smaller subsystems. Tiny cells organize to form body organs. These organs form larger systems for digestion, circulation, and information processing. And those systems are part of an even larger system - the individual, who in turn is a part of a family, culture, and community. Thus, we are biopsychosocial systems. To understand our behavior, we need to study how these biological, psychological, and social systems work and interact.

"If I were a college student today, I don't think I could resist going into neuroscience."

Novelist Tom Wolfe, 2004

In this book we start small and build from the bottom up - from nerve cells up to the brain in this chapter, and to the environmental influences that interact with our biology in later chapters. We will also work from the top down, as we consider how our thinking and emotions influence our brain and our health.

Retrieval Practice
  • What do phrenology and psychology's biological perspective have in common?

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Neural Communications

For scientists, it is a happy fact of nature that the information systems of humans and other animals operate similarly - so similarly that you could not distinguish between small samples of brain tissue from a human and a monkey. This similarity allows researchers to study relatively simple animals, such as squids and sea slugs, to discover how our neural systems operate. It allows them to study other mammal's brains to understand the organization of our own. Cars differ, but all have engines, accelerators, steering wheels, and brakes. A Martian could study any one of them and grasp the operating principles. Likewise, animals differ, yet their nervous systems operate similarly. Though the human brain is more complex than a rat's, both follow the same principles.


2-2: What are Neurons and how do they communicate

biological perspective      concerned with the links between biology and behavior. Includes psychologists working in neuroscience, behavior genetics, and evolutionary psychology. These researchers may call themselves behavioral neuroscientists, neuropsychologists, behavior geneticists, physiological psychologists, or biopsychologists.

neuron      a nerve cell; the basic building block of the nervous system.

dendrites      a neuron's bushy, branching extensions that receive messages and conduct impulses toward the cell body.

axon      the neuron extension that passes messages through its branches to other neurons or to muscles or glands.

myelin[MY-uh-lin] sheath      a fatty tissue layer segmentally encasing the axons of some neurons; enables vastly greater transmission speed as neural impulses hop from one node to the next.

Our body's neural information system is complexity built from simplicity. Its building blocks are neurons, or nerve cells. To fathom our thoughts and actions, memories and moods, we must first understand how neurons work and communicate.

Neurons differ, but all are variations on the same theme (Figure 2.2). Each consists of a cell body and its branching fibers. The bushy dendrite fibers receive information and conduct it toward the cell body. From there, the cell's lengthy axon fiber passes the message through its terminal branches to other neurons or to muscles or glands. Dendrites listen. Axons speak.

Unlike the short dendrites, axons may be very long, projecting several feet through the body. A neuron carrying orders to a leg muscle, for example, has a cell body and axon roughly on the scale of a basketball attached to a rope 4 miles long. Much as home electrical wire is insulated, some axons are encased in a myelin sheath, a layer of fatty tissue that insulates them and speeds their impulses. As myelin is laid down up to about age 25, neural efficiency, judgment, and self-control grows (Fields, 2008). If the myelin sheath degenerates, multiple sclerosis results: Communication to the muscles slows, with eventual loss of muscle control.

Neurons transmit messages when stimulated by signals from our senses or when triggered by chemicals from neighboring neurons. In response, a neuron fires an impulse, called the action potential-a brief electrical charge that travels down its axon.


"I sing the body electric."

Walt Whitman Children of Adam (1855)

Depending on the type of fiber, a neural impulse travels at speeds ranging from a sluggish 2 miles per hour to a breakneck 180 miles per hour. But even this top speed is 3 million times slower than that of electricity through a wire. We measure brain activity in milliseconds (thousandths of a second) and computer activity in nanoseconds (billionths of a second). Thus, unlike the nearly instantaneous reactions of a high-speed computer, your reaction to a sudden event, such as a child darting in front of your car, may take a quarter-second or more. Your brain is vastly more complex that a computer, but slower at executing simple response. And if you are an elephant - whose round-trip message travel time from a yank on the tail to the brain and back to thte tail is 100 times longer than for a tiny shrew - reflexes are slower yet (More et al., 2010).

Like batteries, neurons generate electricity from chemical events. In the neuron's chemistry-to-electricity process, ions (electrically charged atoms) are exchanged. The fluid outside an axon's membrane has mostly positively charged ions; a resting axon's fluid interior has mostly negatively charged ions. This positive-outside/negative-inside state is called the resting potential. Like a tightly guarded facility, the axon's surface is very selective about what it allows through its gates. We say the axon's surface is selectively permeable.

When a neuron fires, however, the security parameters change: The first section of the axon opens its gates, rather like sewer covers flipping open, and positively charged sodium ions flood through the cell membranes (Figure 2.3). This depolarizes that axon section, causing another axon channel to open, and then another, like a line of falling dominos, each tripping the next.


During a resting pause (the refractory period, rather like a web page pausing to refresh), the neuron pumps the positively charged sodium ions back outside. Then it can fire again. (In myelinated neurons, as in Figure 2.2, the action potential speeds up by hopping from the end of one myelin sausage to the next.) The mind boggles when imagining this electrochemical process repeating up to 100 or even 1000 times a second. But this is just the first of many astonishments.

action potential      a neural impulse; a brief electrical charge that travels down an axon.

threshold      the level of stimulation required to trigger a neural impulse

Each neuron is itself a miniature decision-making device performing complex calculations as it receives signals from hundreds, even thousands of other neurons. Most signals are excitatory, somewhat like pushing a neuron's accelerator. Some are inhibitory, more like pushing its brake. If excitatory signals minus inhibitory signals exceed a minimum intensity, or threshold, the combined signals trigger an action potential. (Think of it this way: If the excitatory party animals outvote the inhibitory party poopers, the party's on.) The action potential then travels down the axon, which branches into junctions with hundreds or thousands of other neurons or with the body's muscles and glands.

Retrieval Practice
  • When a neuron fires an action potential, the information travels through the axon, the dendrites, and the axon’s terminal branches, but not in that order. Place these 3 structures in the correct order.

  • How does our nervous system allow us to experience the difference between a slap and a tap on the back?

How Neurons Communicate

2-3: How do nerve cells communicate with other nerve cells

Neurons interweave so intricately that even with a microscope you would have trouble seeing where one neuron ends and another begins. Scientists once believed that the axon of one cell fused with the dendrites of another in an uninterrupted fabric. Then British physiologist Sir Charles Sherrington (1857 - 1952) noticed that neural impulses were taking an unexpectedly long time to travel a neural pathway. Inferring that there must be a brief interruption in the transmission, Sherrington called the meeting point between neurons a synapse.


We now know that the axon terminal of one neuron is in fact separated from the receiving neuron by a synaptic gap (or synaptic cleft) of less than a millionth of an inch wide. Spanish anatomist Santiago RamÓn y Cajal (1852 - 1934) marveled at these near-unions of neurons, calling them protoplasmic kisses. Like elegant ladies air-kissing so as not to muss their makeup, dendrites and axons don't quite touch, notes poet Diane Ackerman (2004). How do the neurons execute this protoplasmic kiss, sending information across the tiny synaptic gap? the answer is one of the important scientific discoveries of our age.

"All information processing in the brain involves neurons 'talking to' each other at synapses."

Neuroscientist Solomon H. Snyder (1984)

When an action potential reaches the knoblike terminals at an axon's end, it triggers the release of chemical messengers, called neurotransmitters (Figure 2.4). Within 1/10,000th of a second, the neurotransmitter molecules cross the synaptic gap and bind to receptor sites onthe receiving neuron - as precisely as a key fits a lock. For an instant, the neurotransmitter unlocks tiny channels at the receiving site, and electrically charged atoms flow in, exciting or inhibiting the receiving neuron's readiness to fire. Then, in a process called reuptake, the sending neuron reabsorbs the excess neurotransmitters.

Retrieval Practice
  • What happens in the synaptic gap?

  • What is reuptake?

How Neurotransmitters Influence Us

2-4: How do neurostransmitters influence behavior, and how do drugs and other chemicals affect neurotransmission?

In their quest to understand neural communication, researchers have discovered dozens of different neurotransmitters and almost as many new questions: Are certain neurotransmitters found only in specific places? How do they affect our moods, memories, and mental abilities?Can we boost or diminish these effects through drugs or diet?

"When it comes to the brain, if you want to see the action, follow the neurotransmitters."

Neuroscientist Floyd Bloom (1993)


Figure 2.5
Neurotransmitter Pathways
Each of the brain’s differing chemical messengers has designated pathways where it operates, as shown here for serotonin and dopamine (Carter 1998).

synapse  [SIN-aps]    the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or synaptic cleft.

neurotransmitters      chemical messengers that cross the synaptic gaps between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse.

reuptake      a neurotransmitter’s reabsorption by the sending neuron.

Later chapters explore neurotransmitter influences on hunger and thinkin, depression and euphoria, addictions and therapy. A particular brain pathway may use only one or two neurotransmitters (FIGURE 2.5), and particular neurotransmitters may affect specific behaviors and emotions(TABLE 2.1). But neurotransmitter systems don't operate in isolation; they interact, and their effects vary with the receptors the stimulate. Acetylcholine (ACh), which plays a role in learning and memory, is one of the best-understood neurotransmitters. In addition, it is the messenger at every junction between motor neurons (which carry information from the brain and spinal cord to the body’s tissues) and skeletal muscles. When ACh is released to our muscle cell receptors, the muscle contracts. If ACh transmission is blocked, as happens during some kinds of anesthesia, the muscles cannot contract and we are paralyzed.

Candace Pert and Solomon Snyder (1973) made an exciting discovery about neurotransmitters when they attached a radioactive tracer to morphine, showing where it was taken up in an animal’s brain. The morphine, an opiate drug that elevates mood and eases pain, bound to receptors in areas linked with mood and pain sensations. But why would the brain have these "opiate receptors"?Why would it have a chemical lock, unless it also had a natural key to open it?


Researchers soon confirmed that the brain does indeed produce its own naturally occuring opiates. Our body releases several types of neurostransmitter molecules similar to morphine in response to pain and vigorous exercise. These endorphins (short for endogenous [produced within] morphine) help explain good feelings such as the "runner’s high,"the painkilling effects of acupuncture, and the indifference to pain in some severely injured people. But once again, new knowledge led to new questions.

"Physician Lewis Thomas, on the endorphins: 'There it is, a biologically universal act of mercy. I cannot explain it, except to say that I would have put it in had I been around at the very beginning, sitting as a member of the planning committee.'"

The Youngest Science, 1983

Retrieval Practice
  • Serotonin, dopamine, and endorphins are all chemical messengers called ________

How Drugs and Other Chemicals Alter Neurotransmission

If indeed the endorphins lessen pain and boost mood, why not flood the brain with artificial opiates, thereby intensifying the brain’s own "feel-good" chemistry? One problem is that when flooded with opiate drugs such as heroin and morphine, the brain may stop producing its own natural opiates. When the drug is withdrawn, the brain may then be deprived of any form of opiate, causing intense discomfort. For suppressing the body’s own neurotransmitter production, nature charges a price.

endorphins  [en-DOR-fins]    "morphine within" - natural, opiatelike neurotransmitters linked to pain control and pleasure.

neurotransmitters      chemical messengers that cross the synaptic gaps between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse.

reuptake      a neurotransmitter’s reabsorption by the sending neuron.

Drugs and other chemicals affect brain chemistry at synapses, often by either exciting or inhibiting neurons’ firing. Agonist molecules may be similar enough to a neurotransmitter to bind to its receptor and mimic its effects. Some opiate drugs area agonists and produce a temporary "high" by amplifying normal sensations and pleasure.

Antagonists also bind to receptors but their effect is instead to block a neurotranmitter’s functioning.

Retrieval Practice
  • Curare poisoning paralyzes its victims by blocking ACh receptors involved in muscle movements. Morphine mimics endorphin actions. Which is agonist, and which is the antagonist?


Figure 2.6
Agonists and Antagonists
Agonists mimic neurotransmitters, Antagonists block neurotransmitter action.

Botulin, a poison that can form in improperly canned food, causes paralysis by blocking ACh release. (Small injections of botulin - Botox - smooth wrinkles by paralyzing the underlying facial muscles.) These antagonists are enough like the natural neurotransmitter to occupy its receptor site and block its effect, as in FIGURE 2.6, but are not similar enough to stimulate the receptor (rather like foreign coins that fit into, but will not operate, a candy machine). Curare, a poison some South American Indians have applied to hunting-dart tips, occupies and blocks ACh receptor sites on muscles, producing paralysis in animals struck by the darts.

The Nervous System

2-5: What are the function of the nervous system’s main divisions, and what are the 3 main types of neurons?

nervous system      the body’s speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous systems.

central nervous system (CNS)      the brain and spinal cord.

To live is to take in information from the world and the body’s tissues, to make decisions, and to send back information and orders to the body’s tissues. All this happens thanks to our body’s nervous system ( FIGURE 2.7). The brain and spinal cord form the central nervous system (CNS), the body’s decision maker. The peripheral nervous system (PNS) is responsible for gathering information and for transmitting CNS decisions to other body parts. Nerves, electrical cables formed of bundles of axons, link the CNS with the body’s sensory receptors, muscles, and glands. The optic nerve, for example, bundles a million axons into a single cable carrying the messages each eye sends to the brain (Mason & Kandel, 1991).


peripheral nervous system (PNS)      the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body.

nerves      bundled axons that form neural "cables" connecting the central nervous system with muscles, glands, and sense organs.

Information travels in the nervous system though three types of neurons. Sensory neurons carry messages from the body’s tissues and sensory receptors inward to the brain and spinal cord for processing. Motor neurons carry instructions from the central nervous system out to the body’s muscles. Between the sensory input and motor output, information is processed in the brain’s internal communication system via its interneurons. Our complexity resides mostly in our interneuron systems. Our nervous system has a few million sensory neurons, a few million motor neurons, and billions and billions of interneurons.

Peripheral Nervous System

sensory neurons      neurons that carry incoming information from the sensory receptors to the brain and spinal cord.

motor neurons      neurons that carry outgoing information from the brain and spinal cord to the muscles and glands.

interneurons      neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs.

somatic nervous system      the division of the peripheral nervous system that controls the body’s skeletal muscles. Also called the skeletal nervous system.

autonomic  [aw-tuh-NAHM-ik]  nervous system (ANS)  the part of the peripheral nervous system that controls the glands and the muscles of the internal organs (such as the heart);. Its sympathetic division arouses; its parasympathetic division calms.

Our peripheral nervous system has two components - somatic and autonomic. Our somatic nervous system enables voluntary control of our skeletal muscles. As you reach the end of the page, your somatic nervous system will report to your brain the current state of your skeletal muscles and carry instructions back, triggering your hand to select the next section.

Our autonomic nervous system (ANS) controls our glands and the muscles of our internal organs, influencing such activity as glandular activity, hearbeat, and digestion. Like an automatic pilot, this system may be consciously overridden, but usually operates on its own (autonomously).

The autonomic nervous system serves two important basic functions (FIGURE 2.8). The sympathetic nervous system arouses and expends energy. if something alarms or challenges you (such as a longed-for job interview), your sympathetic nervous system will accelerate your heartbeat, slow your digestion, raise your blood sugar, and cool you with perspiration, making you alert and ready for action. When the stress subsides (the interview is over), your parasympathetic nervous system will produce the opposite effects, conserving energy as it calms you by decreasing your heartbeat, lowering your blood sugar, and so forth. In everyday situations, the sympathetic and parasympathetic nervous systems work together to keep you in a steady internal state.


Figure 2.8
The dual functions of the autonomic nervous system
The autonomic nervous system controls the more autonomous (or self-regulating) internal functions. Its sympathetic division arouses and expends energy. Its parasympathetic division calms and conserves energy, allowing routine maintenance activity. For example, sympathetic stimulation accelerates heartbeat, whereas parasympathetic stimulation slows it.

sympathetic nervous system      the division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations.

parasympathetic nervous system      the division of the autonomic nervous system tha calms the body, conserving its energy.

I recently experienced my ANS in action. Before sending me into an MRI machine for a routine shoulder scan, the technician asked if I had issues with claustrophobia. "No, I am fine, " I assured her, with perhaps a hint of macho swagger. Moments later, as I found myself on my back, stuck deep inside a coffin-sized box and unable to move, my sympathetic nervous system had a different idea. As claustrophobia overtook me, my heart began pounding and I felt a desperate urge to escape. Just as I was about to cry for release, I suddenly felt my calming parasympathetic nervous system kick in. My heart rate slowed and my body relaxed, though my arousal surged again before the 20-minute confinement ended. "You did well!" the technician said, unaware of my ANS roller coaster ride.

Retrieval Practice
  • Match the type of neuron to its description

    1. Motor Neurons  a. carry incoming messages from sensory recptors to the CNS
    2. Sensory Neurons  b. communicate within the CNS and intervene between incoming and outgoing messages.
    3. Interneurons  c. carry outing messages form the CNS to muscles and glands

  • What bodily changes does your autonomic nervous system (ANS) direct before and after you give an important speech?

Central Nervous System

Form the simplicity of neurons "talking" to other neurons arises the complexity of the central nervous system’s brain and spinal cord.

It is the brain that enables our humanity - our thinking, feeling, and acting. Tens of billions of neurons, each communicating with thousands of other neurons, yield an everchanging wiring diagram. With some 40 billion neurons, each connecting with roughly 10,000 other neurons, we end up with perhaps 400 trillion synapses - places where neurons meet and greet their neighbors (deCourten-Myers, 2005). A grain-of-sand sized speck of your brain contains some 100,000 neurons and 1 billion "talking" synapses (Ramachandran & Blakeslee, 1998).

The brain’s neurons cluster intow work groups called neural networks. To understand why, Stephen Kosslyn and Olivier Koenig (1992, p. 12) have invited us to "think about why cities exist; why don’t people distribute themselves evenly across the countryside?"  Like people networking with other people, neurons network with nearby neurons with which they can have short, fast connections. As in FIGURE 2.9, each layer’s cells connect with various cells in the neural network’s next layer. Learning - to play the violin, speak a foreign language, sovle a math problem - occurs as feedback strengthens connections. Neurons that fire together wire together.


reflex      a simple, automatic response to a sensory stimulus, such as the "knee-jerk" response.

The other part of the CNS, the spinal cord, is a two-way information highway connecting between the peripheral nervous system and the brain. Ascending neural fibers send up sensory information, and descending fibers send back motor-control information. The neural pathways governing our reflexes, our automatic responses to stimuli, illustrate the spinal’s work. A simple spinal reflex is composed of a single sensory neuron and a single motor neuron. These ofen communicate through an interneuron. The knee-jerk response, for example, involves one such simple pathway. A headless warm body could do it.

Another such pathway is the pain reflex (FIGURE 2.10).when your finger touches a flame, neural activity (excited by the heat) travels via sensory neurons to interneurons in your spinal cord. The interneurons respond by activating motor neurons leading to the muscles in your arm. Because the simple pain-reflex pathway runs from the candle’s flame before your brain receives and responds to the information that causes you to feel pain. That’s why it feels as if your hand jerks away not by your choice, but on its own.


Information travels to and from the brain by way of the spinal cord. Were the top of your spinal cord severed, you would not feel pain from your body below. Nor would you feel pleasure. With your brain literally out of touch with your body, you would lose all sensation and voluntary movement in the body regions with sensory and motor connections to the spinal cord below its point of injury. You would exhibit the knee jerk without feeling the tap. When the brain center keeping the brakes on erections is severed, men paralyzed below the waist may be capable of an erection (a simple reflex) if their genitals are stimulated. (Goldstein, 2000). Women similarly paralyzed may respond with vaginal lubrication. But, depending on where and how completely the spinal cord is severed, they may be genitally unresponsive to erotic images and have no genital feeling (Kennedy & Over, 1990; Sipski & Alexander, 1999). To produce bodily pain or pleasure, the sensory information must reach the brain.

"If the nervous system be cut off between the brain and other parts, the experiences of those other parts are nonexistent for the mind. The eye is blind, the ear deaf, the hand insensible and motionless."

William James, Principles of Psychology, 1890

The Endocrine System

2-6: How does the endocrine system transmit information and interact with the nervous system?

endocrine  [EN-duh-krin]  system  the body’s "slow" chemical communication system; a set of glands that secrete hormones into the bloodstream.

hormones      chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues.

So far we have focused on the body’s speedy electrochemical information system. Interconnected with your nervous system is a second communication system, the endocrine system (FIGURE 2.11). The endocrine system’s glands secrete another form of chemical messengers, hormones, which travel through the bloodstream and affect other tissues, including the brain. When hormones act on the brain, they influence our interest in sex, food, and aggression.

Some hormones are chemically identical to neurotransmitters (the chemical messengers that diffuse across a synapse and excite or inhibit an adjacent neuron.) The endocrine system and nervous system are therefore close relatives: Both produce molecules that act on receptors elsewhere. Like many relatives, they also differ.The speedy nervous system zips messages from eyes to brain to hand in a fraction of a second. Endocrine messages trudge along in the bloodstream, taking several seconds or more to travel from the gland to the target tissue. If the nervous system’s communication delivers messages with the speed of a text message, the endocrine system is more like sending a letter.

But slow and steady sometimes wins the race. Endocrine messages tend to outlast the effects of neural messages. That helps explain why upset feelings may linger beyond our awareness of what upset us. When this happens, it takes time for us to "simmer down."In a moment of danger, for example, the ANS orders the adrenal glands on top of the kidneys to release epinephrine and norepinephrine (also called adrenaline and noradrenaline). These hormones increase heart rate, blood pressure, and blood sugar, providing us with a surge of energy. When the emergency passes, the hormones - and the feelings of excitement - linger a while.


adrenal  [ah-DREEN-el]  glands  a pair of endocrine glands that sit just above the kidneys and secrete hormones (epinephrine and norepinephrine) that help arous the body in times of stress.

pituitary gland      the endocrine system’s most influential gland. Under the influence of the hypothalamus, the pituitary regulates growth and controls other endocrine glands.

The most influential endocrine gland is the pituitary gland, a pea-sized structure located in the core of the brain, where it is controlled by an adjacent brain area, the hypothalamus (more on that shortly). The pituitary releases certain hormones. One is a growth hormone that stimulates physical development. Another, oxytocin, enables contractions associated with birthing, milk flow during nursing, and orgasm. Oxytocin also promotes a pair bonding, group cohesion, and social trust (De Dreu et al., 2010). During a laboratory game, those given a nasal squirt fo oxytocin rather than a placebo were more likely to trust strangers with their money (Kosfeld et al. 2005).

Pituitary secretions also influence the release of hormones by other endocrine glands. the pituitary, then, is a sort of master gland (whose own master is the hypothalamus). For example, under the brain’s influence, the pituitary triggers your sex glands to release sex hormones. These in turn influence your brain and behavior. So, too with stress. A stressful event triggers your hypothalamus to instruct your pituitary to release a hormone that causes your adrenal glands to flood your body with cortisol, a stress hormone that increases blood sugar.

This feedback system (brain ➠ pituitary ➠ other glands ➠ hormones ➠ body and brain) reveals the intimate connection of the nervous and endocrine systems. The nervous system directs endocrine secretions, which then affect the nervous system. Conducting and coordinating this whole electrochemical orchestra is the maestro we call the brain.

Retrieval Practice
  • Why is the pituitary gland called the "master gland"?

  • How are the nervous and endocrine systems alike, and how do they differ?

The Brain

In a jar on a display shelf in Cornell University’s psychology department resides the well-preserved brain of Edward Bradford Titchener, a late-nineteenth-century experimental psychologist and proponent of the study of consciousness. Imagine yourself gazing at that wrinkled mass of grayish tissue, wondering if in any sense Titchener is still in there.

You might answer that, without the living whir of electrochemical activity, there could be nothing of Titchener in his preserved brain. Consider, then, an experiment about which the inquisitive Titchener himself might have daydreamed. Imagine that just moments before his death, someone had removed Titchener’s brain and kept it alive by feeding it enriched blood. Further imagine that someone then transplanted the still-living brain into the body of a person whose own brain had been severely damaged. To whose home should the recovered patient return?


"I am a brain, Watson. The rest of me is a mere appendix."

Sherlock Holmes, in Arthur Conan Doyle’s "The Adventure of the Mazarin Stone"

That we can imagine such questions illustrates how convinced we are that we live "somewhere north of the neck"(Fodor, 1999). And for good reason: The brain enables the mind - seeing, hearing, smelling, feeling, remembering, thinking, speaking, dreaming. Moreover, it is the brain that self-reflectively analyzes the brain. When we’re thinking about our brain, we’re thinking with our brain - by firing across millions of synapses and releasing billions of neurotransmitter molecules. The effect of hormones on experiences such as love remind us that we would not be of the same mind if we were a bodiless brain. Brain + Body = Mind. Nevertheless, say neuroscientists, the mind is what the brain does. Brain, behavior, and cognition are an integrated whole. But precisely where and how are the mind’s functions tied to the brain? Let’s first see how scientists explore such questions.

Tools Of Dicovery

2-7: How do neuroscientists study the brain’s connections to behavior and mind.

A century ago, scientists had no tools high-powered yet gentle enough to explore the living human brain. Early clinical observations by physicians and others revealed some brain-mind connections. Damage to one side of the brain often caused numbness or paralysis in the body’s opposite side, suggesting that the body’s right side is wired to the brain’s left side, and vice versa. Damage to the back of the brain disrupted vision, and to the left-front part of the brain produced speech difficulties. Gradually, these explorers were mapping the brain.

lesion  [LEE-zhuhn]    tissue destruction. A brain lesion is a naturally or experimentally caused destruction of the brain tissue.

Now within a lifetime, a new generation of neural cartographers is probing and mapping the known universe’s most amazing organ. Scientists can selectively lesion (destroy) tiny clusters of brain cells, leaving the surrounding tissue unharmed. In the laboratory, such studies have revealed, for example, that damage to one area of the hypothalamus in a rat’s brain reduces eating, to the point of starvation, whereas damage in another area produces overeating.

Today’s neuroscientists can also electrically, chemically, or magnetically stimulate various parts of the brain and note the effect. Depending on the stimulated brain part, people may - to name a few examples - giggle, hear voices, turn their head, feel themselves falling, or have an out-of-body experience (Selimbyoglu & Parvizi, 2010). Scientists can even snoop on the messages of individual neurons. With tips so small they can detect the electrical pulse in a single neuron, modern microelectrodes can, for example, now detect exactly where the information in a cat’s brain when someone strokes its whisker. Researchers can also eavesdrop on the chatter of billions of neurons and can see color representations of the brain’s energy-consuming activity.


Minding Minds
Neuroscientists Hanna Damasio and Antonio Damasio explore how the brain makes mind.


Figure 2.12
An electroencephalograph providing amplified tracings of waves of electrical activity in the brain.

Right now, your mental activity is emitting telltale electrical, metabolic, and magnetic signals that would enabled neuroscientists to observe your brain at work. Electrical activity in your brain’s billions of neurons sweeps in regular waves across its surface. An ElectroEncephaloGram (EEG) is an amplified read-out of such waves. Researchers record the brain waves through a shower cap-like hat that is filled with electrodes covered with a conductive gel. Studying an EEG of the brain’s activity is like studying a car engine by listening to its hum. With no direct access to the brain, researches present a stimulus repeatedly and have the computer filter out brain activity unrelated to the stimulus. What remains is the electrical wave evoked by the stimulus (FIGURE 2.12).

"You must look into people, as well at them," advised Lord Chesterfield in a letter to his son. Unlike EEGs, newer neuroimaging techniques give us that Supermanlike abiltiy to see inside the living brain. One such tool, the PET (positron emission tomography) scan (FIGURE 2.13), depicts brain activity by showing each brain area’s consumption of its chemical fuel, the sugar glucose.Active neurons are glucose hogs, and after a person receives temporarily radioactive glucose, the PET scan can track the gamma rays released by this "food for thought" as the person performs a given task. Rather like a weather radar showing rain activity, PET scan "hot spots" show which brain areas are most active as the person does mathematical calculations, looks at images of faces, or daydreams.


The PET Scan
To obtain a PET scan, researchers inject volunteers with a low and harmless dose of short-lived radio-active sugar. Detectors around the person's head pick up the release of gamma rays from the sugar, which has concentrated in active brain areas. A computer then processes and translates these signals into a map of the brain at work.


MRI scan of a healthy individual (left) and a person with schizophrenia (right)
Note the enlarged ventricle, the fluid-filled brain region at the tip of the arrow in the image on the right.

In MRI (magnetic resonance imaging) brain scans, the person’s head is put in a strong magnetic field, which aligns the spinning atoms of brain molecules.Then a radio wave pulse momentarily disorients the atoms. When the atoms return to their normal spin, they emit signals that provide a detailed picture of soft tissues, including the brain. MRI scans have revealed a larger-than-average nerual area in the left hemisphere of musicians who display perfect pitch (Schlaug et al., 1995). They have also revealed enlarged ventricles - fluid-filled brain areas (marked by the red arrows in FIGURE 2.14) - in some patients who have schizophrenia, a disabling psychological disorder.

EEG (electroencephalogram)      an amplified recording of the waves of electrical activity that sweep across the brain’s surface.These waves are measured by electrodes placed on the scalp.

PET (positron emission tomography) scan      a visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task.

MRI (magnetic resonance imaging)      a technique that uses magnetic fields to produce computer-generated images of soft tissue. MRI scans show brain anatomy.

fMRI (functional MRI)      a technique for revealing bloodflow and, therefore, brain activity by comparing successive MRI scans. fMRI scans show brain function.

A special application of MRI - fMRI (functional MRI) - can reveal the brain’s functioning as well as its structure. Where the brain is especially active, blood goes. By comparing MRI scans taken less than a second apart, researchers can watch the brain "light up" (with increased oxygen-laden bloodflow) as a person performs different mental functions. As the person looks at a scene, for example, the fMRI machine detects blood rushing to the back of the brain, which processes visual information (see Figure 2.27, in the discussion of cortex functions).

Such snapshots of the brain’s changing activity are providing new insights - albeit sometimes overstated (Vul et al., 2009a,b) - into how the brain divides its labor. A mountain of recent fMRI studies suggest which brain areas are most active when people feel pain or rejection, listen to angry voices, think about scary things, feel happy, or become sexually excited. The technology enables a very crude sort of mind reading. After scanning 129 people’s brains as they did eight different mental tasks (such as reading, gambling, or rhyming), neruoscientists were able, with 80 percent accuracy, to predict which of these mental activities people were doing (Poldrack et al., 2009). Other studies have explored brain activity associated with religious experience, though without settling the question of whether the brain is producing or perceiving God (Fingelkurts & Fingelkurts, 2009; Inzlicht et al., 2009; Kapogiannis et al., 2009).

Today’s techniques for peering into the thinking, feeling brain are doing for psychology what the microscope did for biology and the telescope for astrnonomy. From them we have learned more about the brain in the last 30 years than in the previous 30,000. To be learning about the neurosciences now is like studying world geography while Magellan was exploring the seas. This truly is the golden age of brain science.

Retrieval Practice
  • Match the scanning technique with the correct description.

    1. fMRI scan  a. tracks radioactive glucose to reveal brain activity
    2. PET scan  b. tracks successive images of brain tissue to show brain function.
    3. MRI scan  c. uses magnetic fields and radio waves to show brain anatomy.

Older Brain Structures

2-8: What structures make up the brainstem, and what are the functions of the brainstem, thalamus, and cerebellum?

An animal’s capacities come from its brain structures. In primitive animals, such as sharks, a not-so-complex brain primarily regulates basic survival functions: breathing, resting, and feeding. In lower mammals, such as rodents, a mroe complex brain enables emotion and greater memory. In advanced mammals, such as humans, a brain that processes more information enables increased foresight as well.

This increasing complexity arises from new brain systems built on top of the old, much as the Earth's landscape covers the old with the new. Digging down, one discovers the fossil remnants of the past - brainstem components performing much as they did for our ancient ancestors. Let’s start with the brain’s basement and work up to the newer systems.


brainstem      the oldest part of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions.

medulla  [muh-DUL-uh]    the base of the brainstem; controls heartbeat and breathing.

The brain’s oldest and innermost region is the brainstem. It begins where the spinal cord swells slightly after entering the skull. This slight swelling is the medulla (FIGURE 2.15). Here lie the control for your heartbeat and breathing. The brainstem handles those tasks.

Just above the medulla sits the pons, which helps coordinate movements. If a cat’s brainstem is severed from the rest of the brain above it, the animal will still breathe and live - and even run, climb, and groom (Klemm, 1990). But cut off from the brain’s higher regions, it won’t purposefully run or climb to get food.

The brainstem and thalamus
The brainstem, including the pons and medulla, is an extension of the spinal cord. The thalamus is attached to the top of the brainstem. The reticular formation passes through both structures.


The brainstem is a crossover point, where most nerves to and from each side of the brain connect with the body’s opposite side (FIGURE 2.16). This peculiar cross-wiring is but one of the brain’s many surprises


The body’s wiring
Nerves from the left side of the brain are mostly linked to the right side of the body, and vice versa


thalamus  [THAL-uh-muss]    the brain’s sensory switchboard, located on top of the brainstem; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla.

Sitting atop the brainstem is the thalamus, a pair of egg-shaped structures that act as the brain’s sensory switchboard (Figure 2.15). The thalamus receives information from all the senses except smell and routes it to the higher brain regions that deal with seeing, hearing, and touching. The thalamus also receives some of the higher brain’s replies, which it then directs to the medulla and to the cerebellum (see below). Think of the thalamus as being to sensory information what London is to England’s trains: a hub through which traffic passes en route to various destinations.

Reticular Formation

reticular formation      a nerve network that travels through the brainstem and plays an important role in controlling arousal.

Inside the brainstem, between your ears, lies the reticular "netlike" formation, a finger-shaped network of neurons that extends from the spinal cord right up through the thalamus. As the spinal cord’s sensory input flows up to the thalamus, some of it travels through the reticular formation, which filters incoming stimuli and relays important information to other brain areas.

In 1949, Giuseppe Moruzzi and Horace Magoun discovered that electrically stimulating the reticular formation of a sleeping cat almost instantly produced an awake, alert animal. When Maguon severed a cat’s reticular formation without damaging the nearby sensory pathways, the effect was equally dramatic: The cat lapsed into a coma from which it never awakened. The conclusion? The reticular formation enables arousal.


Extending from the rear of the brainstem is the baseball-sized cerebellum, meaning "little brain," which is what its two wrinkled halves resemble (FIGURE 2.17). As you will see in Chapter 8, the cerebellum enables nonverbal learning and memory. It also helps us judge time, modulate our emotions, and discriminate sounds and textures (Bower & Parsons, 2003). And it coordinates voluntary movement. When a soccer player executes a perfect bicycle kick (right), give his cerebellum some credit. If you injured your cerebellum, you would have difficulty walking, keeping your balance, or shaking hands. Your movements would be jerky and exaggerated. Gone would be any dreams of being a dancer or guitarist. Under alcohol’s influence on the cerebellum, coordination suffers, as many a driver has learned after being pulled over and given a roadside test.


The brain’s organ of agility
Hanging at the back of the brain, the cerebellum coordinates our voluntary movements.


cerebellum  [sehr-uh-BELL-um]    the "little brain" at the rear of the brainstem; functions include processing sensory input and coordinating movement output and balance.

Note: These older brain functions all occur without any conscious effort. This illustrates another of our recurring themes: Our brain processes most information outside our awareness. We are aware of the results of our brain’s labor (say, our current visual experience) but not of how we construct the visual image. Likewise, whether we are asleep or awake, our brainstem manages its life-sustaining functions, freeing our newer brain regions to think, talk, dream, or savor a memory.

Retrieval Practice
  • In what brain region would damage be most likely to:

    1) disrupt your ability to skip rope?
    2) dirupt your ability to see and taste?
    3) perhaps leave you in a coma?
    4) cut off the very breath and heartbeat of life?

Limbic System

2-9: What are the limbic system’s structures and functions?

We’ve considered the brain’s oldest parts, but we’ve not yet reached its newest and highest regions, the cerebral hemispheres (the two halves of the brain). Between the oldest and newest areas lies the limbic system (limbus means "border"). This system contains the amygdala, the hypothalamus, and the hippocampus (FIGURE 2.18). The hippocampus processes conscious memories. Animals or humans who lose their hippocampus to surgery or injury also lose their ability to form new memories of facts and events. Chapter 8 explains how our two-track mind processes our memories. For now, let’s look at the limbic system’s links to emotions such as fear and anger, and to basic motives such as those for food and sex.


The limbic system
This neural system sits between the brain’s parts and its cerebral hemispheres. The limbic system’s hypothalamus controls the nearby pituitary gland.


limbic system      neural system (including the hippocampus, amygdala, and , hypothalamus) located below the cerebral hemispheres; associated with emotions and drives.

amygdala  [uh-MIG-duh-la]    two lima-bean-sized neural clusters in the limbic system; linked to emotion.


Research has linked the amygdala, two lima-bean-sized neural clusters, to aggression and fear. In 1939, psychologist Heinrich Klüver and neurosurgeon Paul Bucy surgically removed a rhesus monkey’s amygdala, turning the normally ill-tempered animal into the most mellow of creatures. In studies with other wild animals, including the lynx, wolverine, and wild rat, researchers noted the same effect.

What then might happen if we electrically stimulated the amygdala of a normally placid domestic animal, such as a cat? Do so in one spot and the cat prepares to attack, hissing with its back arched, its pupils dilated, its hair on end. Move the electrodes only slightly within the amygdala, cage the cat with a small mouse, and now it cowers in terror.

These and other experiments have confirmed the amygdala’s role in rage and fear, including the perception of these emotions and the processing of emotional memories (Anderson & Phelps, 2000; Poremba & Gabriel, 2001). But we must be careful. The brain is not neatly organized into structures that correspond to our behavior categories. When we feel or act in aggressive or fearful ways, there is neural activity in many levels of our brain. Even within the limbic system, stimulating structures other than the amygdala can evoke aggression or fear. If you charge a car’s dead battery, you can activate the engine Yet the battery is merely one link in an integrated system.

Retrieval Practice
  • Electrical stimulation of a cat’s amygdala provokes angry reactions, suggesting the amygdala’s role in aggression. Which ANS division is activated by such stimulation?


hypothalamus  [hi-po-THAL-uh-muss]    a neural structure lying below (hypo) the thalamus; it directs several maintenance activities (eating, drinking, body temperature), helps govern the endocrine system via the pituitary gland, and is linked to emotion and reward.

Just below (hypo) the thalamus is the hypothalamus (FIGURE 2.19), an important link in the command chain governing bodily maintenance. Some neural clusters in the hypothalamus influence hunger; others regulate thirst, body temperature and sexual behavior. Together, they help maintain a steady internal state.

As the hypothalamus monitors the state of your body, it tunes into your blood chemistry and any incoming orders from other brain parts. For example, picking up signals from your brain’s cerebral cortex that you are thinking about sex, your hypothalamus will secrete hormones.These hormones will in turn trigger the adjacent "master gland"your pituitary (see Figure 2.18), to influence your sex glands to release their hormones. These will intensify the thoughts of sex in your cerebral cortex. Once again, we see the interplay between the nervous and the endocrine systems: The brain influences the endocrine system, which in turn influences the brain.)

A remarkable discovery about the hypothalamus illustrates how progress in science often occurs - when curious, open-minded investigators make an unexpected observation. Two young McGill University neuropsychologists, James Olds and Peter Milner (1954), were trying to implant an electrode in a rat’s reticular formation when they made a magnificent mistake: They placed the electrode incorrectly (Olds, 1975). Curiously, as if seeking more stimulation, the rat kept returning to the location where it had been stimulated by the misplaced electrode. On discovering that they had actually placed the device in a region of the hypothalamus, Olds and Milner realized they had stumbled upon a brain center that provides pleasurable rewards (Olds, 1975).


The hypothalamus
This small but important structure, colored yellow/orange in this MRI scan photograph, helps keep the body's internal environment in a steady state.

Rat with an implanted electrode
With an electrode implanted in a reward center of its hypothalamus, the rat readily crosses an electrified grid, gladly accepting painful shocks, to press a pedal that sends electrical impulses to that center.


In a meticulous series of experiments, Olds (1958) went on to locate other "pleasure centers," as he called them (What the rats actually experience only they know, and they aren’t telling. Rather than attribute human feelings to rats, today’s scientists refer to reward centers, not "pleasure centers.")When allowed to press pedals to trigger their own stimulation in these areas, rats would sometimes do so at a feverish pace - up to 7000 times per hour - until they dropped from exhaustion. Moreover, to get this stimulation, they would even cross an electrified floor that even a starving rat would not cross to reach food (FIGURE 2.20).

Other limbic systme reward centers, such as the nucleus accumbens in front of the hypothalamus, were later discovered in many other species, including dolphins and monkeys. In fact, animal research has revealed both a general dopamine-related reward system and specific centers associated with the pleasures of eating, drinking, and sex. Animals, it seems, come equipped with built-in systems that reward activities essential to survival.

Contemporary researchers are experimenting with new ways of using limbic stimulation to control animals’s actions in future applications, such as search-and-rescue operations. By rewarding rats for turning left or right, one research team trained previously caged rats to navigate natural environments (Talwar et al., 2002; FIGURE 2.21). By pressing buttons on a laptop, the researchers were then able to direct the rat - which carried a reciever, power source, and video camera on a backpack - to turn on cue, climb trees, scurry along branches, and turn around and come back down.

Do humans have limbic centersfor pleasure? Indeed we do. To calm violent patients, one neurosurgeon implanted electrodes in such areas. Stimulated patients reported mild pleasure; unlike Olds’ rats, however, they were not driven to a frenzy (Deutsch, 1972; Hooper & Teresi, 1986).

Experiments have also revealed the effects of a dopamine-related reward system in people. One such research team had people rate the desirability of different vacation destinations. Then, after receiving either a dopamine-increasing drug or a sugar pill, they imagined themselves vacationing at half the locations. A day later, when presented with a pair of vacation spots they had initially rated equally, only the dopamine takers preferred the places they had imagined under dopamine’s influence (Sharot et al., 2009). The participants, it seems, associated the imagined experiences with dopamine-induced pleasant feelings.

Some researchers believe that addictive disorders, such as alcohol dependence, drug abuse, and binge eating, may stem from malfunctions in natural brain systems for pleasure and well-being. People genetically predisposed to this reward deficiency syndrome may crave whatever provides tha missing pleasure or relieves the negative feelings (Blum et al. 1996).


"If you were designing a robot vehicle to walk into the future and survive, .... you’d wire it up so that behavior ensured the survival of the self or the species - like sex and eating - would be naturally reinforcing."

Candace Pert (1986)


RatBot on a pleasure cruise
When stimulated by remote control, this rat could be guided to navigage across a field and even up a tree.


Figure 2.22
Review: Brain Structure and Function
Figure depicting previously discussed topics as well as the cerebral cortex, our next topic

Retrieval Practice
  • What are the 3 key structures, and what function do the serve?

Cerebral Cortex

2-10: What are the functions of the various cerebral cortex regions?

cerebral  [seh-REE-bruhl]  cortext  the intricate fabric of neural cells covering the cerebral hemispheres; the body’s ultimate control and information-processing center.

Older brain networks sustain basic life functions and enable memory, emotions, and basic drives. Newer neural networks with the cerebrum - the hemispheres that contribute 85 percent of the brain’s weight - form specialized work teams that enable our preceiving, thinking, and speaking. Like other structures above the brainstem (including the thalamus, hippocampus, and amygdala), the cerebral hemispheres come as a pair. Covering those hemispheres, like bark on a tree, is the cerebral cortex, a thin surface layer of interconnected neural cells. It is your brain’s thinking crown, your body’s ultimate control and information-processing center.

As we now move up the ladder of animal life, the cerebral cortex expaands, tight genetic controls relax, and the organism’s adaptability increases.Frogs and other small-cortex amphibians operate extensively on preprogrammed genetic instructions.The larger cortex of mammals offers increased capacities for learning and thinking, enabling them to be more adaptable. What makes us distinctively human mostly arises from the complex funcion of our cerebral cortex.

The people who first dissected and labeled the brain used the language of scholars - Latin and Greek. Their words are actually attempts at graphic description: For example, cortex means "bark" cerebellum is "little brain" and thalamus is "inner chamber."

Retrieval Practice
  • Which area of the human brain is most similar to that of less complex animals?

  • Which part of the human brain distinguishes us most from less complex animals?


glial cells (glia)      cells in the nervous system that support, nourish, and protect neurons; they may also play a role in learning and thinking.

frontal lobes      portion of the cerebral cortex lying just behind the forehead; involved in speaking and muscle movements and in making plans an judgments.

parietal  [puh-RYE-uh-tuhl]  lobes  portion of the cerebral cortex lying at the top of the head and toward the rear; receives sensory input for touch and body position.

occipital  [ahk-SIP-uh-tuhl]  lobes  portion of the cerebral cortex lying at the back of the head; includes areas the receive information from the visual fields.

temporal lobes      portion of the cerebral cortex lying roughly above the ears; includes the auditory areas, each receiving information primarily from the opposite ear.

If you opened a human skull, exposing the brain, you would see a wrinkled organ, shaped somewhat like he meat of an oversized walnut. Without these wrinkles, a flattened cerebral cortex would require triple the area - roughly that of a large pizza. The brain’s ballooning left and right hemispheres are filled mainly with axons connecting the cortex to the brain’s other regions. The cerebral cortex - that thin surface layer - contains soem 20 to 23 billion nerve cells and 300 trillion synaptic connections (de Courten-Myers, 2005). Being human takes a lot of nerve.

Supporting these billions of nerve cells are nine times as many spidery glial cells ("glue cells"). Neurons are like queen bees; on their own they cannot feed or sheathe themselves. Glial cells are worker bees.They provide nutrients and insulating myelin, guide neural connections, and mop up ions and neurotransmitters. Glia may also play a role in learning and thinking. By "chatting" with neurons they may participate in information transmission and memory (Fields, 2009; Miller, 2005).

In more complex animal brains, the proportion of glia to neurons increases. A postmortem analysis of Einstein’s brain did not find more or larger-than-usual neurons, but it did reveal a much greater concentration of glial cells than found in an average Albert’s head (Fields, 2004).

Each hemisphere’s cortex is subdivided into four lobes, separated by prominent fissures, or folds (FIGURE 2.23). Starting at the front of your brain and moving over the top, there are the frontal lobes (behind your forehead), the parietal lobes (at the top and to the rear), and the occipital lobes (at the back of your head). Reversing direction and moving forward, just above your ears, you find the temporal lobes. Each of the four lobes carries out many functions, and many functions require the interplay of several lobes.


The cortex and its basic subdivisions.


More than a century ago, surgeons found damaged cortical areas during autopsies of people who had been partially paralyzed or speechless. This rather crude evidence did not prove that specific parts of the cortex control complex functions like movement or speech. After all, if the entire cortex controlled speech and movement, damage to almost any area might produce the same effect. A TV with it power cord cut would go dead, but we would be fooling ourselves if we thought we had "localized" the picture in the cord.

Retrieval Practice

Try moving your right hand in a circular motion, as if polishing a table. Then start your right foot doing the same motion, synchronized with your hand. Now reverse the right foot’s motion, but noth the hand’s Finally, try moving the left foot opposite to the right hand.

  • Why is reversing the right foot’s motion so hard?

  • Why is it easier to move the left foot opposite to the right hand?

Motor Functions

Scientists had better luck in localizing simpler brain functions. For example, in 1870, German physicians Gustav Fritsch and Eduard Hitzig made an important discovery: Mild electrical stimulation to parts of an animals’s cortex made its body move. The effects were selective: Stimulation caused movement only when applied to an arch-shaped region at the back of the frontal lobe, running roughly ear-to-ear across the top of the brain. Moreover, stimulating parts of this region in the left or right hemisphere caused movements of specific body parts on the opposite side of the body. Fritsch and Hitzig had discovered what is now called the motor cortex.


motor cortex      an area at the rear of the frontal lobes that controls voluntary movements.

Lucky for brain surgeons and their patient, the brain has no sensory receptors. Knowing this, Otfrid Foerster and Wilder Penfield were able to map the motor cortex in hundreds of wide-awake patients by stimulating different cortical areas and observing the body’s responses. They discovered that body areas requiring precise control, such as the fingers and the mouth, occupy the greatest amount of cortical space (FIGURE 2.24).

In one of his many demonstrations of motor mechanics, Spanish neuroscientist JoséDelgado stimulated a spot on a patient’s left motor cortex, triggering the right hand to make a fist. Asked to keep the fingers open during the next stimulation, the patient, whose fingers closed despite his best efforts remarked, "I guess, Doctor, that your electricity is stronger than my will" (Delgado, 1969, p.114).

More recently, scientists were able to predict a monkey’s arm motion a tenth of a second before it moved - by repeatedly measuring motor cortex activity preceding specific arm movements (Gibbs, 1996). Such findings have opened the door to research on brain-controlled computers.


Left hemisphere tissue devoted to each body part in the motor cortex and the sensory cortex.
As you can see from this classic, though inexact representation, the amount of cortex devoted to a body part is not proportional to that part’s size. Rather, the brain devotes more tissue to sensitive areas and to areas requiring precise control. Thus, the fingers have a greater representation in the cortex than does the upper arm.

Brain - Computer Interface

By eavesdropping on the brain, could we enable someone - perhaps a paralyzed person - to move a robotic limb? Could a brain-computer interface command a cursor to write an e-mail or search the Internet? To find out, Brown University brain researchers implanted 100 tiny recording electrodes in the motor cortexes of three monkeys (Nicoleles & Chapin, 2002; Serruya et al., 2002). As the monkeys used a joystick to move a cursor to follow a moving red target (to gain rewards), the researchers matched the brain signals with arm movements. Then they programmed a computer to monitor the signals and operate the joystick. When a monkey merely thought about a move, the mind-reading computer moved the cursor wiht nearly the same proficiency as had the reward-seeking monkey. In a follow-up experiment (FIGURE 2.25), tow monkeys were trained to control a robot arm that could grasp and deliver food (Velliste et al. 2008).

Research has also recorded messages not from the arm-controlling motor neurons, but from a brain area involved in planning and intention (Leuthardt et. al., 2009; Musallam et al., 2004). In one study, a monkey seeking a juice reward awaited a cue telling it to reach toward a spot flashed on a screen in one of up to eight locations. A computer program captured the monkey’s thinking by recording activity in its planning-intention brain area. By matching this neural activity to the monkey’s subsequent pointing, the mind-reading researchers could program a cursor to move in response to the monkey’s thoughts. Monkey think, computer do.

If this technique works, why not use it to capture the words a person can think but cannot say (for example, after a stroke)? Cal Tech neuroscientist Richard Andersen (2004, 2005) has speculated that researchers could implant electrodes in speech areas, "ask a patient to think of different words and observe how the cells fire in different ways. So you build up your database, and then when the patient thinks of the word, you compare the signals with your database, and you can predict the words they’re thinking. Then you take this output and connect it to a speech synthesizer. This would be identical to what we’re doing for motor control."

Mind over matter
Guided by a tiny, 100-electrod brain implant, monkeys have learned to control a mechanical hand that can grab snacks and put them in their mouth. (Velliste et al., 2008). Although not yet permanently effective, such implants raise hopes that people with paralyzed limbs may someday be able to use their own brain signals to control computers and robotic limbs


Clinical trials of such cognitive nerual prosthetics are now underway with people who have suffered paralysis or amputation (Andersen et al., 2010). The first patient, a paralyzed 25-year-old man, was able to mentally control a TV, draw shapes on a computer screen, and play video games - all thanks to an aspirin-sized chip with 100 microelectrodes recording activity in his motor cortex (Hochberg et al., 2006). If everything psychological is also biological - if, for example, every thought is also a neural event - then microelectrodes perhaps could detect thoughts well enough to enable people to control events suggested by FIGURE 2.26


Brain-computer interaction
A patient with a severed spinal cord has electrodes planted in a parietal lobe region involved with planning to reach one’s arm. The resulting signal can enable the patient to move a robotic limb, stimulate muscles that activate a paralyzed limb, navigate a wheelchair, control a TV, and use the Internet. (Graphic adapted from Andersen et al., 2010.)

Sensory Functions

sensory cortex      area at the front of the parietal lobes that registers and processes body touch and movement sensations.

If the motor cortex sends messages out to the body, where does the cortex receive the incoming messages? Penfield also identified the cortical area that specializes in receiving information from the skin senses and from the movement of body parts.This area at the front of the parietal lobes, parallel to and just behind the motor cortex, we now call the sensory cortex (Figure 2.24). Stimulate a point onthe top of this band of tissue and a person may report being touched on the shoulder; stimulate some point on the other side and the person may feel something on the face.


The brain in action
This fMRI (functional MRI) scan shows the visual cortex in the occipital lobes activated (color representation of increased blood flow) as a research participant looks at a phtot. When the person stops looking, the region instantly calms down.

The more sensitive the body region, the larger the sensory cortex area devoted to it (Figure 2.24). Your supersenstive lips project to a larger brain area than do your toes, which is one reason we kiss with our lips rather than touch toes. Rats have a large area of the brain devoted to their whisker sensations, and owls to their hearing sensations.

The visual cortex and auditory cortex.
The visual cortex of the occipital lobes at the rear of your brain receives input from your eyes. The auditory cortex, in your temporal lobes - above your ears - receives information from your ears.


Scientists have identified additional areas where the cortex receives input from senses other than touch. At this moment, you are receiving visual information in the visual cortex in your occipital lobes, at the very back of your brain (FIGURES 2.27, 2.28). A bad enough bash there would make you blind. Stimulated there, you might see flashes of light or dashes of color. In a sense, we do have eyes in the back of our head!) From your occipital lobes, visual information goes to other areas that specialize in tasks such as identifying words, detecting emotions, and recognizing faces.

Any sound you now hear is processed by your auditory cortex in your temporal lobes (just above your ears; see Figure 2.28). Most of this auditory information travels a circuitous route from one ear to the auditory receiving area above your opposite ear. If stimulated there, you might hear a sound. MRI scans of people with schizophrenia reveal active auditory areas in the temporal lobes during auditory hallucinations (Lennox et al., 1999). Even the phantom ringing sound experienced by people with hearing loss is - if heard in one ear associated with activity in the temporal lobe on the brain’s opposite side (Muhlnickel, 1998).

Retrieval Practice
  • Our brain’s _______ cortex registers and processes bodily input.

  • The ______ cortex controls our voluntary movements.

Association Areas

association areas      areas of the cerebral cortex that are not involved in primary motor of sensory functions; rather, they are involved in higher mental functions such as learning, remembering, thinking, and speaking.

So far, we have pointed out small cortical areas that either receive sensory input or direct muscular output. Together, these occupy about ¼ of the human brain’s thin, wrinkled cover. What, then, goes on in the vast regions of the cortex? In these association areas (the peach-colored areas in FIGURE 2.29), neurons are busy with higher mental functions - many of the tasks that make us human.


Areas of the cortex in four mammals
More intelligent animals have increased "uncommitted" areas of the cortex. These vast areas of the brain are responsible for integrating and acting on information received and processed by sensory areas.

Electrically probing an association area won’t trigger any observable response. So, unlike the sensory and motor areas, association areas functions cannot be neatly mapped. Their silence has led to what Donald McBurney (1996, p. 44) has called "one of the hardiest weeds in the garden of psychology": the claim that we ordinarily use only 10 percent of our brains. (If true, wouldn’t this imply a 90 percent chance that a bullet to your brain would land in an unsed area?)Surgically lesioned animals and brain-damaged humans bear witness that association areas are not dormant. Rather, these areas interpret, integrate, and act on sensory information and link it with stored memories - a very important part of thinking.

Association areas are found in all four lobes. In the frontal lobes, they enable judgment, planning, and processing of new memories. People with damaged frontal lobes may have intact memories, high scores on intelligence tests, and great cake-baking skills. Yet they would not be able to plan ahead to begin baking a cake for a birthday party (Huey et al., 2006).

Frontal lobe damage also can alter personality and remove a person’s inhibitions. Consider the classic case of railroad worker Phineas Gage. One afternoon in 1848, Gage, then 25 years old, was packing gunpowder into a rock with a tamping iron. A spark ignited the gunpowder, shooting the rod up through list left cheek and out the top of his skull, leaving his frontal lobes massively damaged (FIGURE 2.30). To everyone’s amazement, he was immediately able to sit up and speak, and after the wound healed he returned to work. But the affable, soft-spoken man was not irritable, profane, and dishonest. This person, said his friends, was "no longer Gage." Although his mental abilities and memories were intact, his personality was not. (Although Gage lost his job, he did, over time, adapt to his injury and find work as a stagecoach driver [Macmillan & Lena, 2010].)

Phineas Gage reconsidered
(a) Gage’s skull was kept as a medical record. Using measurements and modern neuroimaging techniques, researchers have reconstucted the probable path of the rod through Gage’s brain (Damasio et al., 1994).

(b) This recently discovered photo shows Gage after his accident. The image has been reversed to show the features correctly. (Early photos, such as this one, are actually mirror images.)


More recent studies of people with damaged frontal lobes have revealed similar impairments. Not only may they become less inhibited (without the frontal lobe brakes on their impulses), but their moral judgments seem unrestrained by normal emotionsl Would you advocate pushing someone in front of a runaway boxcar to save five others? Most people do not, but those with damage to a brain area behind the eyes often do (Koenigs et al., 2007). With their frontal lobes ruptured, people’s moral compass seems to disconnect from their behavior.

Association areas also perform other mental functions. In the parietal lobes, parts of which were large and unusually shaped in Einstein’s normal-weight brain, they enable mathematical and spatial reasoning (Witelson et al., 1999). In patients undergoing brain surgery, stimulation of one parietal lobe produced a feeling of wanting to move an upper limb, the lips or the tongue (but without any actual movement. With increased stimulation, patients falsely believed they actually had moved. Curiously, when surgeons stimulated a different association area near the motor cortex in the frontal lobes, the patients did move but had no awareness of doing so (Desmurget et al., 2009). These head-scratching findings suggest that our perception of moving flows not from the movement itself, but rather from our intention and the results we expected.

Yet another association area, on the underside of the right temporal lobe, enables us to recognize faces. If a stroke or head injury destroyed this area of your brain, you would still be able to describe facial features and to recognize someone’s gender and approximate age, yet be strangely unable to identify the person as, say, Lady Gaga, or even your grandmother.

Nevertheless, we should be wary of using pictures of brain "hot spots" to create a new phrenology that locates complex functions in precise brain areas (Uttal, 2001). Complex mental functions don’t reside in any one place. There is no one spot in a rat’s small association cortex that, when damaged; will obliterate its ability to learn or remember a maze. Memory, language, and attention result from the synchronized activity among distinct brain areas (Knight, 2007). Ditto for religious experience. Reports of more than 40 distinct brain regions becoming active in different religious states, such as praying and meditating, indicate there is no simple "God Spot" (FingelKurts & FingelKurts, 2009). The big lesson: Our mental experiences arise from coordinated brain activity.

Retrieval Practice
  • Why are association areas important?


2-11: To what extent can a damaged brain reorganize itself, and what is neurogenesis?

plasticity      the brain’s ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience.

Our brains are sculpted not only by our genes but also by our experiences. MRI scans show that well-practiced pianists hava a larger-than-usual auditory cortex area that encodes piano sounds Bavelier et al., 2000; Pantev et al., 1998). In Chapter 4, we’ll focus more on how experience molds the brain.For now, let’s turn to another aspect of the brain’s plasticity: its ability to modify itself after damage.

Some of the effects of brain damage described earlier can be traced to two hard facts:

1) Severed neurons, unlike cut skin, usually do not regenerate.
  (If your spinal cord were severed, you would probably be permanently paralyzed)

2) Some brain functions seem preassigned to specific areas.

One newborn who suffered damage to temporal lobe facial recognition areas later remained unable to recognize faces (Farah et al., 2000). But there is good news: Some neural tissue can reorganize in response to damage. Under the surface of our awareness, the brain is constantly changing, building new pathways as it adjusts to little mishaps and new experiences.


Brain plasticity
This 6-year-old had surgery to end her life-threatening seizures. Although most of an entire hemisphere was removed (see MRI below) her remaining hemisphere compensated by putting other areas to work. One Johns Hopkins medical team reflected on the child hemispherectomies thay had performed. Although use of the opposite hand is compromised, they reported being "awed" by how well these children had retained their memory, personality, and humor (Vining et al., 1997). The younger the child, the greater the chance that the remaining hemisphere can take over the functions of the one that was surgically removed (Choi, 2008).

Plasiticity may also occur after serious damage, especially in young children (Kolb, 1989; see also FIGURE 2.31). Constraint-induced therapy aims to rewire brains and improve the dexterity of a brain-damaged child or even an adult stroke victim (Taub, 2004). By restraining a fully functioning limb, therapists force patients to use the "bad" hand or leg, gradually reprogramming the brain. One stroke victim, a surgeon in his fifties, was put to work cleaning tables, with his good arm and hand restrained. Slowly, the bad arm recovered its skills. As damaged-brain functions migrated to other brain regions, he gradually learned to write again and even to play tennis (Doidge, 2007).


The brain’s plasticity is good news for the blind or deaf. Blindness or deafness makes unused brain areas available for other uses (Amedi et al., 2005). If a blind person uses one finger to read Braille, the brain area dedicated to that finger expands as the sense of touch invades the visual cortex that normally helps people see (Barinaga, 1992a; Sadato et al., 1996). If magnetic stimulation temporarily "knocks out" the visual cortex, a lifelong-blind person will make more errors on a language task (Amedi et al., 2004).

Plasticity also helps explain why some studies find that deaf people have enhanced peripheral vision (Bosworth & Dobkins, 1999). In those people whose native language is sign, the temporal lobe area normally dedicated to hearing waits in vain for stimulation. Finally, it looks for other signals to process, such as those from the visual system.

Similar reassignment may occur when disease or damage frees up other brain areas normally dedicated to specific functions. If a slow-growing left hemisphere tumor disrupts language (which resides mostly in the left hemisphere), the right hemisphere may compensate (Thiel et al., 2006). If a finger is amputated, the sensory cortex that received its input will begin to receive input from the adjacent fingers, which then become more sensitive (Fox, 1984). So what do you suppose was the sexual intercourse experience of one patient whose lower leg had been amputated? (Note, too, in Figure 2.24, that the toes region is adjacent to the genitals.) "I actually experience my orgasm in my foot. And there it’s much bigger that it used to be because it’s no longer confined to just my genitals"(Ramachandran & Blakeslee, 1998, p.36).

Although the brain often attempts self-repair by reorganizing existing tissue, it sometimes attempts to mend itself by producing new brain cells. This process, known as neurogenesis, has been found in adult mice, birds, monkeys, and humans (Jessberger et al., 2008). These baby neurons originate deep in the brain and may then migrate elsewhere and form connections with neighboring neurons (Aimone et al., 2010; Gould, 2007).

neurogenesis      the formation of new neurons

Master stem cells that can develop into any type of brain cell have also been discovered in the human embryo. If mass-produced in a lab and injected into a damaged brain, might neural stem cells turn themselves into replacements for lost brain cells? Might we someday be able to rebuild damaged brains, much as we reseed damaged lawns? Might new drugs spur the production of new nerve cells? Stay tuned. Today’s biotech companies are hard at work on such possibilities. In the meantime, we can all benefit from other natural promoters of neurogenesis, such as exercise, sleep, and nonstressful but stimulating environments Iso et al., 2007; Perira et al., 2007; Stranahan et al., 2006).

The Divided Brain

2-12: What do split brains reveal about the functions of our two brain hemispheres?

We have seen that our brain’s look-alike left and right hemispheres serve differing functions. This lateralization is apparent after brain damage. Research collected over more than a century has shown that accidents, strokes, and tumors in the left hemisphere can impair reading, writing, speaking, arithmetic reasoning, and understanding. Similar lesions in the right hemisphere seldom have such dramatic effects.

Does this mean that the right hemisphere is just along for the ride - a silent, "subordinate" or "minor" hemisphere? Many believed this was the case until 1960, when researchers found that the "minor" right hemisphere was not so limited after all. The story of this discovery is a fascinating chapter in psychology’s history

Splitting into Hemispheres

corpus callosum  [KOR-pus-kah-LOW-sum]    the large band of neural fibers connecting the two brain hemispheres and carrying messages between them.

split brain      a condition resulting from surgery that isolates the brain’s two hemispheres by cutting the fibers (mainly those of the corpus callosum) connecting them.

In 1961, two Los Angeles neurosurgeons, Philip Vogel and Joseph Bogen, speculated that major epileptic seizures were caused by an amplification of normal brain activity bouncing back and forth between the two cerebral hemispheres. If so, they wondered, could they put an end to this biological tennis game by severing the corpus callosum (FIGURE 2.32)? This wide band of axon fibers connects the two hemispheres and carries messages between them. Vogel and Bogen knew that psychologists Roger Sperry, Ronald Myers, and Michael Gazzaniga had divided the brains of cats and monkeys in this manner, with no serious ill effects.

So the surgeons operated. The result? The seizures all but disappeared. The patients with these split brains were surprisingly normal, their personality and intellect hardly affected. Waking from surgery, one even joked that he had a "splitting headache" (Gazzaniga, 1967). By sharing their experiences, these patients have greatly expanded our understanding of interactions between the intact brain’s two hemispheres.

The corpus callosum
This large band of neural fibers connects the two brain hemispheres. To photograph the half brain, shown at left, a surgeon separated the hemispheres by cutting through the corpus callosum and lower brain regions. In the view on the right, brain tissue has been cut back to expose the corpus callosum and bundles of fibers coming out from it.


The information highway from eye to brain.


To appreciate these findings, we need to focus for a minute on the peculiar nature of our visual wiring. As FIGURE 2.33 illustrates, information from the left half of your field of vision goes to your right hemisphere, and information from the left half of your field of vision goes to your right hemisphere, and information from the right half of your field of vision goes to your left hemisphere, which usually controls speech. (Note, however, that each eye receives sensory information from both the right and left visual fields.) Data received by either hemisphere are quickly transmitted to the other across the corpus callosum. In a person with a severed corpus callosum, this information sharing does not take place.

Knowing these facts, Sperry and Gazzaniga could send information to a patient’s left or right hemisphere. As the person stared at a spot, they flashed a stimulus to its right or left.They could do this with you, too, but in your intact brain, the hemisphere receiving the information would instantly pass the news to the other side.Because the split-brain surgery had cut the communication lines between the hemispheres, the researchers could, with these patients, quiz each hemisphere separately.

In an early experiment, Gazzaniga (1967) asked these people to stare at a dot as he flashed HE · ART on a a screen (FIGURE 2.34). Thus, HE appeared in their left visual field (which transmits to the right hemisphere) and ART in the right field (which transmits to the left hemisphere). When he then asked them to say what they had seen, the patients reported that they had seen ART. But when asked to point to the word they had seen, they were startled when their left hand (controlled by the right hemisphere) pointed to HE. Given an opportunity to express itself, each hemisphere reported what it had seen. The right hemisphere (controlling the left hand) intuitively knew what it could not verbally report.

When a picture of a spoon was flashed to their right hemisphere, the patients could not say what they had viewed. But, when asked to identify what they had viewed by feeling an assortment of hidden objects with their left hand, they readily selected the spoon. If the experimenter said, "Correct!" the patient might reply, "What? Correct? How could I possibly pick out the correct object when I don’t know what I saw? "If is, of course, the left hemisphere doing the talking here, bewildered by what the nonverbal right hemisphere knows.


Testing the divided brain
When an experimenter flashes the word HEART across the visual field, a woman with a split brain reports seeing the portion of the word transmitted to her left hemisphere. However, if asked to indicate with her left hand what she saw, she points to the portion of the word transmitted to her right hemisphere. (From Gazzaniga, 1983.)

"Do not let your left hand know what your right hand is doing"

Matthew 6:3

A few people who have had split-brain surgery have been for a time bothered by the unruly independence of their left hand, which might unbutton a shirt while the right hand buttoned it, or put a grocery store items back on the shelf after the right hand put them in the cart. It was as if each hemisphere was thinking "I’ve half a mind to wear my green (blue) shirt today." Indeed said Sperry (1964), split-brain surgery leaves people "with two separate minds." With a split brain, both hemispheres can comprehend and follow an instruction to copy - simultaneously - different figures with the left and right hands (Franz et al., 2000). Reading these reports, I fantasize a patient enjoying a solitary game of "rock, paper, scissors" - left versus right hand.

When the "two minds" are at odds, the left hemisphere does mental gymnastics to rationalize reactions it does not understand. If a patient follows and order send to the right hemisphere ("Walk"), a strange thing happens. Unaware of the order, the left hemisphere doesn’t know why the patient begins walking. Yet, when asked why, the patient doesn’t say "I don’t know." Instead the interpretive left hemisphere improvises - "I’m going into the house to get a Coke." Gazzinga (1988), who considers these patients "the most fascinating people on earth," concluded that the conscious left hemisphere is an "interpreter" or press agent that instantly constructs theories to explain our behavior.

Figure 2.35
Try this!
Joe, who has had split-brain surgery, can simultaneously draw two different shapes.

Retrieval Practice

If we flash a red light to the right hemisphere of a person with a split brain, and flash a green light to the left hemisphere...

  • Will each observe its own color?

  • Will the person be aware that the colors differ?

  • What will the person verbally report seeing?

Right Left Differences of the Intact Brain

So, what about the 99.99+% of us with undivided brains? Does each of our hemispheres also perform distinct functions? Several different types of studies indicate they do. When a person performs a perceptual task, for example, brain waves, bloodflow, and glucose consumption reveal increased activity in the right hemisphere. When the person speaks or calculates, activity increases in the left hemisphere.

A dramatic demonstration of hemispheric specialization happens before some types of brain surgery. To locate the patient’s language centers, the surgeon injects a sedative into the neck artery feeding blood to the left hemisphere, which usually controls speech. Before the injection, the patient is lying down, arms in the air, chatting with the doctor. Can you predict what probably happens when the drug puts the left hemisphere to sleep? Within seconds, the person’s right arm falls limp. If the left hemisphere is controlling language, the patient will be speechless until the drug wears off. If the drug is injected into the artery to the right hemisphere, the left arm will fall limp, but the person will still be able to speak.

To the brain, language is language, whether spoken or signed. Just as hearing people usually use the left hemisphere to process speech, deaf people use the left hemisphere to process sign language (Corina et al., 1992; Hickok et al., 2001). Thus, a left-hemisphere stroke disrupts a deaf person’s signing, much as it would disrupt a hearing person’s speaking.The same brain area is involved in both (Corina, 1998). (For more on how the brain enables language, see Chapter 9.)


Pop psychology’s idea of hemispheric specialization
Alas, reality is more complex

Although the left hemisphere is adept in making quick, literal interpretations of language, the right hemisphere:

  • excels in making inferences (Beeman & Chiarello, 1998; Bowden & Beeman, 1998; Mason & Just, 2004). Primed with the flashed word foot, the left hemisphere will be especially quick to recognize the closely associated word heel. But if primed with foot, cry, and glass, the right hemisphere will more quickly recognize another word distantly related to all three (cut). And if given an insightlike problem - "What word goes with boot, summer, and ground?" the right hemisphere more quickly than the left recognizes the solution: camp. As one patient explained after a right hemisphere stroke, "I understand the words, but I’m missing the subtleties."

  • helps us modulate our speech to make meaning clear - as when we ask "What’s that in the road ahead?" instead of "What’s that in the road, a head?" (Heller, 1990).

  • helps orchestrate our sense of self. People who suffer partial paralysis will sometimes obstinately deny their impairment - strangely claiming they can move a paralyzed limb - if the damage is in the right hemisphere (Berti et al., 2005).

Simply looking at the two hemispheres, so alike to the naked eye, who would suppose they contribute uniquely to the harmony of the whole? Yet a variety of observations - of people with split brains, of people with normal brains, and even of other species’ brains - converge beautifully, leaving little doubt that we have unified brains with specialized parts (Hopkins & Cantalupo 2008; MacNeilage et al., 2009; and see Close-Up: Handedness).

In this chapter we have glimpsed an overriding principle: Everything psychological is simultaneously biological. We have focused on how our thoughts, feelings, and actions arise from our specialized yet integrated brain. In chapters to come, we will further explore the significance of the biological revolution in psychology.

From nineteenth-century phrenology to today’s neuroscience, we have come a long way. Yet what is unknown still dwarfs what is known. We can describe the brain. We can learn the functions of its parts. We can study how the parts communicate. But how do we get mind out of meat? How does the electrochemical whir in a hunk of tissue the size of a head of lettuce give rise to elation, a creative idea, or that memory of Grandmother?

Much as gas and air can give rise to something different - fire - so also, believed Roger Sperry, does the complex human mind give rise to something different: consciousness. The mind, he argued, emerges from the brain’s dance of ions, yet is not reducible to it. Cells cannot be fully explained by the actions of atoms, nor minds by the activity of cells. Psychology is rooted in biology, which is rooted in chemistry, which is rooted in physics. Yet psychology is more than applied physics. As Jerome Kagan (1998) reminded us, the meaning of the Gettysburg Address is not reducible to neural activity. Sexual love is more than blood flooding to the genitals. Morality and responsibility become possible when we understand the mind as a "holistic system," said Sperry (1992)(FIGURE 2.37).

Mind and brain as holistic system
In Roger Sperry’s view, the brain creates and controls the emergent mind, which in turn influences the brain. (Think vividly about biting into a lemon and you may salivate.)


The mind seeking to understand the brain - that is indeed among the ultimate scientific challenges. And so it will always be. To paraphrase cosmologist John Barrow, a brain simple enough to be understood is too simple to produce a mind able to understand it.

Handed - Ness

Nearly 90 percent of us are primarily right-handed (Leask & Beaton, 2007; Medland et al., 2004; Peters et al., 2006). Some 10 percent of us (somewhat more among males, somewhat less among females) are left-handed. (A few people write with their right hand and throw a ball with their left, or vice versa.) Almost all right-handers (96 percent) process speech primarily in the left hemisphere, which tends to be the slightly larger hemisphere (Hopkins, 2006). Left-handers are more diverse. Seven in ten process speech in the left hemisphere, as right-handers do. The rest either process language in the right hemisphere or use both hemispheres.

Is Handedness Inherited?

Judging from prehistoric human cave drawings, tools, and hand and arm bones, this veer to the right occurred long ago (Corballis, 1989; MacNeilage et al., 2009). Right-handedness prevails in all human cultures, and even in monkeys and apes. Moreover, it appears prior to culture’s impact: More than 9 in 10 fetuses suck the right hand’s thumb (Hepper et al., 1990, 2004). Twin studies indicate only a small genetic influence on individual handedness (Vuoksimaa et al., 2009). But the universal prevalence of right-handers in humans and other primates suggests that either genes or some other prenatal factors influence handedness.

The rarest of baseball players: an ambidextrous pitcher
Using a glove with two thumbs, Creighton University pitcher Pat Veditte, shown here in a 2008 game, pitched to right-handers with his right hand, then switched to face left-handed batters with his left hand. After one switch-hitter switched sides of the plate, Veditte switched pitching arms, which triggered the batter to switch again, and so on. The umpires ultimately ended the comedy by applying a little-known rule: A pitcher must declare which arm he will use before throwing his first pitch to a batter. (Schwarz, 2007).


"Most people also kick with their right foot, look through a microscope with their right eye, and (had you noticed?) kiss the right way - with their head tilted right"

Güntürkün, 2003).

So is it all right to be Left-Handed?

Judging by our everyday conversation, left-handedness is not all right. To be "coming out of left field" is hardly better than to be "guauche" (derived from the French word for "left" ). On the other hand, right-handedness is "right on" which any "righteous", "right-hand man" "in his right mind" usually is.

Left-handers are more numerous than usual among those with reading disabilities, allergies, and migraine headaches (Geschwind & Behan, 1984). But in Iran, where students report which hand they write with when taking the university entrance exam, lefties have outperformed righties in all subjects (Noroozian et al., 2003). Left-handedness is also more common among musicians, mathematicians, professional baseball and cricket players, architects, and artists, including such luminaries as Michelangelo, Leonardo da Vinci, and Picasso. Although left-handers must tolerate elbos jostling at the dinner table, right-handed desks, and awkward scissors, the pros and cons of being a lefty seem roughly equal.

Retrieval Practice
  • Almost all right-handers (96 percent) process in the ______ hemisphere

  • Most left-handers (70 percent) process speech in the ______ hemisphere.