2 - brain, body, and behavior

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Chapter Outline How the Brain Govems Behavior The brain's communication system How neurons send their messages The links of the nervous system The cerebral cortex and how it makes us human How Neuroscientists Study the Brain and Mind Structural brain imaging Functional brain imaging Electroencephalography The Brain's Functions, I: Experiencing the World Sensing and interpreting the environment Processing and transmitting sensory information Generating body movements Managing coordination and balance The Brain's Functions, II: Overseeing Emotions and Survival The wellsprings of passions and feelings Staying alive and physiologically in tune The autonomic nervous system: The brain's busy deputy The brain's hemispheres and the regulation of emotion The Brain's Functions, III: Managing Thought and Memory Thinking and planning How memories are stored and retrieved The growing brain and the developing intellect Left brain, right brain The Brain-Behavior Link Transforming electricity and chemistry into meanings and feelings The interplay of biological, psychological, and environmental forces Summary Test Yourself Answers Study Guide Psychology in the Lab and in Life: How the Brain Restores Its Functions Psychology and the Media: Neuroscience in the Future Life Span Perspedive: As the Brain Matures

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Chapter

Outlinesystem

The Brain-Behavior LinkTransforming electricity and chemistry into meanings and feelings The interplay of biological, psychological, and environmental forces

How the Brain Govems BehaviorThe brain's communication How neurons send their messages The links of the nervous system The cerebral cortex and how it makes us human

How Neuroscientists Study the Brain and MindStructural brain imaging Functional brain imaging Electroencephalography

Summary Test Yourself Answers Study GuidePsychology in the Lab and in Life: How the Brain Restores Its Functions Psychology and the Media: Neuroscience in the Future Life Span Perspedive: As the Brain Matures

The Brain's Functions, I: Experiencing the WorldSensing and interpreting the environment Processing and transmitting information Generating body movements Managing coordination and balance sensory

The Brain's Functions, II: Overseeing Emotions and SurvivalThe wellsprings of passions and feelings Staying alive and physiologically in tune The autonomic nervous system: The brain's busy deputy The brain's hemispheres and the regulation of emotion

The Brain's Functions, III: Managing Thought and MemoryThinking and planning How memories are stored and retrieved The growing brain and the developing intellect Left brain, right brain

1. Interview two people you know well, and attempt to construct a case history for each person. Begin by asking what they think are their major personality characteristics-intelligent, outgoing, athletic, and so on. For each characteristic, such as athletic, ask about their first recollections. Why do they think they developed that characteristic, and what factors or events in their past were influential in contributing to it? Concentrate on asking why they did the things they did, what they felt might have happened to them if they had or had not done certain things, and how they felt about themselves and other people. Then try to piece together a cohesive explanation for how the particular characteristic developed in each person. Provide different interpretations of this development from the strict-behaviorist, Gestalt, cognitive, and humanistic perspectives, as well as from the standpoint of the nature-nurture, change-continuity, and individual-context issues. 2. The experimental method is the primary approach psychologists use to determine the causes of behavior. In a simple experiment, participants are randomly assigned to two groups that are treated differently in only one respect-the independent variable. If their behavior then differs by groups, the difference can be attributed to the independent variable. But research is not always this straightforward. Sometimes the difference in behavior can be explained by something other than the independent variable. Below are descriptions of a few hypothetical experiments and conclusions. Write a short discussion of each, pointing out the inadequacies of the experiment for drawing the stated conclusions. Try to suggest factors other than the one mentioned that might have produced the results. Also note any ethical problems that might have arisen. a. Back in the days of "traditional" childbirth, U.S. mothers were allowed only minimal con-

tact with their newborns during the first several hours after birth. To assess whether mothers might be missing something important, researchers arranged for one group to have the traditional minimal contact and another to have several extra hours of contact with their babies. A year later, the "extended contact" mothers were noticeably more emotionally attached to their infants than were mothers in the "traditional" group. The researchers concluded that the first several hours after birth are a highly important period for fostering mother-to-child emotional attachment. b. To test the effects of marijuana on memory, some participants were asked to smoke one marijuana cigarette before memorizing a list of words; other participants instead were asked to smoke one tobacco cigarette. The marijuana group did poorly on the task compared to the tobacco group, and the researcher concluded that marijuana impairs memory. It has been found that children who play violent video and computer games are more aggressive in their play with other children than are children who do not play these games. Therefore, playing violent games makes children more aggressive toward others. An editor of a popular U.S. men's magazine published the results of a readers' survey indicating that by far the majority of men "cheat" on their spouses or partners on more than one occasion, and the longer the two are together, the more likely cheating becomes. The editor concluded that men in general are biologically incapable of being faithful and that the few exceptions in the survey "prove the rule."

c.

d.

"I~

For quizzing, activities, exercises, and web links, check out the book-specific website at www.cengage.com/psychology.

It perches on top of your spine, within your skull-3 pounds of pink, soft, strangely wrinkled tissue the size of a grapefruit. In weight, it makes up less than 2% of your body, yet it works so hard that it consumes about 20% of the oxygen that the body uses when at rest. Nature has devised ways to protect it. In addition to being encased in the thick bone of your skull, it is surrounded by a fluid that helps cushion it. And when your body is deprived of food, it is the first to get its share of whatever nutrients are coursing through the blood. "It" is the human brain, which has been described as "the most marvelous structure in the universe" (Miller, 1990). (See Figure 2.1.) All the human capabilities discussed in this textbook-gathering information, learning and remembering, acting intelligently, moving about, developing skills, feeling emotions, coping with stress, relating to others-as well as surviving from moment to moment are managed within the brain. Think of all the things you did in the last 24 hours. Whatever you did-sleep, dream, wake up, dress, eat, study, get angry, make love-your brain was responsible. We function through a network of brain and body systems that is surely one of the great wonders of nature. Knowledge of how these systems work and exactly what they accomplish is essential to an understanding of the entire field of psychology.

FIGURE 2.1 A side view of the human brain. The brainperches on top of vour spine, beneath vour skull-3 pounds of pinkish, soft, strangelv wrinkled tissue the size of a 9 rapefru it.

HOW THE BRAIN GOVERNS BEHAVIORTo appreciate the remarkable powers of the brain, it helps to understand how lower organisms manage to function. A FOCUS QUESTIONS How do neurons work and what do they do? one-celled animal such as a paramecium doesn't need a ner What constitutes the central nervous system? vous system. Its entire single-celled "body" is sensitive to Why do psychologists and other scientists place heat and light and capable of initiating the movements necso much emphasis on understanding the functions essary for life. Larger and more complicated animals, howof the brain's outer surface? ever, must have some kind of nervous system to coordinate their internal functions and movements. This system takes the form of specialized neural fibers that extend throughout the body and are capable of transmitting information back and forth.

Neuron The neural cell; the basic unit of the nervous system. Hormone A biochemical that typically is released into the bloodstream to perform its function at locations distant from the brain, but that can also affect brain functioning itself.

The key to the human brain's mastery is a web of connected pathways running within the brain and to other parts of the body. The brain carries out its many functions through a constant exchange of information, speeding along these trillions of pathways. Indeed, without them, the brain would be helpless to direct and manage our behavior or even to keep us alive.

The Brain's Communication

System

GliaCells that perform a wide array of functions such as regulating the biochemical environment of the brain, helping sustain neurons, modulating neural transmission, and aiding in the repair of neurons in case of injury. They are also important in early brain development and maturation. Dendrites The primary "receiving" parts of a neuron. Cell body The part of a neuron that converts oxygen, sugars, and other nutrients into energy. Nucleus The core of the ce II body of a neuron or other cell, containing the genes. Receptor sites Spots on the cell body of a neuron that, like the dendrites, can be stimulated by other neurons.

AxonThe fibrous body of a neuron that carries the neural impulse to the terminal branches. Terminal branches The parts of a neuron that send messages to other neurons or to muscles or glands. Myelin sheath A whitish coating of fatty protective tissue that "insulates" the axons of neurons.

The brain contains a staggeringly large number of neurons, or neural cells-eertainly many billions, and perhaps as many as a few trillion (Nicholls, Martin, Wallace, & Fuchs, 2001). Each neuron can receive messages from thousands of other neurons, process these messages in various ways, and then pass its own messages along to thousands more. The total number of possible connections is so great that it defies the imagination. One estimate is 50 trillion (Rosenzweig & Lieman, 1982). Thus, the brain is an intricate tapestry of connections, interconnections, and structures. Little wonder that the brain has been described as "the most complex structure in the known universe" (Fischbach, 1992). Although the diverse neurons of the brain primarily transmit messages, some operate like miniature glands, producing complex biochemicals called hormones (from the Greek word meaning "activators" or "exciters") (Nicholls et al., 2001). The various hormones, which are discussed at relevant points in the chapter, are typically released into the bloodstream to perform their functions at locations distant from the brain, but some also affect the functioning of the brain itself. The rest of the brain is made up of cells called glia, from the Greek word for "glue," so named because of the 19th-century idea that they primarily bind neurons together and otherwise provide physical support. Although there is little evidence that this is one of their many roles, the idea has persisted (Purves et aI., 1997). Glia-which are every bit as diverse in form as neurons and even more numerous-are known to perform a wide array of functions such as regulating the biochemical environment of the brain, helping sustain neurons, modulating neural transmission, and aiding in the repair of neurons in case of injury; they are likewise important in early brain development and maturation (Laming et al., 2000). It is hard to imagine the amount of activity taking place in your nervous system. Right now, for example, messages rich in information are being "flashed" back and forth to every part of your body. The messages take the form of neural impulses, which resemble tiny electrical charges, each strong enough to register only on the most sensitive recording devices. The neurons start sending their messages long before birth and continue to hum with activity throughout the life span. These tiny impulses somehow account for all the accomplishments of the brain, and thus understanding neural transmission in all its complexity is the key to understanding relationships between the brain and behavior-both physical and cognitive. Neurons come in a great many varieties and often bear little resemblance to one another, except that they generally share the characteristics illustrated in Figure 2.2. First are the dendrites, the primary receivers of stimulation from preceding neurons. Next is the cell body, which has a nucleus, or core, containing the genes that caused the cell to grow into a neuron in the first place. The cell body performs the process of metabolism, converting oxygen, sugars, and other nutrients supplied by the bloodstream into energy to both sustain the neuron and allow it to function. The surface of the cell body is dotted with numerous receptor sites, which-like the tips of the dendrites-are capable of responding to stimulation. When dendrites and receptor sites are sufficiently stimulated, they cause the neuron to "fire" and send an impulse down the axon to the terminal branches, which are the neuron's "senders"; they stimulate (or inhibit) the neurons next in line.

A myelin sheath coats the axon of many, but by no means all, neurons. Another role of the glia is to produce this whitish coating of fatty protective tissue, which functions somewhat like insulation on electrical wiring, increasing the efficiency of the neuron's operation. Transmission is further improved by the nodes, constrictions of the myelin sheath that act as booster stations, helping to "nudge" the neural impulse along the axon to the terminal branches. Some neurons terminate in glands or muscles, where they stimulate or inhibit action. However, most of the neurons in the brain connect exclusively with other neurons, forming intricate circuits that combine to form the systems and networks that perform the specific functions of the brain.

/----

Dendrites

How Neurons Send Their MessagesA neural impulse-the tiny charge that passes down the length of the axon at perhaps 100 mph (160 kph)can best be compared to the glowing band of fire that travels along a lit fuse. A neuron ordinarily operates on what is called the all-or-none principle. That is, either it fires or it doesn't. A neural impulse can only travel the length of the neuron that produced it-from dendrites or receptor sites to the terminal branches of the axon. There it stops. But when it reaches the ends of the terminal branches, it sets off events that influence the receiving neurons and deliver the message. FIGURE 2.2 A more or less typical neuron. Neurons come The key to transmission of the message is the in many varieties. Essential features are dendrites at one end, synapse, the connecting point where a terminal terminal branches at the other, and a cell body and fibrous axon branch of one neuron is separated by only a microin between. scopic distance-a millionth of an inch-from a dendrite or receptor site of another neuron. At the synapse, where the two neurons almost touch, the first influences the second through the reNodes lease of chemical neurotransmitters. When the neuron fires, a burst of these bioConstrictions of the myelin chemically active substances is released at the synapse. The chemicals flow across sheath of an axon that act as the tiny gap between the two neurons (the synaptic cleft) and act on the second neubooster stations for neural ron, either exciting it to fire (if a sufficient amount is present) or inhibiting its firing. impulses. Figure 2.3 is a photograph of parts of a neuron that play an especially important role in the transmission of messages-the little swellings called synaptic knobs All-or-none principle at the very tips of the terminal branches of the neuron. It is these knobs that actuThe general rule that a neuron ally form synapses with other neurons at their dendrites or cell body receptor sites. either fires or doesn't. An enlarged drawing of a synapse is shown in Figure 2.4. In the first neuron, Synapse the neurotransmitter is produced in the cell body and delivered down the length of The connecting point where a the fiber to the synaptic vesicles, where it is stored until called upon. When the neuterminal branch of one neuron ron fires, the neural impulse reaching the synaptic knob causes the vesicles to reis only a microscopic distance lease their transmitter chemicals. These neurotransmitters flow across the synaptic from a dendrite or receptor cleft and act on the receptors of the second neuron. Some of the neurotransmitters site of another neuron. stimulate the second neuron to fire. Others do the opposite, instructing the second neuron to refrain from firing-that is, inhibiting activity in the second neuron. Neu rotransmitters Whether the neuron fires or not depends on the overall pattern of messages it Biochemicals released at receives. Ordinarily, it will not fire in response to a single message arriving at one of neuron synapses that aid or its many dendrites or receptor sites. Instead, the firing process requires multiple inhibit neural transmission.

FIGURE 2.3 Synaptic knobs. This photograph, taken at about 2,000 times life size, was the first ever made of the synaptic knobs. It shows some of the structures in a snail.Lewis, Zeevi, & Everhart, 1969.

FIGURE 2.4 Where neuron meets neuron: the synapse. The terminal branch of the first neuron ends in a synaptic knob, separated from the second neuron bV onlv a tiny gap called the synaptic cleft.stimuli-a whole group of messages arriving at once or in quick succession from the other neurons with which it has synaptic contact. The overall stimulation must outweigh the overall inhibition if the neuron is to fire. Although the electrochemical messages travel in complex ways, the process is highly organized. Neural cells are arranged in ways that permit those engaged in similar tasks to work together. The chemical receptors on the neurons are quite specific; they recognize only certain kinds of neurotransmitters. Neurons that send or receive the same neurotransmitters form special circuits, or pathways. Small wonder that the human nervous system is capable of so much.

-----Synaptic vesicles

Dendrite or cell-body receptor site of second neuron

The Links of the Nervous System

Spinal cord The thick cable of neurons that mostlv connects PNS neurons to the brain. Central nervous system (CNS) The brain and the spinal cord. Peripheral nervous system (PNS) The network of neurons outside of the eNS.

The neurons of the brain can affect our behavior only because there are links between them and other parts of the body. These links constitute the rest of the nervous system, which is composed of neurons of various kinds. The neuron fibers of the nervous system-the axons identified in Figure 2.2-extend throughout the body. Together, the brain and the spinal cord are known as the central nervous system (eNS). The spinal cord is like a master cable that connects the brain with much of the rest of the body. The neurons that lie outside these structures constitute the peripheral nervous system (PNS), a network that extends throughout the body, all the way to the fingertips and toes. Neurons differ greatly, as noted earlier, but they can be grouped into three classes based on their function, which is fixed and unchanging: (1) Afferent neurons originate in the sense organs and body, and they carry messages from our eyes, ears, and other sense organs toward the central nervous system. (2) Efferent

neurons carry messages from the central nervous system in an outward direction-ordering muscles to contract and directing the activity of the body's organs and glands. (3) Interneurons, which are the most numerous, connect only with other neurons. Every moment of our lives, day and night, afferent neurons carry information to the brain and efferent neurons dispatch the brain's decisions and directions. At the center of this ceaseless activity of the nervous system, the interneurons of the brain and spinal cord perform all the essential functions that maintain our lives-and, in some as-yet-undetermined way, provide the basis for "mind."(a) A doctor is examining

a soccer player who was injured while trying to block a goal kick. The patient reports that he feels no sensation in his hand-even when the doctor pushes hard on the skin with an instrumentbut he can pick up a ball and throw it a good distance. Which neurons-afferent or efferent-are likely to have

The Cerebral Cortex and How It Makes Us HumanIf the top of a person's head were transparent and you looked down from above, you would see the brain as shown in Figure 2.5: a mass of tissue so rich in blood vessels that it takes on a pinkish cast. It resembles a rather large walnut, but it is soft and pulsing with life. This is the part of the brain that is chiefly responsible for thinking, remembering, and planning-the activities that make humans more intelligent than other animals. It is called the cerebral cortex, and nature has made it larger in proportion to body size in human beings than in other species. As can be seen in Figure 2.6, it would be too large to fit into the human skull if it didn't have convolutions-the intricate foldings and refoldings apparent in Figure 2.5. What you see in the photograph is in fact only about a third of the cerebral cortex. The rest is hidden in the creases. The cortex (from the Latin word for "bark") is actually the outer surface, about one-eighth of an inch (3 mm) thick, of the brain's largest single structure, the cerebrum. As illustrated in Figure 2.5, the cerebrum is split down the middle into a left half, or left hemisphere, and a right half, or right hemisphere. Although the two hemispheres look like mirror images, they differ slightly in form and are often engaged in different activities-it is almost as if we had two brains. This arrangement has provoked a number of fascinating questions, to which we return later in the chapter.

been affected by the injury?

Interneuron A eNS neuron that carries messages between neurons. Cerebral cortex Among its many other functions, the part of the brain responsible for thinking, remembering, and planning. Cerebrum The large brain mass that is covered bV the cerebral cortex.

~ [email protected]

FIGURE 2.S A top view of the human brain. Note especiallv the vertical line, resembling a narrow ditch, that runs down the middle from the right of the photo (the front of the brain) to the left. This deep fissure divides these upper areas of the brain into two separate halves, called hemispheres.

How the Brain Restores Its FunctionsWe have all heard about cases in which surgeons have reattached severed fingers and toes, which then regained their function. Although similar feats have not yet been accomplished in the damaged human brain and its connecting neural fibers, there is evidence that the brain and its functions can undergo renewal-and that they can sometimes be helped to do so. Following harm to some areas of the brain, adjoining areas may eventually appropriate a number of the lost functions. The healthy neighboring neurons may make up for the loss by forging new connections that substitute for those that were erased. As we grow older, for example, the dendrites of certain neurons increase in length, allowing them to receive messages despite the age-related destruction of neighboring neurons (Selkoe, 1992). And there is now considerable evidence-based largely on functional brain imaging research-that areas of the brain's cortex can shift their functions when neural pathways connected to them are damaged (Hallett, 2001; McEwen, 2000; Pizzamiglio, Galati, & Committeri, 2001; Stiles, 2001). From a different perspective, numerous studies over the past couple of decades have demonstrated that, at least with rats and mice, grafting healthy normal tissue or genetically modified tissue to damaged areas of the brain can restore or at least improve cognitive functioning in the affected areas (e.g., Kim et aI., 2001; Rolobos et aI., 2001; Tarricone, Simon, Li, & Low, 1996; Triarhou, 1995). It has also been known for some time that the brain is generally less likely to reject newly grafted tissue than are body organs (Wyatt & Freed, 1983). What are the prospects for restoring behavioral functions and health through such research? Techniques remain experimental, and considerable research is still necessary before new technologies can be widely applied. But the possibilities are there, including transplantation of tissue to portions of the brain affected in the neurological disorder known as Parkinson's disease (Olson et aI., 1998) and restoration of tissue that produces brain chemicals to treat Alzheimer's disease (Aisen & Davis, 1997) and schizophrenia (Jaber, Robinson, Missale, & Caron, 1996). Perhaps we are truly on the threshold of an era in which research on the operations of the brain will be translated into enormous help for millions of incapacitated people.

Beneath the cerebrum, and totally hidden when the brain is viewed from above, lie a number of other structures with their own special functions. We share many of these structuresfor example, structures that maintain basic life functions-with other forms of animal life. But it is the cerebrum and its cortex, comprising 80% of the human brain, that make us special. Without them, we would be "almost a vegetable, speecWess, sightless, senseless" (Rubel & Wiesel, 1979). Because of the brain's vast and complex responsibilities, injury to it-for example, from a hard blow to the head or from a bullet-can critically affect vital psychological and physical functions. For the most part, damage to the brain is permanent. In contrast to some neuFIGURE 2.6 The surprising size of the brain's cerebral cortex. rons in the PNS, such as motor neurons, the If it Were laid flat with its manv folds "ironed out," the cortex would neurons of the CNS do not regenerate (e.g., measure about 1.5 square feet 10.14 square meter) in area IOrnstein & Nicholls et al., 2001). Once CNS neurons sufThompson, 1984). fer damage, they are gone for good and with them whatever behavioral functions they made possible. Nevertheless, neuroscientists continue to study the brain's plasticity-its flexibility and power to rePlasticity organize and shift functions. Their work is discussed in Psychology in the Lab The power of the brain to and in Life. reorganize and shift functions.

HOW NEUROSCIENTISTS THE BRAIN AND MIND

STUDY

Neuroscience-especially cognitive neuroscience-is a fusion of various areas of psychology, including cognitive and FOCUS QU ESTIONS experimental psychology, neuropsychology, psychophysiology, developmental psychology, and clinical psychology, plus other disciplines such as neurology, neurobiology, and How do neuroscientists measure electrical changes biophysics (Muller & Mayes, 2001). As indicated in Chapand what do they tell us? ter 1, the role of psychology in this family of sciences has grown considerably in recent years, focusing on mental and physical functions of the brain. Scientific research on the structure and functions of the brain dates back to the 19th century, when it took the form of studying changes in behavior that were attributable to known brain damage. A later and much more systematic approach was electrical brain stimulation (EBS) , in which tiny harmless electrical charges are delivered to specific areas of the exposed cortex to see what thoughts or other behaviors they evoke. Foremost among the early neuroscientists who "mapped" the human brain in this fashion was Wilder Penfield (1891-1976), who did much of his research while performing neurosurgery to alleviate severe epilepsy. (Perhaps needless to say, invasive procedures such as EBS are not performed except as an adjunct to necessary brain surgery, greatly limiting this approach.) Nowadays, neuroscientists (and neurosurgeons) use much more sophisticated and much less invasive instrumentation and methods, which are opening up entire new realms in our understanding of how the brain works. It is safe to predict that the shift to these techniques will also reduce the need for research on laboratory animals in which various brain structures are deliberately lesioned (cut) or otherwise destroyed so that researchers can observe what happens to behavior. The findings on brain structures and functions presented in this chapter and at other points in the text are based on both the physiological research of the past and the brain imaging research of the present. Much of the latter began during the 1990s, which has been heralded as "the decade of the brain" (see Wagemans, Verstraten, & He, 2001).

Structural

Brain ImagingComputerized tomography(CT) A structural brain imaging method that uses X-rays to produce two-dimensional images.

A major breakthrough in brain imaging was computerized tomography (CT), or CATscanning, which developed out of the traditional X-ray procedure. In CT, brief bursts of X-rays are sent through the brain as the scanning apparatus rotates around the participant's head. The X-rays are "absorbed" differently depending on the density of the tissues, which means that different intensities of X-rays pass through to the film on the other side and the exposure varies accordingly. Computer processing then yields a series of tomograms, or visual "slices" of the brain along different planes, revealing many of its structures as well as tumors or other brain damage. CT has limited resolution, however; the images are fuzzy, and small structures are hard to see. Much more detailed pictures can be obtained through magnetic resonance imaging (MRI), which can produce either flat or three-dimensional images of the brain from any angle-again, through computer processing. Here, however, the brain's tissues are exposed to harmless magnetic fields and pulses of radio-frequency waves, which make their atoms "resonate" and give off magnetic energy. This energy is recorded by a special detector coil placed around the head of the participant or patient (Gazzaniga, Ivry, & Mangun, 1998; Oldendorf & Oldendorf, 1988).

Magnetic

resonance

imaging

(MRI)A structural brain imaging method that uses the magnetic properties of brain tissue to produce two- or threedimensional images.

Functional

Brain Imaging

Positron emission tomography (PET) A functional brain imaging method that uses the brain's metabolism of substances containing radioactive isotopes to produce ongoing brain images.

Functional magnetic resonance imaging (fMRI) A functional brain imaging method that uses the brain's natural metabolism of oxygen to produce ongoing brain images.

Both CT and traditional MRl have the disadvantage that they produce still pictures, which provide considerable information about brain structures but do not tell us anything about their functioning. This led researchers to develop additional approaches that can assess what the brain is doing. Positron emission tomography (PET) was the first of these approaches, arriving on the scene in the 1980s (Beatty, 2001). PET takes advantage of neural cell metabolism with regard to glucose (the form of sugar that the brain uses for energy). For example, glucose treated with minute amounts of a radioactive isotope may be injected into the participant's bloodstream. A good portion of it travels to the brain, where it is broken down primarily by clusters of neural cells that are actively engaged in processing, setting off chemical chain reactions that are picked up by special detectors placed around the head. Computer enhancement then yields ongoing displays of the areas of the brain that are active when the participant is exposed to different stimuli or asked to engage in different kinds of thought, as illustrated in Figure 2.7. The images occur almost in real time; there is a delay of just a minute or two because of the time required for the metabolism to occur (Purves et aI., 1997; Savoy, 2001). Another-and currently the most promising-approach is functional magnetic resonance imaging (fMRI), which has several advantages over PET (Savoy, 2001). With fMRI, precision detectors measure and localize minute magnetic changes that occur when oxygen is naturally metabolized by active clusters of neural cells. No radioactive substances are necessary, making this approach completely noninvasive. It produces ongoing images similar to those in Figure 2.7, except that it allows finer resolution than PET and also faster displays-a delay of seconds rather than minutes (Purves et aI., 1997). Even so, the finest resolution possible is on the order of millimeters and reflects the activity of perhaps several hundred thousand neurons that aren't necessarily engaged in related activities (Grill-Spector & Malach, 2001). Thus, researchers are continuing to pursue methods that would produce ever finer measures. In the future, researchers are expected to extend the uses of functional brain imaging beyond such current applications as mapping and understanding the

FIGURE 2.7 The brain in action. These PET scans reveal how various portions of the brain are activated while a participant is performing a series of verbal tasks. They reveal that blood flow shifts to different areas of the brain according to the type of task being performed.

brain. The ethical implications of brain imaging and other neuroscience techniques in the not-too-distant future are considered in Psychology and the Media.

,

Neuroscience in the FutureThe potential for improving people's lives through techniques derived from neuroscience research is undeniable. Brain imaging, for ex~ ample, has long been used in identifying brain damage and shedding light on mental disorders. Drugs that improve memory in people with amnesia are on the horizon, and someday it may be possible to "cure" Alzheimer's disease. The list of possible benefits goes on and on. But there is also the potential for misuse of neuroscience research, a subject pondered by leading neuroscientists, bioethicists, and other concerned professionals at the first-ever conference on "neuroethics," held in San Francisco in May 2002. The following are excerpts from an overview by William Safire (2002a), New York Times columnist and chairman of the board of directors of the conference's sponsor, The Dana Foundation (www.dana.org). Neuroethics, in my lexicon, is a distinct portion of bioethics, which is the consideration of good and bad consequences in medical practice and biological research. But the specific ethics of brain science hits home as no other research does in any other organ. It deals with our consciousness, our sense of self, and as such is central to our being. What distinguishes us from each other beyond our looks? Answer: our personalities and behavior, and these are the characteristics that brain science will soon have the ability to change in significant ways. Let's face it: one person's liver is pretty much like another .... Our brains, on the contrary, give us our intelligence and integrity, our curiosity and compassion, and-here's the most mysterious one-our conscience .... Zach [W. Hall, a prominent neuroscientist] has made the point to me that when we examine and manipulate the brain-unlike the liver ... whether for research, for treatment of disease, or for more sinister personal or political ends, we change people's lives in the most personal and powerful way. The misuse or abuse or failure to make the most of this power raises ethical challenges unique to neuroscience. In an article published after the conference (2002b), Safire articulated some of the ethical issues facing neuroscientists and those who will apply what neuroscientists discover how to do: For example, few will dispute the benefits of the regulated use of drugs to treat diseases of the brain. But what about drugs to enhance memory or alertness, to be taken before a test-isn't this akin to an athlete unethically taking steroids before a race? If we quiet the broadest range of inattentive, hyperactive children with compounds like Ritalin, do we weaken the development of adult concentration, character and self-control? How about a future use of imaging to pinpoint a brain area indicating a traumatic memory-should we expunge a victim's ability to recollect, say, a rape? Do we outlaw implantation of a memory of an event that never happened? Should brain imagers give law enforcement a "lie detector" far more reliable than the mechanical polygraph, and if so, is the reading of a mind of a resistant terrorist akin to torture? . . . [And] what of the hooking-up of software with what computerniks call "wetware" (the human nervous system) to combine human imagination with a machine's computational speed? Is this the next logical step of evolution, or an invitation to a controlling organization, as a NASAneuroethicist put it, "to hack into the wetware between our ears"? Our generation has outlived science fiction. Just as we have anti-depressants today to elevate mood, tomorrow we can expect a kind of Botox for the brain to smooth out wrinkled temperaments, to turn shy people into extroverts, or to bestow a sense of humor on a born grouch. But what price will human nature pay for these nonhuman artifices? What does the flattening of people's physical and mental differences, accompanied by a forced fitting of mental misfits, do to the diversity of personality that makes interpersonal dynamics so fascinating? Safire's article was aptly titled "The But-What-If Factor." Neuroscience is advancing at a geometric pace, and the potential benefits defy the imagination. At the same time, each step forward may indeed have an unsettling "But what if ... " attached to it.

ElectroencephalographvElectroencephalographv lEES)A method of measuring overall brain electrical activity using electrodes placed on the scalp.Electroencephalography (EEG), in which a few electrodes are placed on the scalp to measure relatively global brain wave patterns, has been around for many years. EEG, for example, has long been the standard measure of overall brain activity during different states of consciousness and stages of sleep (see Figure 8.5 on page 305). More recently, however, researchers have refined this approach by greatly increasing the number of electrodes, standardizing their locations by fitting them into a skull cap, and subjecting the much more specific measurements to computer analysis-yielding what is now called quantitative electroencephalography (QEEG). QEEG allows assessment of the tiny voltage fluctuations in the brain, known as event-related potentials (ERPs), that result, for example, from sensory stimuli such as sights and sounds (see Friedman, Cycowicz, & Gaeta, 2001). ERPs are studied in their own right-for example, to assess brain activity when there is no corresponding overt behavior or to assess infants' perceptual capabilities (e.g., see de Haan, Pascalis, & Johnson, 2002). ERPs also can be localized in the brain and increasingly are being used in conjunction with procedures such as fMRI, because the time delay in their occurrence is on the order of milliseconds (Wilding, 2001). That is, ERPs can be used as "time markers" when crossreferenced with fMRI images. As with functional imaging, we can predict that QEEG and variations on this method will continue to be refined.

(b)

Would a researcher en-

gaged in neuroscience be more likely to study the role of genetics or of brain chemistry in cognitive development? (c) If researchers wanted to

know what portions of your brain were especially active when you tried to remember a set of facts, what brain imaging technique or techniques would they be most likely to use?

THE BRAIN'S FUNCTIONS, I: EXPERIENCING THE WORLDYou're driving down the street and a child darts into the path of your car. In a twinkling, the muscles of your leg tense and your foot hits the brake, bringing your car safely to a stop. Or, you're What brain structures process incoming sensory sound asleep, when suddenly there are shouts of "Fire!" You stimulation? awake with a start, jump up, and dash to safety. What brain structures initiate and coordinate body Although we tend to take our behavior in such situations movements? for granted, it is actually remarkable. Such acts require the teamwork of millions of neurons, receiving and sending messages with blinding speed. Our abilities to attend to information from the world, Quantitative process it, and respond to it all depend on the intricate functioning of the brainelectroencephalographv the cerebral cortex and the interrelated structures below it, as well as the brain's IQEES) links to the peripheral nervous system.

A method of assessing brain activity that uses a large array of electrodes in a skull cap to measure and localize minute electrical reactions of areas of the brain.

Sensing and Interpreting

the Environment

Somatosensory cortexThe specialized area of the cerebral cortex responsible for analyzing and interpreting messages from the sense organs.

Most of the information picked up by our senses-if we attend to it-is eventually transmitted to the cerebral cortex. The cortex has specialized areas, some of which are shown in Figure 2.8. It also contains a long strip known as the somatosensory cortex, which receives messages on touch from the feet (at the top) to the head (at the bottom). These specialized areas analyze and interpret incoming messages, allowing the brain to decide which messages are important and what they mean. The sounds of speech-which are of particular importance because language plays such a large role in human behavior-have an area of their own that is concemed with understanding the meanings of words and sentences.

Bodily movement

Primary hearing area

Understanding speech

Primary vision area

FIGURE 2.8 Some areas of the cerebral cortex with special functions. On thisdrawing of the cerebral cortex as it would be seen from the left side of the bodV, the areas known to be involved in specific functions are designated.Geschwind, 1979.

The importance of the cerebral cortex in registering and processing sensory information becomes dramatically clear in cases of damage to any of these portions of the brain. For example, depending on the location and extent of injury to the back part of the cortex, which is responsible for vision, an individual might suffer varying degrees of blindness, even though the eyes and their muscles and nerves remain intact. With damage to a different area of the cortex, a patient may be unable to recognize a familiar person's identity from his or her face but retain the capacity to recognize the person from his or her walk. Thus, different parts of the brain and different neural circuits appear to be responsible for acquiring different types and levels of knowledge about the same entity (Damasio, 1990). If the area for understanding speech is injured, an individual might no longer be able to interpret what is being said, even though all parts of the ear are healthy and the sounds of the words spoken are clearly heard. In such cases, the afflicted individuals seem to be incapable of getting the words "through their heads."

Processing and Transmitting

Sensory InformationThalamusThe brain's relav station for messages to and from the bodV.

Sensory information from the outside world is processed and organized in the lower parts of the brain a few milliseconds before it reaches the cortex. Serving as a relay station for sensory messages from the body to the cortex is the thalamus, which can be seen in Figure 2.9. (The thalamus also acts as a relay station for some of the messages traveling in the opposite direction, especially those calling for body movements, described in the next section.)

Thalamus----------------Hypothalamus

---------------Reticular activating system

FIGURE 2.9 A sectional

view of the brain.

Parts of the human brain are shown here as they would be seen if the brain were sliced down the middle from front to back. The inset shows a photograph of the brain taken from the same perspective.London, 1978. Inset courtesy of the Warder Collection.

Reticular activating

system

(RASIA network of neural cells in the brain stem that serves as a way station for messages from the sense organs.

Sensory information is also processed in a network of neural cells near the base of the brain called the reticular activating system (RAS). This structure gets its name from its appearance under a microscope as a criss-crossed (reticulated) pattem of neural fibers. As shown in Figure 2.9, it extends downward to the brain stem, where the brain and spinal cord join. Nerve pathways carrying messages from the sense organs to the cerebrum have side branches in the RAS. These stimulate the system to send its own neural impulses upward to the cerebrum, arousing it to a state of alertness and activity. Animals whose RAS has been destroyed remain permanently comatose for lack of such arousal. If the RAS is electrically stimulated, sleeping animals will awaken immediately (Rosenzweig & Lieman, 1982). The RAS also helps us focus selectively on those sensory signals that are most important. For example, when you are reading a newspaper, the RAS blocks unimportant messages-the sounds in your room or flashes of lightning outside-and prepares the cortex to receive the ones that matter.

Generating

Body Movements(d) On March 30, 1981, James Brady, press secretary to President Ronald Reagan, was shot above the left eye by would-be assassinJohn Hinckley. The bullet went through Brady's brain and lodged in the right hemisphere. Why is it unlikely that Brady will ever fully recover his lost abilities to function-for instance, to walk, speak, and express himself as as he did before the shooting? (e) Is a combat soldier who

Sometimes the reactions of the nervous system are immediate-as when you quickly move your hand away from a hot stove. Such responses do not require commands from the brain. Instead, they are processed by connections in the spinal cord, as are many basic reflexes, referred to as involuntary. But the movements you make deliberately-from the gross muscular adjustments of the arms and legs when lifting things or running to the tiny adjustments of finger muscles when threading a needle or playing a guitar-are initiated in the cerebral cortex. The actual sequence of events in the brain that results in voluntary movements is complex and not yet completely understood, but we do know that many parts of the brain are engaged in the process. A specialized strip on the cortex (Figure 2.8) controls body movements from feet to head. Known as the motor cortex, it initiates body movements in response to orders from other parts of the brain. In the case of the simple act of picking up a glass, for example, you must first have the intention of performing the act before actually executing the action (Libet, 1985). The motor eortex also has an area for speaking, which moves the vocal folds and muscles associated with them in a way that produces meaningful sounds. When a stroke or other injury damages this area of the cortex, the result is often loss of the ability to formulate and utter words that convey ideas. This portion of the brain also manufactures the sounds that give voice to feelings-a shriek of delight when you see your home team score, a groan of despair when you hear about the death of a friend, or a sigh of contentment when you feel the embrace of a loved one.

suffers a gunshot wound to the back of the brain more likely to have problems speaking or seeing? (f) Why is a perfectly func-

tioning cerebellum so important to both a guitar player and a ballet dancer?

Managing Coordination

and BalanceMotor cortexThe specialized strip on the cerebral cortex that controls body movements.

As shown in Figure 2.9, below the cerebrum and attached to the back of the brain stem is a bulging structure that looks like a tree in full bloom. Called the cerebellum, it is essential for many aspects of movement. The cerebellum, which has been called a "magnificently pattemed, orderly and fantastically complex piece of machinery" (Rubel, 1979), has many connections with parts of the cerebral cortex that initiate muscular activity. One of the special roles of the cerebellum is to coordinate all the finely regulated muscular movements we are capable of, such as playing a musical instrument or manipulating a small tool. If the cerebellum is damaged, movements become jerky, and great effort and concentration are required to perform even activities that were once automatic, such as walking. Victims of damage to the cerebellum have difficulty speaking, which requires well-coordinated movements of the muscles of the vocal cords, windpipe, and mouth. The cerebellum also controls body balance and is the part of the brain that keeps us right side up. It plays an important role in allowing us to do things that require great equilibrium. An example is shooting a pistol at a target. Studies of champion marksmen in the Russian army showed that, although many parts of their body moved, the pistol remained virtually immobile (Evarts, 1979). With millions of neurons sending their billions of messages to and fro-from the eyes, the cerebral cortex, the arms and fingers-somehow the brain, thanks largely to the cerebellum, is able to integrate all these messages into an act of exquisite balance and precision. Like the cerebrum, the cerebellum is divided into two lobes, or hemispheres. The left and right lobes are connected by the pons, which gets its name from the Latin word for "bridge." The neurons of the pons transmit messages between the two hemispheres of the cerebellum.

CerebellumA brain structure involved in controlling balance and movement.

Pons The brain structure connecting the two hemispheres of the cerebellum.

THE BRAIN'S FUNCTIONS, II: OVERSEEING EMOTIONS AND SURVIVALThe remarkable feats of the brain described thus far, which allow us to make sense of our environment and move about in the world, are impressive in their own right. But even with them, our lives What brain structures are involved in experiencing would be flat and barren were it not for the deeply moving expeemotions? riences we call emotions. True, emotions such as fear and anger How are our body functions regulated to keep us are often upsetting and sometimes destructive. However, they alive? also help us cope with the world and meet its crises, motivating us to action. Other emotions, such as love and joy, greatly enrich our lives. All these feelings are produced by the brain working in concert with the body. (The components of an emotion, such as the physiological changes and the conscious or unconscious experiences that accompany them, are discussed in detail in Chapter 8.) The brain not only regulates our emotions; it also ensures our physical survival by keeping our bodies in healthy working order. It oversees the fundamental functions of breathing, pumping blood, and maintaining adequate blood pressure. It tells us when we need food or drink, and it keeps our body chemistry in balance. The brain seems to watch out for our survival as a species, too; it is deeply involved in sexual development and behavior. Our lives end only when the brain ceases its last flicker of activity.

Limbic system The set of interconnected structures and pathways in the brain involved with emotion and memory.

The Wellsprings

of Passions and Feelings

Of special importance in emotional life is a network of structures and pathways near the center of the brain known as the limbic system. It makes up about onefifth of the brain (see Figure 2.10).

FIGURE 2.10 The brain'slimbic system. Limbic means "bordering," and the limbic system is so named because its parts form a border or loop around the deepest core of the cerebrum. Because it is in close contact with both the frontal lobes of the cortex and the brain stem, the limbic system is strategically located for its role in vital brain functions.

The limbic system consists of many components, Right amygdala one of which-the hippocampus-plays a primary role ..J Left amygdala in memory, as discussed later in the chapter. In effect, the hippocampus receives information and "decides" whether the information is familiar or unfamiliar. If it is unfamiliar-and therefore potentially significant or threatening-another structure, the amygdala, comes into play. The amygdala has neurons that are connected to other parts of the brain and body. The activity of these parts leads to the experience of intense emotions such as anger and fear (Davis, 1997). Through its connections with other portions of the brain, particularly the areas associated with taste and smell, the amygdala can also trigger actions that are appropriate to a positive emo2 tional state-in response, say, to good food (Rolls, 2000). Monkeys In one experiment, researchers showed that the startle reaction of rats in response to a sudden, very FIGURE 2.11 The amygdala and pain'ul emotion. When loud noise is greater when the rats have been condisquirrel monkeys were placed in a room where they had extioned to fear a shock in advance of the noise. That is, perienced earlier shock, the increase in delta waves-slow the state of fear leads to a larger startle response. But brain waves that typically emerge during extreme emotional when the amygdala is surgically removed, the exagarousal-was more marked in the right amygdala than in gerated startle response produced by the fear vanishes, the left. demonstrating that the amygdala mediates the fear exAdapted from Lloyd & Kling, 1991. perience (Hitchcock & Davis, 1991). As portrayed in Figure 2.11, it is the right amygdala, rather than the left, that is especially activated when fear is present. (As discussed later, the right hemisphere of the brain is especially involved in regulating Amygdala negative emotions.) The part of the limbic system The limbic system includes another key player in our emotional lives and our that plays a role in intense physical survival: the hypothalamus, the brain's most direct link to the glands that positive or negative emotions. are active in fear, anger, and other emotions. The hypothalamus is attached to the Hypothalamus "master gland," the pituitary gland (see Figure 2.9, p. 64), which it partly controls. The portion of the limbic sysThe pituitary gland is one of the endocrine glands, discussed below. Working in tem that serves as a mediator concert with other portions of the limbic system and the cortex, the hypothalabetween the brain and the mus delivers messages that help produce the "stirred up" bodily processes that acbody and helps control metabcompany emotion. olism, sleep, hunger, thirst, In lower mammals, the limbic system appears to contain the programming body temperature, sexual bethat directs the instinctive behaviors involved in feeding, mating, fighting, and eshavior, and emotions. caping from danger. There is evidence that when animals learn to anticipate that a stressful experience-such as a shock-is coming, the limbic system becomes Pituitary gland active (Herrmann, Hurwitz, & Levine, 1984). Laboratory experiments have shown The master endocrine gland, that surgery on or electrical stimulation of various parts of the limbic system can which secretes hormones concause animals to behave in unusually docile or unusually aggressive ways. Damtrolling growth and sexual age to one part of the limbic system will reduce the fear and avoidance that many development at puberty and animals display when faced with a novel stimulus; damage to another part will reregulating other endocrine move inhibitions on attack behavior and make many animals vicious. glands.

Staying Alive and Physiologically

in Tune

The body's well-being depends on keeping its many functions on a reasonably even keel, despite the numerous events and environmental changes it continually encounters. For example, the body must keep its intemal temperature stable through all seasons and levels of exertion, and it must maintain a proper supply of oxygen, water, and various other substances that cells need to function well. The state of dy-

These photographs show the effect of electrical stimulation of the brain of a cat through electrodes planted in or around the limbic system. At left, under stimulation at one particular spot, the cat calmly ignores its traditional prey, the rat. At right, stimulation at another spot makes the cat assume a hostile posture toward a laboratory assistant with whom it is ordinarily on friendly terms.

Homeostasis A state of equilibrium, or balance, in the physiological systems within the human body.

Medulla The structure in the brain stem that helps regulate breathing, heartbeat, blood pressure, and digestion.

namic equilibrium achieved when these processes are working right and all physiological systems are balanced is called homeostasis. The air we breathe, the water we drink, and the foods we eat are the raw materials required to keep our cells properly supplied and working correctly. We need a central management system to order these supplies, make sure they arrive on time, distribute them where they are needed, and see that they are processed properly. The brain provides that management. Besides being a center for emotional behavior, the hypothalamus helps maintain homeostasis by signaling when the body needs more food or water and by regulating states of wakefulness and sleep. It also acts like a highly accurate thermostat, keeping body temperature normal by reacting to messages from temperature sensors in the skin and from its own temperature-sensing cells. Our continuing survival depends as well on the medulla, which can be seen in Figure 2.9 (p. 64). This structure in the brain stem is responsible for coordinating vital bodily processes such as breathing, heartbeat, blood pressure, and digestion.

The Autonomic Nervous System: The Brain's Busy DeputyAutonomic nervous system (ANS) The neural network connecting the central nervous system with glands and smooth muscles, involved in maintaining homeostasis. Endocri ne glands Glands that discharge hormones directly into the bloodstream, bringing about a variety of physiological and psychological changes.In controlling bodily processes, the brain has an effective assistant in the form of the autonomic nervous system (ANS). The word autonomic means independent or self-sufficient, and in many ways the autonomic nervous system does operate on its own, without much, if any, conscious control. Unless we are hooked up to biofeedback equipment that tells us what our body is doing (see Chapter 12), we cannot command our stomach muscles to make the movements that help digest food, nor can we order the muscles of the blood vessels to redirect the flow of blood toward the muscles of the arms or legs when we have to do physical work. But the ANS can do all these things and does so constantly, even when we are asleep. In addition, the ANS exercises considerable independent influence on important bodily structures called endocrine glands-glands of internal secretionwhich are also resistant to conscious control. Unlike the sweat glands that deliver perspiration to the skin or the salivary glands that deliver fluids to the mouth, the endocrine glands discharge their products directly into the bloodstream. These biochemical substances, as noted earlier, are called hormones. They influence many body processes, including those associated with emotional behavior. As illustrated in Figure 2.12, the endocrine glands include the pineal, pituitary, parathyroid, thyroid, and adrenal glands, as well as the pancreas, ovaries, and testes. The autonomic nervous system exerts its influence on important body processes through a number of centers called ganglia, as shown in Figure 2.13. These

_______ --------

Pineal: affects sleep-waking

rhythms and mood

Pituitary: master gland that triggers and regulates actions of other glands; controls early physical growth and activates sex glands at puberty Parathyroids: maintain normal state of excitability of the nervous system

A/~---

Thyroid: controls rate of metabolism (the rate at which food is burned to provide energy) and thus influences level of body activity, temperature, and weight

Adrenals: stimulate the body by producing the hormones epinephrine and norepinephrine at times of emergency or fear, and by producing the hormone noradrenaline at times of great physical effort or anger ~-----Pancreas: governs the level of blood sugar

~

Ovaries: (in female): stimulate development of secondary sex characteristics such as breasts at puberty; control bodily processes during menstrual cycle and pregnancy

~--------Testes:

(in male): regulate development of secondary such as facial hair; generate sexual arousal

sex characteristics

are like small brains scattered throughout the body. They consist of masses of neural cells packed together and connected with one another-as in the brain itself, but on a much smaller scale. Some of these neurons have long fibers over which they send commands to the glands, the heart muscles, and the muscles of the body's organs and blood vessels. Others are connected to the brain and the spinal cordwhich means that the ANS, though independent in many ways, does take some orders from above. For example, if you are wakened by shouts of "Fire!" your ears send a message to your brain, which then sends an emergency command to the ANS, which in turn springs into action through its various connections to the glands and muscles. As is also shown in Figure 2.13, there are two divisions of the ANS, which differ in structure and function: the parasympathetic and the sympathetic.

FIGURE 2.12 The human endocrine glands. The endocrine glands receive messages from the brain and ANS that tell them to speed up or slow down hormone production. TheV influence the excitabilitv of the brain and the rest of the nervous system and are directlv involved, for example, in emotional experiences. Parasvmpathetic division of the ANS A part of the nervous system made up of scattered ganglia near the glands or the muscles of organs. It helps maintain functions such as heartbeat and digestion.

The Parasvmpathetic Division: Running the Ordinarv Business of Living The parasympathetic division of the ANS is connected to the stem of the brain and the lower part of the spinal cord. It is made up of a number of widely scattered ganglia, most of which lie near the glands or muscles of organs to which it delivers its messages. Because it is so loosely constructed, it tends to act in piecemeal fashion, delivering its orders to one or several parts of the body but not necessarily to all at once. In general, the parasympathetic division plays its most important role during those frequent periods when no danger threatens and the body can relax and go about the ordinary business of living. It tends to slow down the work of the heart and lungs. It aids digestion by stimulating the salivary glands, producing wavelike motions of the muscles of the stomach and intestines, and encouraging the stomach to produce digestive acid and the liver to produce the digestive fluid called bile. It also brings about elimination of the body's waste products from the intestines and bladder. At times, however, the parasympathetic division abandons these usual tasks and helps mobilize the body for emergency action. When it does thisoperating in ways that are not yet understood-it seems to assist and supplement the work of the other part of the autonomic system, the sympathetic division.

FIGURE 2.13 The autonomic nervous system. Along chain of ganglia of the svmpathetic svstem extends down each side of the spinal cord lone side is shown here). The parasvmpathetic svstem has ganglia near the glands and smooth muscles that both divisions of the ANS Spinal cord-help control, although in different wavs.Adapted from Crosby, Humphrey, & Lauer,

1962.

Sympathetic Parasympathetic ----

Sympathetic division of the ANSlong chains of ganglia that extend down the sides of the spinal cord and activate glands and smooth muscles for "fight" or "flight."

The Sympathetic Division: Meeting Emergencies The sympathetic division of the ANS is shown in Figure 2.13 as a long chain of ganglia extending down the side of the spinal cord. There is a similar chain, not shown, on the other side of the cord. All the many ganglia of the sympathetic division are interconnected. Note that many of the neural fibers going out from the chains of ganglia meet again in additional ganglia in other parts of the body, where they again form complex interconnections with neural cells that finally carry commands to the glands and smooth muscles. For this reason, the sympathetic division, unlike the parasympathetic division, tends to function as a unit. When the sympathetic division springs into action, as it does when we experience fear or anger, it does many things all at once. Most notably, it commands the adrenal glands to spill their powerful stimulants-such as norepinephrine, discussed later in the chapter-into the bloodstream. By acting on the adrenal glands, liver, and pancreas, it increases the level of blood sugar, thus raising the rate of metabolism and providing additional energy. It causes the spleen-a glandlike organ in which red blood cells are stored-to release more red blood cells into the bloodstream and thus enables the blood to carry more oxygen to the body's tis-

sues. It changes the size of the blood vessels, enlarging those in the heart and the muscles that control body movement and constricting those in the muscles of the stomach and intestines. It makes the lungs breathe harder. It enlarges the pupils of the eyes, which are controlled by muscles, and slows the activity of the salivary glands. ("Wide eyes" and a dry mouth are characteristic of strong emotions such as fear.) It also activates the sweat glands and contracts the muscles at the base of the hairs on the body, producing gooseflesh in humans and causing the hair on furry animals to rise. In general, the changes triggered by the sympathetic division prepare the body for emergency action, such as fighting or running away. Clearly, there is a very close marriage between the brain and the body, linked together as they are through numerous physical and chemical connections. The implications of this link for our state of mind, emotions, and physical and mental well-being are discussed throughout this book.

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