Origins of Behavioral Neuroscience: Ethical Issues and Research with Animals, Summaries of Neuroscience

Download Origins of Behavioral Neuroscience: Ethical Issues and Research with Animals and more Summaries Neuroscience in PDF only on Docsity! OUTLINEOrigins of Behavioral Neuroscience1 chapter ● Understanding Human Consciousness: A Physiological Approach Split Brains ● The Nature of Behavioral Neuroscience The Goals of Research Biological Roots of Behavioral Neuroscience ● Natural Selection and Evolution Functionalism and the Inheritance of Traits Evolution of the Human Species Evolution of Large Brains ● Ethical Issues in Research with Animals ● Careers in Neuroscience ● Strategies for Learning LEARNING OBJECTIVES 1. Describe the behavior of people with split brains and explain what study of this phenomenon contributes to our understanding of self-awareness. 2. Describe the goals of scientific research. 3. Describe the biological roots of behavioral neuroscience. 4. Describe the role of natural selection in the evolution of behavioral traits. 5. Describe the evolution of the human species. 6. Discuss the value of research with animals and ethical issues concerning their care. 7. Describe career opportunities in neuroscience. 8. Outline the strategies that will help you learn as much as possible from this book. ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 1 PROLOGUE René’s Inspiration René, a lonely and intelligent young man of eighteen years, had secluded himself in Saint- Germain, a village to the west of Paris. He recently had suffered a nervous breakdown and chose the retreat to recover. Even before coming to Saint-Germain, he had heard of the fabulous royal gardens built for Henri IV and Marie de Médicis, and one sunny day he decided to visit them. The guard stopped him at the gate, but when he identified himself as a student at the King’s School at La Flèche, he was permitted to enter. The gardens con- sisted of a series of six large terraces overlooking the Seine, planted in the symmetrical, orderly fashion so loved by the French. Grottoes were cut into the limestone hillside at the end of each terrace; René entered one of them. He heard eerie music accompanied by the gurgling of water but at first could see noth- ing in the darkness. As his eyes became accustomed to the gloom, he could make out a figure illuminated by a flickering torch. He approached the figure, which he soon recognized as that of a young woman. As he drew closer, he saw that she was actually a bronze statue of Diana, bathing in a pool of water. Suddenly, the Greek goddess fled and hid behind a bronze rosebush. As René pursued her, an imposing statue of Neptune rose in front of him, barring the way with his trident. René was delighted. He had heard about the hydraulically operated mechanical organs and the moving statues, but he had not expected such realism. As he walked back toward the entrance to the grotto, he saw the plates buried in the ground that controlled the valves operating the machinery. He spent the rest of the afternoon wandering through the grottoes, listening to the music and being entertained by the statues. During his stay in Saint-Germain, René visited the royal gar- dens again and again. He had been thinking about the rela- tionship between the movements of animate and inanimate objects, which had concerned philosophers for some time. He thought he saw in the apparently purposeful, but obviously inanimate, movements of the statues an answer to some impor- tant questions about the relationship between the mind and the body. Even after he left Saint-Germain, René Descartes revis- ited the grottoes in his memory; he went so far as to name his daughter Francine after their designers, the Francini broth- ers of Florence. 2 The last frontier in this world—and perhaps the greatest one—lies within us. The human nervous system makes possible all that we can do, all that we can know, and all that we can experience. Its complexity is immense, and the task of studying it and understanding it dwarfs all previous explo- rations our species has undertaken. One of the most universal of all human characteristics is curiosity. We want to explain what makes things happen. In ancient times, people believed that natural phenomena were caused by animating spirits. All moving objects—animals, the wind and tides, the sun, moon, and stars—were assumed to have spirits that caused them to move. For example, stones fell when they were dropped because their ani- mating spirits wanted to be reunited with Mother Earth. As our ancestors became more sophisticated and learned more about nature, they abandoned this approach (which we call animism) in favor of physical explanations for inanimate moving objects—but they still used spirits to explain human behavior. From the earliest historical times, people have believed that they possessed something intangible that animated them: a mind, a soul, or a spirit. This belief stems from the fact that each of us is aware of his or her own existence. When we think or act, we feel as though something inside us is thinking or deciding to act. But what is the nature of the human mind? We have physical bodies with muscles that move them and sensory organs such as eyes and ears that perceive information about the world around us. Within our bodies, the nervous system plays a central role, receiving information from the sensory organs and controlling the movements of the muscle—but what is the mind, and what role does it play? Does it control the nervous system? Is it a part of the nervous system? Is it physical and tangible, like the rest of the body, or is it a spirit that will always remain hidden? Behavioral neuroscientists take an empirical and practical approach to the study of human nature. Most of us believe that the mind is a phenomenon pro- duced by the workings of the nervous system. We believe that once we understand the workings of the human body—especially the workings of the nervous system— we will be able to explain how we perceive, how we think, how we remember, and ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 2 that this is so, we ask the patient to smell an odor with the right nostril and then reach for some objects that are hidden from view by a partition. If asked to use the left hand, controlled by the hemisphere that detected the smell, the patient will select the object that corresponds to the odor—a plastic flower for a floral odor, a toy fish for a fishy odor, a model tree for the odor of pine, and so forth. However, if asked to use the right hand, the patient fails the test because the right hand is connected to the left hemisphere, which did not smell the odor. (See Figure 1.3.) The effects of cutting the corpus callo- sum reinforce the conclusion that we become conscious of something only if information about it is able to reach the parts of the brain responsible for verbal communication, which are located in the left hemisphere. If the information does not reach these parts of the brain, then that information does not reach the conscious- ness associated with these mechanisms. We still know very little about the physiology of consciousness, but studies of people with brain damage are beginning to provide us with some useful insights. This issue is dis- cussed in later chapters. em Right hemisph Corpus callosum has been cut Left h isphere Control of left hand Control of speech Person denies smelling anything Left nostril is plugged Left hand chooses a rose Olfactory information Perfume with aroma of rose is presented to right nostril Understanding Human Consciousness: A Physiological Approach 5 FIGURE 1.3 Smelling with a Split Brain. An object is identified in response to an olfactory stimulus by a person with a split brain. Inter imSummar y Understanding Human Consciousness: A Psychological Approach The concept of the mind has been with us for a long time—probably from the earliest history of our species. Modern science has con- cluded that the world consists of matter and energy and that what we call the mind can be explained by the same laws that govern all other natural phenomena. Studies of the functions of the human nervous system tend to support this position, as the specific example of the split brain shows. Brain damage, by disconnecting brain functions from the speech mechanisms in the left hemisphere, reveals that the mind does not have direct access to all brain functions. When sensory information about a particular object is pre- sented to the right hemisphere of a person who has had a split-brain operation, the person is not aware of the object but can, nevertheless, indicate by movements of the left hand that the object has been per- ceived. This phenomenon suggests that consciousness involves oper- ations of the verbal mechanisms of the left hemisphere. Indeed, consciousness may be, in large part, a matter of our “talking to our- selves.” Thus, once we understand the language functions of the brain, we may have gone a long way to understanding how the brain can be conscious of its own existence. Thought Questions 1. Could a sufficiently large and complex computer ever be pro- grammed to be aware of itself? Suppose that someone someday claims to have done just that. What kind of evidence would you need to prove or disprove this claim? 2. Clearly, the left hemisphere of a person with a split brain is con- scious of the information it receives and of its own thoughts. It is not conscious of the mental processes of the right hemi- sphere. But is it possible that the right hemisphere is conscious too, but is just unable to talk to us? How could we possibly find out whether it is? Do you see some similarities between this issue and the one raised in the first question? ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 5 generalization Type of scientific explanation; a general conclusion based on many observations of simi- lar phenomena. reduction Type of scientific explana- tion; a phenomenon is described in terms of the more elementary processes that underlie it. 6 CHAPTER 1: Origins of Behavioral Neuroscience The Nature of Behavioral Neuroscience The modern history of behavioral neuroscience has been written by psychologists who have combined the experimental methods of psychology with those of physiol- ogy and have applied them to the issues that concern all psychologists. Thus, we have studied perceptual processes, control of movement, sleep and waking, repro- ductive behaviors, ingestive behaviors, emotional behaviors, learning, and lan- guage. In recent years, we have begun to study the physiology of human pathological conditions, such as addictions and mental disorders. The Goals of Research The goal of all scientists is to explain the phenomena they study. But what do we mean by explain? Scientific explanation takes two forms: generalization and reduc- tion. Most psychologists deal with generalization. They explain particular instances of behavior as examples of general laws, which they deduce from their experiments. For instance, most psychologists would explain a pathologically strong fear of dogs as an example of a particular form of learning called classical conditioning. Presum- ably, the person was frightened earlier in life by a dog. An unpleasant stimulus was paired with the sight of the animal (perhaps the person was knocked down by an exuberant dog or was attacked by a vicious one), and the subsequent sight of dogs evokes the earlier response: fear. Most physiologists deal with reduction. They explain complex phenomena in terms of simpler ones. For example, they may explain the movement of a muscle in terms of the changes in the membranes of muscle cells, the entry of particular chemicals, and the interactions among protein molecules within these cells. By contrast, a molecular biologist would explain these events in terms of forces that bind various molecules together and cause various parts of the molecules to be attracted to one another. In turn, the job of an atomic physicist is to describe mat- ter and energy themselves and to account for the various forces found in nature. Practitioners of each branch of science use reduction to call on sets of more ele- mentary generalizations to explain the phenomena they study. The task of the behavioral neuroscientist is to explain behavior in physiological terms—but behavioral neuroscientists cannot simply be reductionists. It is not enough to observe behaviors and correlate them with physiological events that occur at the same time. Identical behaviors may occur for different reasons and thus may be initiated by different physiological mecha- nisms. Therefore, we must understand “psycholog- ically” why a particular behavior occurs before we can understand what physiological events made it occur. Let me provide a specific example: Mice, like many other mammals, often build nests. Behavioral observations show that mice will build nests under two conditions: when the air temperature is low and when the animal is pregnant. A nonpregnant mouse will build a nest only if the weather is cool, whereas a pregnant mouse will build one regardless of the temperature. The same behavior occurs for differ- ent reasons. In fact, nest-building behavior is con- trolled by two different physiological mechanisms. Nest building can be studied as a behavior related to the process of temperature regulation, or it can be studied in the context of parental behavior. Studies of people with brain damage have given us insights into the brain mechanisms involved in language, perception, memory, and emotion. ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 6 The Nature of Behavioral Neuroscience 7 In practice, the research efforts of behavioral neuroscientists involve both forms of explanation: generalization and reduction. Ideas for experiments are stim- ulated by the investigator’s knowledge both of psychological generalizations about behavior and of physiological mechanisms. A good behavioral neuroscientist must therefore be both a good psychologist and a good physiologist. Biological Roots of Behavioral Neuroscience Study of (or speculations about) the physiology of behavior has its roots in antiquity. Because its movement is necessary for life and because emotions cause it to beat more strongly, many ancient cultures, including the Egyptian, Indian, and Chinese, considered the heart to be the seat of thought and emotions. The ancient Greeks did, too, but Hippocrates (460–370 B.C.) concluded that this role should be as- signed to the brain. Not all ancient Greek scholars agreed with Hippocrates. Aristotle did not; he thought the brain served to cool the passions of the heart. But Galen (A.D. 130–200), who had the greatest respect for Aristotle, concluded that Aristotle’s role for the brain was “utterly absurd, since in that case Nature would not have placed the encephalon [brain] so far from the heart, . . . and she would not have attached the sources of all the senses [the sensory nerves] to it (Galen, 1968 translation, p. 387). Galen thought enough of the brain to dissect and study the brains of cattle, sheep, pigs, cats, dogs, weasels, monkeys, and apes (Finger, 1994). René Descartes, a seventeenth-century French philosopher and mathemati- cian, has been called the father of modern philosophy. Although he was not a biol- ogist, his speculations about the roles of the mind and brain in the control of behavior provide a good starting point in the history of behavioral neuroscience. Descartes assumed that the world was a purely mechanical entity that, once having been set in motion by God, ran its course without divine interference. Thus, to understand the world, one had only to understand how it was constructed. To Descartes, animals were mechanical devices; their behavior was controlled by envi- ronmental stimuli. His view of the human body was much the same: It was a machine. As Descartes observed, some movements of the human body were auto- matic and involuntary. For example, if a person’s finger touched a hot object, the arm would immediately withdraw from the source of stimulation. Reactions like this did not require participation of the mind; they occurred automatically. Descartes called these actions reflexes (from the Latin reflectere, “to bend back upon itself”). Energy coming from the outside source would be reflected back through the ner- vous system to the muscles, which would contract. The term is still in use today, but of course we explain the operation of a reflex differently. Like most philosophers of his time, Descartes was a dualist; he believed that each person possesses a mind—a uniquely human attribute that is not subject to the laws of the universe. But his thinking differed from that of his predecessors in one important way: He was the first to suggest that a link exists between the human mind and its purely physical housing, the brain. He believed that the sense organs of the body supply the mind with information about what is happening in the environ- ment, and that the mind, using this information, controls the movements of the body. In particular, he hypothesized that the interaction between mind and body takes place in the pineal body, a small organ situated on top of the brain stem, buried beneath the cerebral hemispheres. He noted that the brain contains hollow chambers (the ventricles) that are filled with fluid, and he believed that this fluid is under pressure. In his theory, when the mind decides to perform an action, it tilts the pineal body in a particular direction like a little joystick, causing pressurized fluid to flow from the brain into the appropriate set of nerves. This flow of fluid causes the same muscles to inflate and move. (See Figure 1.4.) As we saw in the prologue, the young René Descartes was greatly impressed by the moving statues in the royal gardens (Jaynes, 1970). These devices served as models for reflex An automatic, stereotyped movement produced as the direct result of a stimulus. ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 7 functionalism The principle that the best way to understand a biologi- cal phenomenon (a behavior or a physiological structure) is to try to understand its useful functions for the organism. 10 CHAPTER 1: Origins of Behavioral Neuroscience Natural Selection and Evolution Müller’s insistence that biology must be an experimental science provided the start- ing point for an important tradition. However, other biologists continued to observe, classify, and think about what they saw, and some of them arrived at valu- able conclusions. The most important of these scientists was Charles Darwin. (See Figure 1.7.) Darwin formulated the principles of natural selection and evolution, which revolutionized biology. Functionalism and the Inheritance of Traits Darwin’s theory emphasized that all of an organism’s characteristics—its structure, its coloration, its behavior—have functional significance. For example, their strong talons and sharp beaks permit eagles to catch and eat prey. Most caterpillars that eat green leaves are themselves green, and their color makes it difficult for birds to see them against their usual background. Mother mice construct nests, which keep their offspring warm and out of harm’s way. Obviously, the behavior itself is not inherited—how can it be? What is inherited is a brain that causes the behavior to occur. Thus, Darwin’s theory gave rise to functionalism, a belief that characteristics of living organisms perform useful functions. So, to understand the physiological basis of various behaviors, we must first discover what these behaviors accomplish. We must therefore understand something about the natural history of the species being studied so that the behaviors can be seen in context. To understand the workings of a complex piece of machinery, we should know what its functions are. This principle is just as true for a living organism as it is for a mechanical device. However, an important difference exists between machines and organisms: Machines have inventors who had a purpose when they designed them, whereas organisms are the result of a long series of accidents. Thus, strictly speak- ing, we cannot say that any physiological mechanisms of living organisms have a purpose, but they do have functions, and these we can try to determine. For example, the forelimbs shown in Figure 1.8 are adapted for different uses in different species of mammals. (See Figure 1.8.) Inter imSummar y The Nature of Behavioral Neuroscience All scientists hope to explain natural phenomena. In this context, the term explanation has two basic meanings: generalization and reduction. Generalization refers to the classification of phenomena according to their essential features so that general laws can be for- mulated. For example, observing that gravitational attraction is related to the mass of two bodies and to the distance between them helps to explain the movement of planets. Reduction refers to the description of phenomena in terms of more basic physical processes. For example, gravitation can be explained in terms of forces and subatomic particles. Behavioral neuroscientists use both generalization and reduc- tion to explain behavior. In large part, generalizations use the tradi- tional methods of psychology. Reduction explains behaviors in terms of physiological events that occur within the body—primarily within the nervous system. Thus, behavioral neuroscience builds upon the tradition of both experimental psychology and experimental physiology. The behavioral neuroscience of today is rooted in important developments of the past. René Descartes proposed a model of the brain based on hydraulically activated statues. His model stimulated observations that produced important discoveries. The results of Gal- vani’s experiments eventually led to an understanding of the nature of the message transmitted by nerves between the brain and the sen- sory organs and the muscles. Müller’s doctrine of specific nerve ener- gies paved the way for study of the functions of specific parts of the brain through the methods of experimental ablation and electrical stimulation. Thought Questions 1. What is the value of studying the history of behavioral neuro- science? Is it a waste of time? 2. Suppose we studied just the latest research and ignored expla- nations that we now know to be incorrect. Would we be spend- ing our time more profitably, or might we miss something? North Wind Picture Archives. FIGURE 1.7 Charles Darwin (1809–1882). Darwin’s theory of evolution revolutionized biology and strongly influenced early psychologists. ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 10 A good example of the functional analysis of an adaptive trait was demonstrated in an experiment by Blest (1957). Certain species of moths and butterflies have spots on their wings that resemble eyes—particularly the eyes of predators such as owls. (See Figure 1.9.) These insects normally rely on camouflage for protection; the backs of their wings, when folded, are colored like the bark of a tree. However, when a bird approaches, the insect’s wings flip open, and the hidden eyespots are sud- denly displayed. The bird then tends to fly away, rather than eat the insect. Blest per- formed an experiment to see whether the eyespots on a moth’s or butterfly’s wings really disturbed birds that saw them. He placed mealworms on different back- grounds and counted how many worms the birds ate. Indeed, when the worms were placed on a background that contained eyespots, the birds tended to avoid them. Darwin formulated his theory of evolution to explain the means by which species acquired their adaptive characteristics. The cornerstone of this theory is the principle of natural selection. Darwin noted that members of a species were not all identical and that some of the differences they exhibited were inherited by their offspring. If an individual’s characteristics permit it to reproduce more suc- cessfully, some of the individual’s offspring will inherit the favorable characteris- tics and will themselves produce more offspring. As a result, the characteristics will become more prevalent in that species. He observed that animal breeders were able to develop strains that possessed particular traits by mating together only ani- mals that possessed the desired traits. If artificial selection, controlled by animal breeders, could produce so many varieties of dogs, cats, and livestock, perhaps natural selection could be responsible for the development of species. Of course, it was the natural environment, not the hand of the animal breeder, that shaped the process of evolution. Darwin and his fellow scientists knew nothing about the mechanism by which the principle of natural selection works. In fact, the principles of molecular genet- ics were not discovered until the middle of the twentieth century. Briefly, here is how the process works: Every sexually reproducing multicellular organism consists of a large number of cells, each of which contains chromosomes. Chromosomes are large, complex molecules that contain the recipes for producing the proteins that cells need to grow and to perform their functions. In essence, the chromosomes contain the blueprints for the construction (that is, the embryological develop- ment) of a particular member of a particular species. If the plans are altered, a dif- ferent organism is produced. The plans do get altered; mutations occur from time to time. Mutations that affect the development of offspring are accidental changes in the chromosomes of natural selection The process by which inherited traits that confer a selective advantage (increase an ani- mal’s likelihood to live and repro- duce) become more prevalent in the population. mutation A change in the genetic information contained in the chromosomes of sperms or eggs, which can be passed on to an organ- ism’s offspring; provides genetic vari- ability. (a) (b) (c) (d) FIGURE 1.8 Bones of the Forelimb. The figure shows the bones of (a) human, (b) bat, (c) whale, and (d) dog. Through the process of natural selection, these bones have been adapted to suit many different functions. FIGURE 1.9 The Owl Butterfly. This butterfly displays its eyespots when approached by a bird. The bird usually will fly away. Natural Selection and Evolution 11 ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 11 selective advantage A characteristic of an organism that permits it to produce more than the average number of offspring of its species. evolution A gradual change in the structure and physiology of plant and animal species—generally pro- ducing more complex organisms—as a result of natural selection. 12 CHAPTER 1: Origins of Behavioral Neuroscience sperms or eggs that join together and develop into new organisms. For example, cos- mic radiation might strike a chromosome in a cell of an animal’s testis or ovary, thus producing a mutation that affects that animal’s offspring. Most mutations are dele- terious; the offspring either fails to survive or survives with some sort of defect. How- ever, a small percentage of mutations are beneficial and confer a selective advantage to the organism that possesses them. That is, the animal is more likely than other members of its species to live long enough to reproduce and hence to pass on its chromosomes to its own offspring. Many different kinds of traits can confer a selec- tive advantage: resistance to a particular disease, the ability to digest new kinds of food, more effective weapons for defense or for procurement of prey, and even a more attractive appearance to members of the other sex (after all, one must repro- duce in order to pass on one’s chromosomes). Naturally, the traits that can be altered by mutations are physical ones; chromo- somes make proteins, which affect the structure and chemistry of cells. But the effects of these physical alterations can be seen in an animal’s behavior. Thus, the process of natural selection can act on behavior indirectly. For example, if a partic- ular mutation results in changes in the brain that cause a small animal to stop mov- ing and freeze when it perceives a novel stimulus, that animal is more likely to escape undetected when a predator passes nearby. This tendency makes the animal more likely to survive and produce offspring, thus passing on its genes to future generations. Other mutations are not immediately favorable, but because they do not put their possessors at a disadvantage, they are inherited by at least some members of the species. As a result of thousands of such mutations, the members of a particular species possess a variety of genes and are all at least somewhat different from one another. Variety is a definite advantage for a species. Different environments provide optimal habitats for different kinds of organisms. When the environment changes, species must adapt or run the risk of becoming extinct. If some members of the species possess assortments of genes that provide characteristics that permit them to adapt to the new environment, their offspring will survive, and the species will continue. Evolution of the Human Species To evolve means to develop gradually (from the Latin evolvere, “to unroll”). The pro- cess of evolution is a gradual change in the structure and physiology of plant and ani- mal species as a result of natural selection. New species evolve when organisms develop novel characteristics that can take advantage of unexploited opportunities in the environment. The first vertebrates to emerge from the sea—some 360 million years ago— were amphibians. In fact, amphibians have not entirely left the sea; they still lay their eggs in water, and the larvae that hatch from them have gills and only later transform into adults with air-breathing lungs. Seventy million years later, the first reptiles appeared. Reptiles had a considerable advantage over amphibians: Their eggs, enclosed in a shell just porous enough to permit the developing embryo to breathe, could be laid on land. Thus, reptiles could inhabit regions away from bod- ies of water, and they could bury their eggs where predators would be less likely to find them. Reptiles soon divided into three lines: the anapsids, the ancestors of today’s turtles; the diapsids, the ancestors of dinosaurs, birds, lizards, crocodiles, and snakes; and the synapsids, the ancestors of today’s mammals. One group of synapsids, the therapsids, became the dominant land animal during the Permian period. Then, about 248 million years ago, the end of the Permian period was marked by a mass extinction. Dust from a catastrophic series of volcanic eruptions in present-day Siberia darkened the sky, cooled the earth, and wiped out approximately 95 percent of all animal species. Among those that survived was a small therapsid known as a ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 12 Natural Selection and Evolution 15 that established their status as the dominant species. All of these characteristics required a larger brain. A large brain requires a large skull, and an upright posture limits the size of a woman’s birth canal. A newborn baby’s head is about as large as it can be. As it is, the birth of a baby is much more arduous than the birth of mammals with propor- tionally smaller heads, including those of our closest primate relatives. Because a baby’s brain is not large or complex enough to perform the physical and intellectual abilities of an adult, it must continue to grow after the baby is born. In fact, all mam- mals (and all birds, for that matter) require parental care for a period of time while the nervous system develops. The fact that young mammals (and, particularly, young humans) are guaranteed to be exposed to the adults who care for them means that a period of apprenticeship is possible. Consequently, the evolutionary process did not have to produce a brain that consisted solely of specialized circuits of nerve cells that performed specialized tasks. Instead, it could simply produce a larger brain with an abundance of neural circuits that could be modified by experi- ence. Adults would nourish and protect their offspring and provide them with the skills they would need as adults. Some specialized circuits were necessary, of course (for example, those involved in analyzing the complex sounds we use for speech), but by and large, the brain is a general-purpose, programmable computer. What types of genetic changes are required to produce a larger brain? This question will be addressed in greater detail in Chapter 3, but the most important principle appears to be a slowing of the process of maturation, allowing more time for growth. As we will see, the prenatal period of cell division in the brain is pro- longed in humans, which results in a brain weighing an average of 350 g and con- taining approximately 100 billion neurons. After birth, the brain continues to grow. Production of new neurons almost ceases, but those that are already present grow and establish connections with each other, and other types of brain cells, which pro- tect and support neurons, begin to proliferate. Not until late adolescence does the human brain reaches its adult size of approximately 1400 g—about four times the weight of a newborn’s brain. This prolongation of maturation is known as neoteny (roughly translated as “extended youth”). The mature human head and brain retain some infantile characteristics, including their disproportionate size relative to the rest of the body. Figure 1.12 shows fetal and adult skulls of chimpanzees and humans. As you can see, the fetal skulls are much more similar than those of the adults. The grid lines show the pattern of growth, indicating much less change in the human skull from birth to adulthood. (See Figure 1.12.) neoteny A slowing of the process of maturation, allowing more time for growth; an important factor in the development of large brains. Redrawn from Lewin, R. Human Evolution: An Illustrated Introduction, 3rd ed. Boston: Blackwell Scientific Publications, 1993. Reprinted with permission by Blackwell Science Ltd. Human fetusChimp adultChimp fetus Human adult FIGURE 1.12 Neoteny in Evolution of the Human Skull. The skulls of fetal humans and chimpanzees are much more similar than are those of the adults. The grid lines show the pattern of growth, indicating much less change in the human skull from birth to adulthood. ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 15 Ethical Issues in Research with Animals Most of the research described in this book involves experimentation on living ani- mals. Any time we use another species of animals for our own purposes, we should be sure that what we are doing is both humane and worthwhile. I believe that a good case can be made that research on the physiology of behavior qualifies on both counts. Humane treatment is a matter of procedure. We know how to maintain lab- oratory animals in good health in comfortable, sanitary conditions. We know how to administer anesthetics and analgesics so that animals do not suffer during or after surgery, and we know how to prevent infections with proper surgical proce- dures and the use of antibiotics. Most industrially developed societies have very strict regulations about the care of animals and require approval of the experimen- tal procedures used on them. There is no excuse for mistreating animals in our care. In fact, the vast majority of laboratory animals are treated humanely. We use animals for many purposes. We eat their meat and eggs, and we drink their milk; we turn their hides into leather; we extract insulin and other hormones Inter imSummar y Natural Selection and Evolution Darwin’s theory of evolution, which was based on the concept of nat- ural selection, provided an important contribution to modern behav- ioral neuroscience. The theory asserts that we must understand the functions performed by an organ or body part or by a behavior. Through random mutations, changes in an individual’s genetic mate- rial cause different proteins to be produced, which results in the alteration of some physical characteristics. If the changes confer a selective advantage on the individual, the new genes will be trans- mitted to more and more members of the species. Even behaviors can evolve through the selective advantage of alterations in the structure of the nervous system. Amphibians emerged from the sea 360 million years ago. One branch, the therapsids, became the dominant land animal until a catastrophic series of volcanic eruptions wiped out most animal species. A small therapsid, the cynodont, survived the disaster and became the ancestor of the mammals. The earliest mammals were small, nocturnal insectivores who lived in trees. They remained small and inconspicuous until the extinction of the dinosaurs, which occurred around 65 million years ago. The vacant ecological niches were quickly filled by mammals. Primates also began as small, noc- turnal, tree-dwelling insectivores. Larger fruit-eating primates, with forward-facing eyes and larger brains, eventually evolved. The first hominids appeared in Africa around 25 million years ago, eventually evolving into four major species: orangutans, gorillas, chimpanzees, and humans. Our ancestors acquired bipedalism around 3.7 million years ago and discovered toolmaking around 2.5 million years ago. The first hominids to leave Africa, Homo erectus, did so around 1.7 million years ago and scattered across Europe and Asia. Homo neanderthalis evolved in Western Europe, eventually to be replaced by Homo sapiens, which evolved in Africa around 100,000 years ago and spread throughout the world. By 30,000 years ago, Homo sapiens had replaced Homo neanderthalis. The evolution of large brains made possible the development of toolmaking, fire building, and language, which in turn permitted the development of complex social structures. Large brains also pro- vided a large memory capacity and the abilities to recognize pat- terns of events in the past and to plan for the future. Because an upright posture limits the size of a woman’s birth canal and therefore the size of the head that passes through it, much of the brain’s growth must take place after birth, which means that children require an extended period of parental care. This period of apprenticeship enabled the developing brain to be modified by experience. Although human DNA differs from that of chimpanzees by only 1.2 percent, our brains are more than three times larger, which means that a small number of genes is responsible for the increase in the size of our brains. These genes appear to retard the events that stop brain development, resulting in a phenomenon known as neoteny. Thought Questions 1. What useful functions are provided by the fact that a human can be self-aware? How was this trait selected for during the evolution of our species? 2. Are you surprised that the difference in the DNA of humans and chimpanzees is only 1.2 percent? How do you feel about this fact? 3. If our species continues to evolve, what kinds of changes do you think might occur? 16 CHAPTER 1: Origins of Behavioral Neuroscience ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 16 Ethical Issues in Research with Animals 17 from their organs to treat people’s diseases; we train them to do useful work on farms or to entertain us. Even having a pet is a form of exploitation; it is we—not they—who decide that they will live in our homes. The fact is, we have been using other ani- mals throughout the history of our species. Pet owning causes much more suffering among animals than scientific research does. As Miller (1983) notes, pet own- ers are not required to receive permission from a board of experts that includes a veterinarian to house their pets, nor are they subject to periodic inspections to be sure that their homes are clean and sanitary, that their pets have enough space to exercise properly, or that their pets’ diets are appropriate. Sci- entific researchers are. Miller also notes that fifty times more dogs and cats are killed by humane societies each year because they have been abandoned by former pet owners than are used in scientific research. If a person believes that it is wrong to use another animal in any way, regardless of the benefits to humans, there is noth- ing anyone can say to convince him or her of the value of sci- entific research with animals. For this person the issue is closed from the very beginning. Moral absolutes cannot be settled logically; like religious beliefs, they can be accepted or rejected, but they cannot be proved or disproved. My argu- ments in support of scientific research with animals are based on an evaluation of the benefits the research has to humans. (We should also remember that research with animals often helps other animals; procedures used by veterinarians, as well as those used by physicians, come from such research.) Before describing the advantages of research with animals, let me point out that the use of animals in research and teaching is a special target of animal rights activists. Nicholl and Russell (1990) examined twenty-one books written by such activists and counted the number of pages devoted to concern for different uses of animals. Next, they compared the relative concern the authors showed for these uses to the numbers of animals actually involved in each of these categories. The results indicate that the authors showed relatively little concern for animals used for food, hunting, or furs, or for those killed in pounds. In contrast, although only 0.3 percent of the animals are used for research and education, 63.3 percent of the pages were devoted to criticizing this use. In terms of pages per million ani- mals used, the authors devoted 0.08 to food, 0.23 to hunting, 1.27 to furs, 1.44 to killing in pounds—and 53.2 to research and education. The authors showed 665 times more concern for research and education than for food and 231 times more than for hunting. Even the use of animals for furs (which consumes two-thirds as many animals as research and education) attracted 41.9 times less attention per animal. The disproportionate amount of concern that animal rights activists show toward the use of animals in research and education is puzzling, particularly because this is the one indispensable use of animals. We can survive without eating animals, we can live without hunting, we can do without furs. But without using animals for research and for training future researchers, we cannot make progress in understanding and treating diseases. In not too many years, scientists probably will develop a vaccine that will prevent the further spread of AIDS. Some animal rights activists believe that preventing the deaths of laboratory animals in the pursuit of such a vaccine is a more worthy goal than preventing the deaths of mil- lions of humans that will occur as a result of the disease if a vaccine is not found. Even diseases that we have already conquered would take new victims if drug companies could no longer use animals. If they were deprived of animals, these Unlike pet owners, scientists who use animals in their research must follow stringent regulations designed to ensure that the animals are properly cared for. ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 17 Strategies for Learning The brain is a complicated organ. After all, it is responsible for all our abilities and all our complexities. Scientists have been studying this organ for a good many years and (especially in recent years) have been learning a lot about how it works. It is impossible to summarize this progress in a few simple sentences; therefore, this book contains a lot of information. I have tried to organize this information logically, telling you what you need to know in the order you need to know it. (After all, to understand some things, you need to understand other things first.) I have also tried to write as clearly as possible, making my examples as simple and as vivid as I can. Still, you cannot expect to master the information in this book by simply giving it a passive read; you will have to do some work. Learning about the physiology of behavior involves much more than memoriz- ing facts. Of course, there are facts to be memorized: names of parts of the nervous system, names of chemicals and drugs, scientific terms for particular phenomena and procedures used to investigate them, and so on. Still, the quest for information is nowhere near completed; we know only a small fraction of what we have to learn— and almost certainly, many of the “facts” that we now accept will someday be shown to be incorrect. If all you do is learn facts, where will you be when these facts are revised? The antidote to obsolescence is knowledge of the process by which facts are obtained. In science, facts are the conclusions scientists make about their observa- tions. If you learn only the conclusions, obsolescence is almost guaranteed. You will have to remember which conclusions are overturned and what the new conclusions are, and that kind of rote learning is hard to do. However, if you learn about the research strategies the scientists use, the observations they make, and the reasoning that leads to the conclusions, you will develop an understanding that is easily revised when new observations are made and new “facts” emerge. If you understand what lies behind the conclusions, then you can incorporate new information into what you already know and revise these conclusions yourself. In recognition of these realities about learning, knowledge, and the scientific method, this book presents not just a collection of facts, but also a description of the procedures, experiments, and logical reasoning that scientists have used in their attempt to understand the physiology of behavior. If, in the interest of expediency, you focus on the conclusions and ignore the process that leads to them, you run the risk of acquiring information that will quickly become obsolete. On the other hand, if you try to understand the experiments and see how the conclusions follow from the results, you will acquire knowledge that lives and grows. 20 CHAPTER 1: Origins of Behavioral Neuroscience Inter imSummar y Ethical Issues in Research with Animals and Careers in Neuroscience Research on the physiology of behavior necessarily involves the use of laboratory animals. It is incumbent on all scientists using these ani- mals to see that they are housed comfortably and treated humanely, and laws have been enacted to ensure that they are. Such research has already produced many benefits to humankind and promises to continue to do so. Behavioral neuroscience (originally called physiological psy- chology and also called biological psychology, biopsychology, and psychobiology) is a field devoted to our understanding of the phys- iology of behavior. Behavioral neuroscientists are allied with other scientists in the broader field of neuroscience. To pursue a career in behavioral neuroscience (or in the sister field of experimental neuropsychology), one must obtain a graduate degree and (usually) serve 2 years or more as a “postdoc”—a scientist pursuing further training. Thought Question Why do you think some people are apparently more upset about using animals for research and teaching than about using them for other purposes? ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 20 Strategies for Learning 21 Now let me offer some practical advice about studying. You have been studying throughout your academic career, and you have undoubtedly learned some useful strategies along the way. Even if you have developed efficient and effective study skills, at least consider the possibility that there might be some ways to improve them. If possible, the first reading of the assignment should be as uninterrupted as you can make it; that is, read the chapter without worrying much about remembering details. Next, after the first class meeting devoted to the topic, read the assignment again in earnest. Use a pen or pencil as you go, making notes. Don’t use a highlighter. Sweeping the felt tip of a highlighter across some words on a page provides some instant gratification; you can even imagine that the highlighted words are somehow being transferred to your knowledge base. You have selected what is important, and when you review the reading assignment you have only to read the highlighted words. But this is an illusion. Be active, not passive. Force yourself to write down whole words and phrases. The act of putting the information into your own words will not only give you something to study shortly before the next exam but also put something into your head (which is helpful at exam time). Using a highlighter puts off the learning until a later date; rephrasing the information in your own words starts the learning process right then. A good way to get yourself to put the information into your own words (and thus into your own brain) is to answer the questions in the study guide. If you can- not answer a question, look up the answer in the book, close the book, and write the answer down. The phrase close the book is important. If you copy the answer, you will get very little out of the exercise. However, if you make yourself remember the infor- mation long enough to write it down, you have a good chance of remembering it later. The importance of the study guide is not to have a set of short answers in your own handwriting that you can study before the quiz. The behaviors that lead to long- term learning are doing enough thinking about the material to summarize it in your own words, then going through the mechanics of writing those words down. Before you begin reading the next chapter, let me say a few things about the design of the book that might help you with your studies. The text and illustrations are integrated as closely as possible. In my experience, one of the most annoying aspects of reading some books is not knowing when to look at an illustration. There- fore, in this book you will find figure references in boldfaced italics (like this: Figure 5.6), which means “stop reading and look at the figure.” These references appear in locations I think will be optimal. If you look away from the text then, you will be assured that you will not be interrupting a line of reasoning in a crucial place and will not have to reread several sentences to get going again. You will find sections like this: “Figure 4.1 shows an alligator and a human. This alligator is certainly laid out in a linear fashion; we can draw a straight line that starts between its eyes and con- tinues down the center of its spinal cord. (See Figure 4.1.)” This particular example is a trivial one and will give you no problems no matter when you look at the figure, but in other cases the material is more complex, and you will have less trouble if you know what to look for before you stop reading and examine the illustration. You will notice that some words in the text are italicized and others are printed in boldface. Italics mean one of two things: Either the word is being stressed for emphasis and is not a new term, or I am pointing out a new term that is not neces- sary for you to learn. On the other hand, a word in boldface is a new term that you should try to learn. Most of the boldfaced terms in the text are part of the vocabu- lary of behavioral neuroscience. Often, they will be used again in a later chapter. As an aid to your studying, definitions of these terms are printed in the margin of the page, along with pronunciation guides for those terms whose pronunciation is not obvious. In addition, a comprehensive index at the end of the book provides a list of terms and topics, with page references. At the end of each major section (there are usually three to five of them in a chapter) you will find an Interim Summary, which provides a place for you to stop and think again about what you have just read to make sure that you understand the ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 21 22 CHAPTER 1: Origins of Behavioral Neuroscience direction in which the discussion has gone. Many interim summaries are followed by some thought questions, which may serve to stimulate your thoughts about what you have learned and apply them to questions that have not yet been answered. Taken together, these sections provide a detailed summary of the information intro- duced in the chapter. My students tell me that they review the interim summaries just before taking a test. Okay, the preliminaries are over. The next chapter starts with something you can sink your (metaphorical) teeth into: the structure and functions of neurons, the most important elements of the nervous system. René Descartes had no way to study the operations of the nervous system. He did, however, understand how the statues in the Royal Gardens at Saint- Germain were powered and controlled, which led him to view the body as a complicated piece of plumbing. Many scientists have followed Descartes’s example, using technological devices that were fashionable at the time to explain how the brain worked. What motivates people to use artificial devices to explain the workings of the brain? The most important reason, I suppose, is that the brain is enormously complicated. Even the most complex human inventions are many times simpler than the brain, and because they have been designed and made by people, people can understand them. If an artificial device can do some of the things that the brain does, then perhaps both the brain and the device accomplish their tasks in the same way. Most models of brain function developed in the last half of the twentieth century have been based on the modern, general- purpose digital computer. Actually, they have been based not on the computers themselves but on computer programs. Computers can be programmed to store any kind of information that can be coded in numbers or words, can solve any logical problem that can be explicitly described, and can compute any mathematical equations that can be written. Therefore, in principle at least, they can be programmed to do the things we do: perceive, remember, make deductions, solve problems. The construction of computer programs that simulate human brain functions can help to clarify the nature of these functions. For instance, to construct a program and simulate, say, percep- tion and classification of certain types of patterns, the investiga- tor is forced to specify precisely what is required by the task of pattern perception. If the program fails to recognize the patterns, then the investigator knows that something is wrong with the model or with the way it has been implemented in the program. The investigator revises the model, tries again, and keeps working until it finally works (or until he or she gives up the task as being too ambitious). EPILOGUE Models of Brain Functions Ideally, this task tells the investigator the kinds of processes the brain must perform. However, there is usually more than one way to accomplish a particular goal; critics of computer modeling have pointed out that it is possible to write a program that performs a task that the human brain performs and comes up with exactly the same results but does the task in an entirely different way. In fact, some say, given the way that computers work and what we know about the structure of the human brain, the computer pro- gram is guaranteed to work differently. When we base a model of brain functions on a physical device with which we are familiar, we enjoy the advantage of being able to think concretely about something that is difficult to observe. However, if the brain does not work like a computer, then our models will not tell us very much about the brain. Such models are constrained (“restricted”) by the computer metaphor; they will be able to do things only the way that computers can do them. If the brain can actually do some different sorts of things that com- puters cannot do, the models will never contain these features. In fact, computers and brains are fundamentally different. Modern computers are serial devices; they work one step at a time. (Serial, from the Latin sererei “to join,” refers to events that occur in order, one after the other.) Programs consist of a set of instruc- tions stored in the computer’s memory. The computer follows these instructions, one at a time. Because each of these steps takes time, a complicated program will take more time to execute. But we do some things extremely quickly that computers take a very long time to do. The best example is visual perception. We can rec- ognize a complex figure about as quickly as a simple one; for example, it takes about the same amount of time to recognize a friend’s face as it does to identify a simple triangle. The same is not true at all for a serial computer. A computer must “examine” the scene through an input device something like a video camera. Information about the brightness of each point of the picture must be converted into a number and stored in a memory loca- tion. Then the program examines each memory location, one at a time, and does calculations that determine the locations of ALBQ155_ch1.qxp 10/26/09 10:15 AM Page 22