Unit 1 - Bibliography PDF

1 The Development of Neuropsychology Living with Traumatic Brain Injury aware that he was in a hospital 3 weeks later. L.D. was unable to return to work because he found the multitasking involved in preparing meals too difficult. He was seeking compensation from the company that had hosted the spor...

1 The Development of Neuropsychology Living with Traumatic Brain Injury aware that he was in a hospital 3 weeks later. L.D. was unable to return to work because he found the multitasking involved in preparing meals too difficult. He was seeking compensation from the company that had hosted the sports promotion and from the pub where he had been injured. We found that L.D. became frustrated and annoyed when attempting to cook. He had lost his sense of smell and taste and was not interested in socializing. He and his girlfriend had ended their 4-year relationship. We administered a comprehensive neuropsychological examination, and his scores on most tests were typical, except for tests of verbal memory and attention. Magnetic resonance imaging (MRI), a brain-scanning method that can reveal the brain’s structure in detail, showed some diffuse damage to both sides of his brain. The accompanying positron emission tomography (PET) images contrast blood flow in a healthy brain (top) to blood flow in patients like L.D. (bottom). Based on previous patients with traumatic brain injuries and behavioral and brain symptoms similar to L.D.’s, we recommended compensation, which L.D. did receive, in addition to assistance in finding work less demanding than cooking. He was able to live on his own and successfully returned to playing golf. COURTESY DR. MARVIN BERGSNEIDER L.D., an aspiring golfer, had worked as a cook. Following brain damage, the lawyers negotiating his case puzzled over how L.D. continued to excel at golf but at the same time was unable to return to his former work as a cook. Four years earlier, when he was 21, L.D. had been invited to participate in a sports promotion at a pub. He became ill and was helped onto a balcony by a pub employee. On the balcony, he slipped out of the employee’s grasp and fell down five flights of stairs, striking his head against the stairs and wall. He was taken, unconscious, to the emergency ward of the local hospital, where his concussion was assessed on the Glasgow Coma Scale rating as 3, the lowest score on a scale from 3 to 15. A computed tomography (CT) scan revealed bleeding and swelling on the right side of L.D.’s brain. A neurosurgeon performed a craniotomy (skull removal) over his right frontal cortex to relieve pressure and remove blood. A subsequent CT scan revealed further bleeding on the left side of his brain, and a second craniotomy was performed. When discharged from the hospital 6 weeks later, L.D.’s recall of the events consisted only of remembering that he had entered the pub and then becoming COURTESY DR. MARVIN BERGSNEIDER PORTRAIT According to National Institute of Neurological Disorders and Stroke estimates, 1.7 million U.S. residents receive medical attention each year after suffering traumatic brain injury (TBI), a wound to the brain that results from a blow to the head (detailed in Section 26.3, including concussion, the common term for mild TBI). TBI is a contributing factor in 30% of deaths due to accidents and can result from head blows while playing sports, from falls, and from vehicle accidents. While also the most common cause of discharge from military service 1 2 PART I B ACK GRO UN D (Gubata et al., 2013), TBI most frequently occurs in children under the age of 6, young adults, and those over age 65. The number of people who endure TBI each year but do not report an injury is not known. L.D. is not unusual in that, in his own view and in the view of acquaintances, he has mainly recovered, but lingering problems prevent him from resuming his former level of employment. L.D. is also not unusual in that he puzzles both friends and experts with his ability to do some things well while being unable to do other things that appear less difficult. Finally, L.D. is not unusual in that the diffuse brain injury revealed by brain-scanning methods (see Chapter 7) does not predict his abilities and disabilities well. Neuropsychological testing is required to confirm that he has enduring cognitive deficits and to identify those deficits. L.D.’s poor scores on tests of memory and attention are associated with his difficulty in everyday problem solving, a mental skill referred to as executive function. Thus, L.D. can play golf at a high level because it requires that he execute only one act at a time, but he cannot prepare a meal, which requires him to multitask. This book’s objective is to describe neuropsychology, the scientific study of the relations between brain function and behavior. Neuropsychology draws information from many disciplines—anatomy, biology, biophysics, ethology, pharmacology, physiology, physiological psychology, and philosophy among them. Neuropsychological investigations into the brain–behavior relationship can identify impairments in behavior that result from brain trauma and from diseases that affect the brain. Neuropsychology is strongly influenced by two experimental and theoretical investigations into brain function: the brain theory, which states that the brain is the source of behavior; and the neuron theory, the idea that the unit of brain structure and function is the neuron, or nerve cell. This chapter traces the development of these two theories and introduces neuropsychology’s major principles, which have emerged from investigating brain function and which we apply in subsequent chapters. 1.1 The Brain Theory People knew what the brain looked like long before they had any idea of what it did. Early in human history, hunters must have noticed that all animals have brains and that the brains of different animals, including humans, although varying greatly in size, look quite similar. Over the past 2000 years, anatomists have produced drawings of the brain, named its distinctive parts, and developed methods to describe the functions of those parts. What Is the Brain? Brain is an Old English word for the tissue found within the skull (cranium). Figure 1.1A shows a human brain as oriented in the skull of an upright human. Just as your body is symmetrical, having two arms and two legs, so is your brain. Its two almost symmetrical halves are called hemispheres, one on the left side of the body and the other on the right, as shown in the frontal view. If you make your right hand into a fist and hold it up with the thumb pointing toward the front, the fist can represent the brain’s left hemisphere as positioned within the skull (Figure 1.1B). CHAPTER 1 THE DEVELOPMENT OF NEUROPSYCHOLOGY §1.1 (A) (B) Frontal view The brain is made up of two hemispheres, left and right. Frontal lobe Temporal lobe Your right hand, if made into a fist, represents the positions of the lobes of the left hemisphere of your brain. The cerebral cortex is the brain’s thin outer “bark” layer. Longitudinal fissure Corpus callosum Parietal lobe Occipital lobe 3 Frontal lobe (fingers) Parietal lobe (knuckles) Occipital lobe (wrist) Lateral fissure Lobes define broad divisions of the cerebral cortex. Bumps in the brain's folded surface are called gyri, and cracks are called sulci. Temporal lobe (thumb) Brainstem Cerebellum Figure 1.1 ! The Human Brain (A) The The brain’s basic plan is that of a tube filled with salty fluid called cerebrospinal fluid (CSF), which cushions the brain and assists in removing metabolic waste. Parts of the tube’s covering have bulged outward and folded, forming the more complicated-looking surface structures that initially catch the eye in Figure 1.1A. The brain’s most conspicuous outer feature is the crinkled tissue that has expanded from the front of the tube to such an extent that it folds over and covers much of the rest of the brain (Figure 1.1A at right). This outer layer is the cerebral cortex (usually referred to as just the cortex). The word cortex, meaning “bark” in Latin, is apt, because the cortex’s folded appearance resembles the bark of a tree and because, as bark covers a tree, cortical tissue covers most of the rest of the brain. The folds, or bumps, in the cortex are called gyri (gyrus is Greek for “circle”), and the creases between them are called sulci (sulcus is Greek for “trench”). Some large sulci are called fissures: the longitudinal fissure, shown in the Figure 1.1 frontal view, divides the two hemispheres, and the lateral fissure divides each hemisphere into halves. (In our fist analogy, the lateral fissure is the crease separating the thumb from the other fingers.) Pathways called commissures, the largest of which is the corpus callosum, connect the brain’s hemispheres. The cortex of each hemisphere forms four lobes, each named after the skull bones beneath which they lie. The temporal lobe is located below the lateral fissure at approximately the same place as the thumb on your upraised fist (Figure 1.1B). Lying immediately above the temporal lobe is the frontal lobe, so called because it is located at the front of the brain beneath the frontal bones. The parietal lobe is located behind the frontal lobe, and the occipital lobe constitutes the area at the back of each hemisphere. The cerebral cortex constitutes most of the forebrain, so named because it develops from the front part of the neural tube that makes up an embryo’s primitive brain. The remaining “tube” underlying the cortex is the brainstem. The brainstem is in turn connected to the spinal cord, which descends down the back within the vertebral column. To visualize the relations among these parts of the brain, again imagine your upraised fist: the folded fingers represent the cortex, the heel of the hand represents the brainstem, and the arm represents the spinal cord. human brain, as oriented in the head. The visible part of the intact brain is the cerebral cortex, a thin sheet of tissue folded many times and fitting snugly inside the skull. (B) Your right fist can serve as a guide to the orientation of the brain and its cerebral lobes. (Photograph: Arthur Glauberman/ Science Source.) 4 PART I B ACK GRO UN D This three-part brain is conceptually useful evolutionarily, anatomically, and functionally. Evolutionarily, animals with only spinal cords preceded those with brainstems, which preceded those with forebrains. Anatomically, in prenatal development, the spinal cord forms before the brainstem, which forms before the forebrain. Functionally, the forebrain mediates cognitive functions; the brainstem mediates regulatory functions such as eating, drinking, and moving; and the spinal cord conveys sensory information into the brain and sends commands from the brain to the muscles to move. How Does the Brain Relate to the Rest of the Nervous System? The brains and spinal cords of mammals are encased in protective bones: the skull protects the brain, and vertebrae protect the spinal cord. Together, the brain and spinal cord are called the central nervous system, or CNS. The CNS is connected to the rest of the body through nerve fibers. Some fibers carry information away from the CNS; others bring information into it. These nerve fibers constitute the peripheral nervous system, or PNS. One distinguishing feature between the central and peripheral nervous systems is that PNS tissue will regrow after damage, whereas the CNS does not regenerate lost tissue. Thus the long-term prospect for L.D. is that he will show little further recovery in higher brain functions such as planning, but his golf game may improve. Figure 1.2 " Nerve fibers that bring information to the CNS are extensively connected Major Divisions of the to sensory receptors on the body’s surface and to muscles, enabling the brain to Human Nervous System sense the world and to react. This subdivision of the PNS is called the somatic The brain and spinal cord together make up the CNS. All the nerve nervous system (SNS). Organized into sensory pathways, collections of fibers processes radiating from it and carry messages for specific senses, such as hearing, vision, and touch. Sensory the neurons outside it connect to pathways carry information collected on one side of the body mainly to the cortex the sensory receptors and muscles in the opposite hemisphere. The brain uses this information to construct percepin the SNS and to internal organs in the ANS. This constitutes the tions of the world, memories of past events, and expectations about the future. peripheral nervous system (PNS). Motor pathways are groups of nerve fibers that connect the brain and spinal cord to the body’s musCentral nervous system (CNS) cles through the SNS. Movements produced by motor The brain is encased by the skull; the spinal pathways include the eye movements that you are using cord is encased by the vertebrae. to read this book, the hand movements that you make Peripheral nervous system (PNS) while turning or scrolling through the pages, and your Neurons and nerve processes outside CNS body’s posture as you read. The parts of the cortex that Somatic nervous system (SNS) produce movement mainly send information out via Sensory connections motor pathways to muscles on the opposite side of the to receptors in the body. Thus, one hemisphere uses muscles on the opskin posite side of the body to produce movement. Sensory and motor pathways also influence the Motor connections muscles of your internal organs—the beating of your to body muscles heart, contractions of your stomach, raising and lowAutonomic nervous system (ANS) ering of your diaphragm to inflate and deflate your Sensory and motor lungs. The pathways that control these organs are a connections to internal subdivision of the PNS called the autonomic nervous body organs system (ANS). Figure 1.2 diagrams these major divisions of the human nervous system. CHAPTER 1 THE DEVELOPMENT OF NEUROPSYCHOLOGY §1.2 5 1.2 Perspectives on the Brain and Behavior The central topic in neuropsychology is how brain and behavior are related. We begin with three classic theories—mentalism, dualism, and materialism— representative of the many attempts scientists and philosophers have made to relate brain and behavior. Then we explain why contemporary brain investigators subscribe to the materialist view. In reviewing these theories, you will recognize that some “commonsense” ideas you might have about behavior are derived from one or another of these perspectives (Finger, 1994). Aristotle: Mentalism The Greek philosopher Aristotle (384–322 B.C.E.) was the first person to develop a formal theory of behavior. He proposed that a nonmaterial psyche is responsible for human thoughts, perceptions, and emotions and for such processes as imagination, opinion, desire, pleasure, pain, memory, and reason. The psyche is independent of the body but in Aristotle’s view, works through the heart to produce action. As in Aristotle’s time, heart metaphors serve to this day to describe our behavior: “put your heart into it” and “she wore her heart on her sleeve” are but two. Aristotle’s view that this nonmaterial psyche governs behavior was adopted by Christianity in its concept of the soul and has been widely disseminated throughout the world. Mind is an Anglo-Saxon word for memory, and, when “psyche” was translated into English, it became mind. The philosophical position that a person’s mind is responsible for behavior is called mentalism, meaning “of the mind.” Mentalism still influences modern neuropsychology: many terms—sensation, perception, attention, imagination, emotion, memory, and volition among them—are still employed as labels for patterns of behavior. (Scan some of the chapter titles in this book.) Mentalism also influences people’s ideas about how the brain might work, because the mind was proposed to be nonmaterial and so have no “working parts.” We still use the term mind to describe our perceptions of ourselves as having unitary consciousness despite recognizing that the brain is composed of many parts, and as we describe in Section 1.3, has many separate functions. Descartes: Dualism René Descartes (1596–1650), a French anatomist and philosopher, wrote what could be considered the first neuropsychology text in 1684. In it he gave the brain a prominent role. Descartes was impressed by machines made in his time, such as those encased in certain statues on display for public amusement in the water gardens of Paris. When a passerby stopped in front of one particular statue, for example, his or her weight depressed a lever under the sidewalk, causing the statue to move and spray water at the person’s face. Descartes proposed that the body is like these machines. It is material and thus clearly has spatial extent, and it responds mechanically and reflexively to events that impinge on it (Figure 1.3). Described as nonmaterial and without spatial extent, the mind, as Descartes saw it, was different from the body. The body Figure 1.3 " Descartes’s Concept of Reflex Action In this mecha- nistic depiction, heat from the flame causes a thread in the nerve to be pulled, releasing ventricular fluid through an opened pore. The fluid flows through the nerve, causing not only the foot to withdraw but the eyes and head to turn to look at it, the hands to advance, and the whole body to bend to protect it. Descartes ascribed to reflexes behaviors that today are considered too complex to be reflexive, whereas he did not conceive of behavior described as reflexive today. (From Descartes, 1664. Print Collector/Getty Images.) 6 PART I B ACK GRO UN D Pineal gland Ventricles operated on principles similar to those of a machine, but the mind decided what movements the machine should make. Descartes located the site of action of the mind in the pineal body, a small structure high in the brainstem. His choice was based on the logic that the pineal body is the only structure in the nervous system not composed of two bilaterally symmetrical halves and moreover that it is located close to the ventricles. His idea was that the mind, working through the pineal body, controlled valves that allowed CSF to flow from the ventricles through nerves to muscles, filling them and making them move. For Descartes, the cortex was not functioning neural tissue but merely a covering for the pineal body. People later argued against Descartes’s hypothesis by pointing out that no obvious changes in behavior occur when the pineal body is damaged. Today, the pineal body, now called the pineal gland, is known to influence daily and seasonal biorhythms. And the cortex became central to understanding behavior as scientists began to discover that it performs the functions Descartes attributed to a nonmaterial mind. Descartes’s position that mind and body are separate but can interact is called dualism, to indicate that behavior is caused by two things. Dualism originated a quandary known as the mind–body problem: for Descartes, a person is capable of consciousness and rationality only because of having a mind, but how can a nonmaterial mind produce movements in a material body? To understand the mind–body problem, consider that for the mind to affect the body, it must expend energy, adding new energy to the material world. The spontaneous creation of new energy violates a fundamental law of physics, the law of conservation of matter and energy. Thus, dualists who argue that mind and body interact causally cannot explain how. Other dualists avoid this problem by reasoning either that the mind and body function in parallel, without interacting, or that the body can affect the mind but the mind cannot affect the body. These dualist positions allow for both a body and a mind by sidestepping the problem of violating the laws of physics. Descartes’s theory also spawned unforeseen and unfortunate consequences. In proposing his dualistic theory of brain function, Descartes also proposed that animals do not have minds and therefore are only machinelike, that the mind develops with language in children, and that mental disease impairs rational processes of the mind. Some of his followers justified the inhumane treatment of animals, children, and the mentally ill on the grounds that they did not have minds: an animal did not have a mind, a child developed a mind only at about 7 years of age when able to talk and reason, and the mentally ill had “lost their minds.” Likewise misunderstanding Descartes’s position, some people still argue that the study of animals cannot be a source of useful insight into human neuropsychology. Descartes himself, however, was not so dogmatic. He was kind to his dog, Monsieur Grat. He suggested that whether animals had minds could be tested experimentally. He proposed that the key indications of the presence of a mind are the use of language and reason. He suggested that, if it could be demonstrated that animals could speak or reason, then such demonstration would indicate that they have minds. Exciting lines of research in modern experimental neuropsychology, demonstrated throughout this book, are directed toward the comparative study of animals and humans with respect to language and reason. CHAPTER 1 THE DEVELOPMENT OF NEUROPSYCHOLOGY §1.2 Darwin: Materialism By the mid-nineteenth century, our contemporary perspective of materialism was taking shape. The idea is that rational behavior can be fully explained by the workings of the nervous system. No need to refer to a nonmaterial mind. Materialism has its roots in the evolutionary theories of two English naturalists, Alfred Russel Wallace (1823–1913) and Charles Darwin (1809–1892). Evolution by Natural Selection Darwin and Wallace looked carefully at the structures of plants and animals and at animal behavior. Despite the diversity of living organisms, the two were struck by their many similarities. For example, the skeleton, muscles, internal organs, and nervous systems of humans, monkeys, and other mammals are similar. These observations support the idea that living things must be related, an idea widely held even before Wallace and Darwin. More importantly, these same observations led to the idea that the similarities could be explained if all animals had evolved from a common ancestor. Darwin elaborated his theory in On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life, originally published in 1859. He argued that all organisms, both living and extinct, are descended from an ancestor that lived in the remote past. Animals have similar traits because those traits are passed from parents to their offspring. The nervous system is one such trait, an adaptation that emerged only once in animal evolution. Consequently, the nervous systems of living animals are similar because they are descendants of that first nervous system. Those animals with brains likewise are related, because all animals with brains descend from the first animal to evolve a brain. Natural selection is Darwin’s theory for explaining how new species evolve and how they change over time. A species is a group of organisms that can breed among themselves but usually not with members of other species. Individual organisms within a species vary in their phenotype, the traits we can see or measure. Some are big, some are small, some are fat, some are fast, some are light colored, some have large teeth. Individual organisms whose traits best help them to survive in their environment are likely to leave more offspring that feature those traits. Natural Selection and Heritable Factors Beginning about 1857, Gregor Mendel (1822–1884), an Austrian monk, experimented with plant traits, such as the flower color and height of pea plants, and determined that such traits are due to heritable factors we now call genes (elaborated in Section 2.3). Thus, the unequal ability of individual organisms to survive and reproduce is related to the different genes they inherit from their parents and pass on to their offspring. Mendel realized that the environment plays a role in how genes express traits: planting tall peas in poor soil reduces their height. Likewise, experience affects gene expression: children who lack educational opportunities may not adapt as well in society as children who attend school. The science that studies differences in gene expression related to environment and experience is epigenetics (see Section 2.3). Epigenetic factors do not change the genes individuals inherit, 7 8 PART I B ACK GRO UN D but they do affect whether a gene is active—turned on or off—and in this way influence an individual’s phenotypic traits. Environment and experience play an important role in how animals adapt and learn. Adaptation and learning are in turn enabled by the brain’s ability to form new connections and pathways. This neuroplasticity is the nervous system’s potential for physical or chemical change that enhances its adaptability to environmental change and its ability to compensate for injury. Epigeneticists are especially involved in describing how genes express the brain’s plastic changes under the influence of environment and experience. Contemporary Perspectives As a scientific theory, contemporary brain theory is both materialistic and neutral with respect to beliefs, including religious beliefs. Science is not a belief system but rather a set of procedures designed to allow investigators to confirm answers to questions independently. Behavioral scientists, both those with and those without religious beliefs, use the scientific method to examine relations between the brain and behavior and to replicate (repeat) others’ work on brain– behavior relationships. Today, when neuroscientists use the term mind, most are not referring to a nonmaterial entity but using it as shorthand for the collective functions of the brain. 1.3 Brain Function: Insights from Brain Injury You may have heard statements such as, “Most people use only 10% of their brains” or “He put his entire mind to the problem.” Both statements arise from early suggestions that people with brain damage often get along quite well. Nevertheless, most people who endure brain damage will tell you that some behavior is lost and some survives, as it did for L.D., whose case begins this chapter. Our understanding of brain function has its origins in individuals with brain damage. We now describe some fascinating neuropsychological concepts that have emerged from studying such individuals. Localization of Function The first general theory to propose that different parts of the brain have different functions was developed in the early 1800s by German anatomist Franz Josef Gall (1758–1828) and his partner Johann Casper Spurzheim (1776–1832) (Critchley, 1965). Gall and Spurzheim proposed that the cortex and its gyri were functioning parts of the brain and not just coverings for the pineal body. They supported their position by showing through dissection that the brain’s most distinctive motor pathway, the corticospinal (cortex to spinal cord) tract, leads from the cortex of each hemisphere to the spinal cord on the opposite side of the body. Thus, they suggested, the cortex sends instructions to the spinal cord to command muscles to move. They also recognized that the two symmetrical hemispheres of the brain are connected by the corpus callosum and can thus interact. (A) Gall’s ideas about behavior began with an obserFigure 1.4 # vation made in his youth. Reportedly, he observed Gall’s Theory Depressions that students with good memories had large, protrud(A) and bumps (B) on the skull indicate the size of the undering eyes and surmised that a well-developed memory lying area of brain and thus, when area of the cortex located behind the eyes would cause correlated with personality traits, them to protrude. Thus, he developed his hypothesis, indicate the part of the brain concalled localization of function, that a different, spetrolling the trait. While examining (B) a patient (who because of her cific brain area controls each kind of behavior. behavior became known as “Gall’s Gall and Spurzheim furthered this idea by collectPassionate Widow”), Gall found a ing instances of individual differences that they rebump at the back of her neck that lated to other prominent features of the head and skull. he thought located the center for “amativeness” in the cerebellum. They proposed that a bump on the skull indicated a (Research from Olin, 1910.) well-developed underlying cortical gyrus and therefore a greater capacity for a particular behavior; a depression in the same area indicated an underdeveloped gyrus and a concomitantly reduced faculty. Gall correlated bumps Thus, just as a person with a good memory had proin the region of the truding eyes, a person with a high degree of musical cerebellum with the brain’s ”amativeness” center. ability, artistic talent, sense of color, combativeness, or mathematical skill would have large bumps in other areas of the skull. Figure 1.4 shows where Gall and Spurzheim located the trait of amativeness (sexiness). A person with a bump there would be predicted to have a strong sex drive, whereas a person low in this trait would have a depression in the same region. Gall and Spurzheim identified a long list of behavioral traits borrowed from the English or Scottish psychology of the time. They assigned each trait to a particular part of the skull and, by inference, to the underlying brain part. Spurzheim called this study of the relation between the skull’s surface features and a person’s mental faculties phrenology (phren is a Greek word for “mind”). Figure 1.5 shows the resulting phrenological map that he and Gall devised. Some people seized on phrenology as a means of making personality assessments. They developed a method called cranioscopy, in which a device was placed around the skull to measure its bumps and depressions. These measures were then correlated with the phrenological map to determine the person’s likely behavioral traits. The faculties described in phrenology— characteristics such as faith, self-love, and veneration—are impossible to define and to quantify objectively. Phrenologists also failed to recognize that the superficial features on the skull reveal little Figure 1.5 ! about the underlying brain. Gall’s notion of localization of function, although inaccurate scientifically, laid the conceptual foundation for Phrenology Bust Originally, Gall’s system identified putative locations for 27 faculties. As modern views of functional localization, beginning with the localizathe study of phrenology expanded, the number tion of language. of faculties increased. Language, indicated at Among his many observations, Gall gave the first account of a the front of the brain, below the eye, actually derived from one of Gall’s case studies. A solcase in which frontal-lobe brain damage was followed by loss of the ability to speak. The patient was a soldier whose brain was pierced dier had received a knife wound that penetrated the frontal lobe of his left hemisphere through by a sword driven through his eye. Note that, on the phrenological the eye. The soldier lost the ability to speak. map in Figure 1.5, language is located below the eye. Gall gave the (Mary Evans Picture Library/Image Works.) 9 10 PART I BACKGROUN D observation no special emphasis, thinking it merely a confirmation of his theory. The case subsequently came to factor in discoveries concerning the brain’s role in language. Lateralization of Function A now legendary chain of observations and speculations led to confirmation that language is both localized in the brain and lateralized, that is, located on one side of the brain. This discovery led to the principle of lateralization of function, that one cerebral hemisphere can perform a function not shared by the other (Benton, 1964). We begin on February 21, 1825, as French physician Jean Baptiste Bouillaud (1796–1881) read a paper before the Royal Academy of Medicine in France. Bouillaud argued from clinical studies that certain functions are localized in the cortex and, specifically, that speech is localized in the frontal lobes, in accordance with Gall’s theory. Observing that acts such as writing, drawing, painting, and fencing are carried out with the right hand, Bouillaud also suggested that the part of the brain that controls them might be the left hemisphere. Physicians had long recognized that damage to a hemisphere of the brain impairs movement of the opposite side of the body. A few years later, in 1836, Marc Dax (1770–1837) presented a paper in Montpellier, France, discussing a series of clinical cases demonstrating that disorders of speech were constantly associated with lesions of the left hemisphere. Dax’s manuscript received little attention, however, and was not published until 1865, by his son. Ernest Auburtin (1825–1893), Bouillaud’s son-in-law, supported Bouillaud’s cause. At a meeting of the Anthropological Society of Paris in 1861, he reported the case of a patient who lost the ability to speak when pressure was applied to his exposed frontal lobe. Auburtin also described another patient, ending with a promise that other scientists interpreted as a challenge: For a long time during my service with M. Bouillaud I studied a patient, named Bache, who had lost his speech but understood everything said to him and replied with signs in a very intelligent manner to all questions put to him. . . . I saw him again recently and his disease has progressed; slight paralysis has appeared but his intelligence is still unimpaired, and speech is wholly abolished. Without a doubt this man will soon die. Based on the symptoms that he presents we have diagnosed softening of the anterior lobes. If, at autopsy, these lobes are found to be intact, I shall renounce the ideas that I have just expounded to you. (Stookey, 1954) Paul Broca, founder of the Society, heard Auburtin’s challenge. Five days later he received a patient, a Monsieur Leborgne, who had lost his speech and was able to say only “tan” and utter an oath. The right side of his body was paralyzed, but he seemed intelligent and typical in other respects. Broca recalled Auburtin’s challenge and invited him to examine Tan, as the patient came to be called. Together they agreed that, if Auburtin was right, Tan should have a frontal lesion. Tan died on April 17, 1861, and the next day Broca (1960) submitted his findings to the Anthropological Society. (This submission is claimed to be the fastest publication ever made in science.) Auburtin was correct: the left frontal CHAPTER 1 THE DEVELOPMENT OF NEUROPSYCHOLOGY §1.3 11 (A) lobe was the focus of Tan’s lesion. By 1863, Broca had collected eight more cases similar to Tan’s, all with a frontal Superior convolution (1st) Middle convolution (2nd) lobe lesion in the left hemisphere (Broca, 1865). Inferior convolution (3rd) As a result of his studies, Broca located speech in the third convolution (gyrus) of the frontal lobe on the left side Broca’s area of the brain (Figure 1.6A). By demonstrating that speech is located only in one hemisphere, Broca discovered the Broca located speech in this brain property of functional lateralization. Because speech area of the frontal lobe. is thought central to human consciousness, the left hemisphere is frequently referred to as the dominant hemisphere (B) to recognize its special role in language (Joynt, 1964). In recognition of Broca’s contribution, the anterior speech region of the brain is called Broca’s area, and the syndrome that results from its damage is called Broca’s aphasia (from the Greek a, for “not,” and phasia, for “speech”). An interesting footnote: Broca examined Tan’s brain (Figure 1.6B) only by inspecting its surface. His anatomical analysis was criticized by French anatomist Pierre Marie (1906), who reexamined the preserved brains of Broca’s first two patients, Tan and Monsieur Lelong, 25 years after Broca’s death. Marie pointed out in his article, “The Third Left Frontal Convolution Figure 1.6 ! Plays No Particular Role in the Function of Language,” that Lelong’s brain Lateralization of showed general nonspecific atrophy, common in senility, and that Tan had Language (A) Broca’s area is additional extensive damage in his posterior cortex that may have accounted located in the posterior third of for his aphasia. the inferior, or third, convolution Broca was aware of Tan’s posterior damage but concluded that, whereas it (gyrus) of the frontal lobe in the left hemisphere. (B) Photograph contributed to his death, the anterior damage had occurred earlier, producing of the left hemisphere of the brain his aphasia. Broca’s view on localization and his discovery of lateralization beof Leborgne (“Tan”), Broca’s came dogma in neuropsychology for the next 100 years, but a dogma tempered first aphasic patient. (Part B, Paul by Pierre Marie’s criticism. Broca’s historic cases: High resolution A Lateralized Language Model German anatomist Carl Wernicke (1848–1904) created the first model of how the brain produces language in 1874. Wernicke was aware that the part of the cortex into which the sensory pathway from the ear projects—the auditory cortex—is located in the temporal lobe behind Broca’s area. He therefore suspected a relation between hearing and speech functioning, and he described cases in which aphasic patients had lesions in this auditory area of the temporal lobe. These patients displayed no opposite-side paralysis. (Broca’s aphasia is frequently associated with paralysis of the right arm and leg, as described for Tan.) They could speak fluently, but what they said was confused and made little sense. (Broca’s patients could not articulate, but they seemed to understand the meaning of words.) Although Wernicke’s patients could hear, they could neither understand nor repeat what was said to them. Wernicke’s syndrome is sometimes called temporal-lobe aphasia or fluent aphasia, to emphasize that the person can say words, but is more frequently called Wernicke’s aphasia. The associated region of the temporal lobe is called Wernicke’s area. Wernicke’s model of language organization in the left hemisphere is illustrated in Figure 1.7A. He proposed that auditory information travels to the temporal lobes from the auditory receptors in the ears. In Wernicke’s area, sounds are processed into auditory images or ideas of objects and stored. From MR imaging of the brains of Leborgne and Lelong, from N. F. Dronkers, O. Plaisant, M. T. Iba-Zizen, and E. A. Cabanis, Brain, Oxford University Press, May 1, 2007.) 12 PART I BACKGROUN D (A) Wernicke’s original model a’ b b’ a (B) Contemporary version of Wernicke’s model 3 …and are sent to Broca‘s area… 2 Arcuate fasciculus Broca’s area Wernicke’s area 4 …for articulation over the motor pathway. Figure 1.7 ! Organization of Language in the Brain (A) In Wernicke’s 1874 model, sounds enter the brain through the auditory pathway (a). Sound images stored in Wernicke’s auditory area (a!) are sent to Broca’s word area (b) for articulation through the motor pathway (b!). Lesions along this route a–a!–b–b!) could produce different types of aphasia, depending on their location. Curiously, Wernicke drew all his language models on the right hemisphere even though he believed that the left hemisphere is the dominant hemisphere for language, and he drew the brain of an ape, which, Wernicke knew, cannot speak. (B) A contemporary rendition of Wernicke’s model. (Part A research from Wernicke, 1874.) Sound images are stored in Wernicke’s area… Wernicke’s area, auditory ideas flow through a pathway, the arcuate fasciculus (from the Latin arc, for “bow,” and fasciculus, for “band of tissue,” because the pathway arcs around the lateral fissure, as shown in Figure 1.7B). The pathway leads to Broca’s area, where representations of speech movements are stored, and may link brain regions related to intelligence (see Figure 16.17). To produce the appropriate sounds, neural instructions are sent from Broca’s area to muscles that control mouth movements. According to Wernicke’s model, if the temporal lobe is damaged, speech movements are preserved in Broca’s area, but the speech makes no sense because the person cannot monitor words. Damage to Broca’s area produces a loss of speech movements without the loss of sound images, and therefore Broca’s aphasia is not accompanied by a loss of understanding. Disconnection From his model, Wernicke also predicted a new language disorder but never saw such a case. He suggested that, if the arcuate fibers connecting the two speech areas were cut, disconnecting the areas but without inflicting damage 1 on either one, a speech deficit that Wernicke described Sound sensations as conduction aphasia would result. In this condition, enter the brain speech sounds and movements are retained, but speech is through the auditory pathway. impaired because it cannot be conducted from one region to the other. The patient would be unable to repeat what is heard. After Wernicke’s prediction was subsequently confirmed, American neurologist Norman Geschwind (1974) updated the speech model (Figure 1.7B) in what is now referred to as the Wernicke-Geschwind model. Wernicke’s idea of disconnection offered investigators a completely new way of viewing symptoms of brain damage by proposing that, although different brain regions have different functions, they are interdependent: to work, they must interact. Just as a washed-out bridge prevents traffic from moving from one side of a river to the other and therefore prevents people from performing complex activities such as commercial transactions or emergency response services, cutting connecting pathways prevents two brain regions from communicating and performing complex functions. Using this same reasoning, in 1892 French neurologist Joseph Dejerine (1849–1917) described a case in which the loss of the ability to read (alexia, meaning “word blindness,” from the Greek lexia, for “word”) resulted from a disconnection between the brain’s visual area and Wernicke’s area. Similarly, Wernicke’s student Hugo Liepmann (1863–1925) showed that an inability to make sequences of movements (apraxia, from the Greek praxis, for “movement”) results from the disconnection of motor areas from sensory areas. Disconnection is important in neuropsychology, first because it predicts that complex behaviors are built up in assembly-line fashion as information collected by sensory systems enters the brain and traverses different structures CHAPTER 1 THE DEVELOPMENT OF NEUROPSYCHOLOGY §1.3 before producing an overt response. Second, disconnecting brain structures by cutting connecting pathways can impair those structures in ways that resemble damage to the structures themselves. Chapter 17 elaborates these ideas. Neuroplasticity In the nineteenth century, the work of French physiologist Pierre Flourens (1794–1867) and, later, the German physiologist Friedrich L. Goltz (1834– 1902) once again challenged the idea that brain functions are localized (Flourens, 1960; Goltz, 1960). Both men created animal models of human clinical cases by removing small regions of cortex. Both expected that the animals would lose specific functions. Flourens found instead that with the passage of time, his animals recovered from their initial impairments to the point that they seemed to behave typically. Thus, an impaired pigeon that would not initially eat or fly with time recovered both abilities. More dramatically, Goltz removed almost the entire cortex and a good deal of underlying brain tissue from three dogs that he studied for 57 days, 92 days, and 18 months, respectively, until each dog died. The dog that survived for 18 months was more active than a typical dog. Its periods of sleep and waking were shorter than normal, but it still panted when warm and shivered when cold. It walked well on uneven ground and was able to regain its balance when it slipped. If placed in an abnormal posture, it corrected its position. After hurting a hind limb on one occasion, this dog trotted on three legs, holding up the injured limb. It was able to orient to touches or pinches on its body and to snap at the object that touched it, although its orientations were not very accurate. If offered meat soaked in milk or meat soaked in bitter quinine, it accepted the first and rejected the second. It responded to light and sounds, although its response thresholds were elevated; that is, its senses were not as acute as those typical of a dog. Although impaired, its recovered abilities clearly suggested that the remaining brainstem could substitute for the cortex. These early experiments actually built the foundation for neuropsychology’s emphases on recovery of function and on promoting recovery by rehabilitation after brain damage, even in extreme circumstances, as illustrated in the Snapshot. Neuropsychologists recognize that, although all function may not be recovered after injury, the brain’s plasticity can be harnessed to produce significant functional improvements. Hierarchical Organization The experiments that Flourens and Goltz conducted made a strong argument against localization of function and even cast doubt on the role of the cortex in behavior. Removing the cortex did not appear to eliminate any function completely, though it seemed to reduce all functions somewhat. An explanation for the apparent disconnect between experiments that support functional localization and those that observe recovery of function is hierarchical organization. English neurologist John Hughlings-Jackson (1835–1911) proposed this principle of cerebral organization in which information is processed serially and organized as a functional hierarchy (1931). Each successively higher level controls more-complex aspects of behavior and does so via the lower levels. 13 14 PART I BACKGROUN D SNAPSHOT The Dilemma in Relating Behavior and Consciousness In his 2007 paper, “Consciousness Without a Cerebral Cortex: A Challenge for Neuroscience and Medicine,” Bjorn Merker reviewed the difficulty in determining what is unconscious and what is conscious behavior. Consider three contrasting cases. Case 1: Marie “Terri” Schiavo, a 26-year-old woman from St. Petersburg, Florida, collapsed in her home in 1990 and experienced respiratory and cardiac arrest. Terri was completely unresponsive, comatose for 3 weeks, and although she did become more responsive, her typical conscious behavior did not return. Terri was diagnosed as being in a persistent vegetative state (PVS): she was alive but unable to communicate or to function independently at even the most basic level because the damage to her brain was so extensive that no recovery could be expected. In 1998, Terri’s husband and guardian, Michael Schiavo, petitioned the courts to remove her gastric feeding tube, maintaining that she would not wish to live with such severe impairment. Terri’s parents, Robert and Mary Schindler, were opposed, citing their belief that Terri’s behavior signaled that she was consciously aware and fighting to recover. Amid a storm of national controversy, Michael Schiavo prevailed. Terri’s feeding tube was removed, and she died 13 days later, on March 31, 2005, at the age of 41. CT scan of a healthy adult brain (left) and a comatose brain (right). (Left: Du Cane Medical Imaging Ltd./Science Source; right: Zephyr/Science Source.) Case 2: Giacino and colleagues (2012) described a 38-year-old man who lingered in a minimally conscious state (MCS) for more than 6 years after an assault. He was occasionally able to utter single words and make a few movements but could not feed himself. As part of a clinical trial (a consensual experiment directed toward developing a treatment), the researchers implanted thin wire electrodes into the man’s brainstem and applied mild electrical stimulation for 12 hours each day. (Section 7.2 details this process of deep brain stimulation.) The patient’s behavior improved dramatically: he could follow commands, feed himself, and even watch television. Case 3. Using MRI, Adrian Owen (2013) recorded the brain’s electrical or metabolic activity to determine whether patients who have been in a vegetative state for years can answer questions. For example, patients are asked to attempt to move a hand or a foot, whether they are in pain, whether their brother’s child is called Thomas, or to imagine playing tennis. As determined from control participants, characteristic changes in brain activity signal the patients’ answers. Not only do such tests indicate level of consciousness but conscious patients also can learn to use their brain activity to control a robot or other brain–computer interface (BCI) and therefore communicate and interact. As detailed in the opening Portrait of Chapter 9, BCIs engage the brain’s electrical signals to direct computer-controlled devices. Such innovations in neuroscience are aiding both in assessing the level of consciousness of patients in apparent vegetative or minimally conscious states and in assisting those patients who are conscious to communicate and exert control over their lives. Giacino, J., J. J. Fins, A. Machado, and N. D. Schiff. Central thalamic deep brain stimulation to promote recovery from chronic posttraumatic minimally conscious state: Challenges and opportunities. Neuromodulation 15:339–349, 2012. Merker, B. Consciousness without a cerebral cortex: A challenge for neuroscience and medicine. Behavioural and Brain Sciences 30:63–134, 2007. Owen, A. M. Detecting consciousness: A unique role for neuroimaging. Annual Review of Psychology 64:109–133, 2013. CHAPTER 1 THE DEVELOPMENT OF NEUROPSYCHOLOGY §1.3 Often, Hughlings-Jackson described the nervous system as having three levels—the spinal cord, the brainstem, and the forebrain—that had developed successively in evolution. But equally often, he assigned no particular anatomical area to a given level. Hughlings-Jackson suggested that diseases or damage that affects the highest levels of the brain hierarchy would produce dissolution, the reverse of evolution: animals would still have a behavioral repertoire, but the behaviors would be simpler, more typical of an animal that had not yet evolved the missing brain structure. This description fits the symptoms displayed by Goltz’s dogs. HughlingsJackson’s theory gave rise to the idea that functions are not simply represented in one location in the brain but are re-represented in the neocortex, in the brainstem, and in the spinal cord, as elaborated in Section 10.3. Thus, understanding a function such as walking requires understanding what each level of organization contributes to that behavior. Multiple Memory Systems People usually describe memory as unitary—as for example, “I have a poor memory.” But the conclusion from more than six decades of study is that many memory systems operate within the brain. Contemporary research on memory began in 1953, when neurosurgeon William B. Scoville removed parts of the temporal lobes from the left and right hemispheres of patient H.M. to treat his epilepsy, a condition characterized by recurrent seizures associated with disturbance of consciousness. The surgery stopped the epilepsy but left H.M. with a severe memory problem: amnesia, partial or total loss of memory (Scoville and Milner, 1957). H.M. was studied for more than 50 years, and more scientific papers have been written about his case than that of any other neuropsychological patient (Corkin, 2000). His case, detailed throughout Chapter 18, reveals that rather than a single memory structure in the brain, a number of neural structures encode memories separately and in parallel. H.M. appeared to have retained memories from before the surgery but was unable to form new memories that endured for more than a few seconds to minutes. Nevertheless, he could acquire motor skills but could not remember having done so. Thus, H.M. and L.D., whose case opens this chapter, both demonstrate that the neural structures for learning motor skills and those for remembering that one has those skills are separate. The study of amnesia suggests that when people have a memorable experience, they encode different parts of the experience in different parts of the brain concurrently. Spatial location is stored in one brain region, emotional content in another, events comprising the experience in still another region, and so on. In fact, nowhere in the brain do all the aspects of the experience come together to form “the memory.” How does the brain tie single and varied sensory and motor events together into a unified perception or behavior, or a memory? This binding problem extends from perceptive to motor to cognitive processes, the different parts of which are mediated by different neural structures. The essence of the puzzle: although the brain analyzes sensory events through multiple parallel channels that do not converge on a single brain region, we perceive a unified experience, such as a memory. We recall a single memory of an event when in fact we have many separate memories, each stored in a different region of the brain. 15 16 PART I BACKGROUN D Two Brains In the early 1960s, to prevent the spread of intractable epileptic seizures from one hemisphere to the other in a number of patients, two neurosurgeons, Joseph Bogen and Phillip Vogel, cut the corpus callosum and the smaller commissures that connect the two cortical hemispheres. Essentially, the surgeries made two brains from one. The surgery was effective in reducing the seizures and in improving the lives of these split-brain patients. Roger W. Sperry conducted a series of studies on them that provided a new view of how each hemisphere functions. By taking advantage of the anatomy of sensory pathways that project preferentially to the opposite hemisphere, Sperry presented information separately to these split-brain patients’ left and right hemispheres. Although mute, the right hemisphere was found to comprehend words spoken aloud, read printed words, point to corresponding objects or pictures in an array, and match presented objects or pictures correctly from spoken to printed words and vice versa. (Sections 11.2 and 17.4 expand on split-brain phenomena.) In his Nobel lecture, Sperry (1981) concluded that each hemisphere possesses complementary self-awareness and social consciousness and that much of internal mental life, especially in the right hemisphere, is inaccessible to analysis using spoken language. Sperry proposed that a neuropsychology that does not accept the existence of a private mental life and relies solely on quantitative, objective measurement of behavior cannot fully understand a brain in which inner experience itself is causal in expressing overt behavior. Conscious and Unconscious Neural Streams In February 1988, near Milan, Italy, D.F. was poisoned by carbon monoxide (CO) emitted by a faulty space heater. As the CO replaced the oxygen in her blood, D.F.’s brain was deprived of oxygen, and she sank into a coma. When she recovered consciousness in the hospital, D.F. was alert, could speak and understand, but could see nothing. The diagnosis of her cortical blindness resulted from damage to the visual cortex at the back of the occipital lobe rather than to any problem with her eyes. D.F. eventually regained some vision: she could see color and even identify what objects were made of by their color. Her deficit was visual form agnosia: she could not see the shapes of objects nor recognize objects visually by their shape. D.F.’s visual acuity was normal, but she could not distinguish vertical lines from horizontal lines. She could not recognize objects or drawings of objects. She could draw objects from memory but could not recognize the objects she had drawn. One day in a clinical setting in St. Andrews, Scotland, Scottish neuropsychologist David Milner and Canadian neuropsychologist Melvyn Goodale observed that D.F. accurately reached for and grasped a pencil that they offered her. Nevertheless, she could not see the pencil or tell whether its orientation was horizontal or vertical. D.F.’s ability to perform this act presented a paradox. How could she reach out to grasp the pencil when, at the same time, she could not tell the neuropsychologists what she saw? In further tests, D.F. demonstrated that she could shape her hand correctly to grasp many objects that she could not recognize, and even step over objects that she could not see. In sum, D.F. appears able to see if she is required to move CHAPTER 1 THE DEVELOPMENT OF NEUROPSYCHOLOGY §1.4 17 to perform an action; otherwise, she is blind to the form of objects. (D.F.’s case is featured in Section 13.4.) D.F.’s visual agnosia stands in contrast to the deficits displayed by patients whose visual ataxia (taxis, meaning “to move toward”) leads them to make errors in reaching for objects while still being able to describe the objects accuParietal Frontal rately. The brain lesions in agnosia patients such as D.F. occur in neural lobe lobe structures that constitute a pathway, called the ventral stream, from the Occipital visual cortex to the temporal lobe for object identification. Brain lesions lobe D ors in patients with optic ataxia are in neural structures that form a pathway al str from the visual cortex to the parietal cortex called the dorsal stream to ea m guide action relative to objects (Figure 1.8). Ventral stream Goodale and Milner (2004) proposed that the ventral stream mediates actions controlled by conscious visual perception, whereas the dorVisual Temporal sal stream mediates actions controlled by unconscious visual processes. cortex lobe Although we believe that we are consciously guiding our visual actions, much of what vision does for us lies outside our conscious visual experience Figure 1.8 ! and essentially uses computations that are robotic in nature. Thus, vision, like Neural Streams The dorsal language and memory, is not unitary. and ventral streams mediate It follows that other sensory systems are not unitary but rather consist of vision for action and for recogniseparate pathways that mediate unconscious or conscious actions. Neverthetion, respectively. less, we experience a seamless, binding interaction between conscious and unconscious action. We see the world, and ourselves, as whole, so much so that subsequent to brain damage, such as L.D.’s traumatic brain injury described in the chapter’s Portrait, people may not be aware of their behavioral deficits. The paradox posed by the discovery of conscious and unconscious vision is that in its goal to account for our conscious behavior, neuropsychology must also identify and account for our unconscious behavior. 1.4 The Neuron Theory Alongside the brain theory, the idea that the brain is responsible for all behavior, the second major source of findings that influences modern neuropsychology is the neuron theory, the idea that the unit of brain structure and function is the nerve cell. In this section, we introduce the three aspects of the neuron theory: (1) neurons are discrete, autonomous cells that interact but are not physically connected; (2) neurons send electrical signals that have a chemical basis; and (3) neurons use chemical signals to communicate with one another. Nervous System Cells The nervous system is composed of two classes of cells, neurons and glia (from the Greek word for “glue”). Neurons produce our behavior and mediate the