Chapter 2: Cognitive Neuroscience PDF

Page 1 of 16 CHAPTER 2: COGNITIVE NEUROSCIENCE Cognitive neuroscience is the field of study linking the brain and other aspects of the nervous system to cognitive processing and, ultimate...

Page 1 of 16 CHAPTER 2: COGNITIVE NEUROSCIENCE Cognitive neuroscience is the field of study linking the brain and other aspects of the nervous system to cognitive processing and, ultimately, to behavior. The brain is the organ in our bodies that most directly controls our thoughts, emotions, and motivations (Gloor, 1997; Rockland, 2000; Shepherd, 1998). Figure 2.1 shows photos of what the brain looks like. We usually think of the brain as being at the top of the body’s hierarchy—as the boss, with various other organs responding to it. Like any good boss, however, it listens to and is influenced Figure 2.1 The Human Brain by its subordinates, the other organs of the body. Thus, the brain is reactive as well as directive. A major goal of present research on the brain is to study localization of function. Localization of function refers to the specific areas of the brain that control specific skills or behaviors. Cognition in the Brain: The Anatomy and Mechanisms of the Brain The nervous system is the basis for our ability to perceive, adapt to, and interact with the world around us (Gazzaniga, 1995, 2000; Gazzaniga, Ivry, & Mangun, 1998). Through this system we receive, process, and then respond to information from the environment (Pinker, 1997a; Rugg, 1997). Gross Anatomy of the Brain: Forebrain, Midbrain, Hindbrain The brain has three major regions: forebrain, midbrain, and hindbrain. These labels do not correspond exactly to locations of regions in an adult or even a child’s head. Rather, the terms come from the front-to-back physical arrangement of these parts in the nervous system of a developing embryo. Initially, the forebrain is generally the farthest forward, toward what becomes the face. The midbrain is next in line. And the hindbrain is generally farthest from the forebrain, near the back of the neck. In Figure 2.2 Fetal Brain Development development, the relative orientations change so that the forebrain is almost a cap on top of the midbrain and hindbrain. Nonetheless, the terms still are used to designate areas of the fully developed brain. Figures 2.2 shows the changing locations and relationships of the forebrain, the midbrain, and the hindbrain over the course of development of the brain. You can see how they develop, from an embryo a few weeks after conception to a fetus of seven months of age. Divisions of the Brain: Forebrain, Midbrain, Hindbrain While there are a few different ways to divide the brain, the developmental division roughly organizes the brain into three general regions: forebrain (also known as the prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon). The forebrain is home to sensory processing, endocrine structures, and higher reasoning. The midbrain plays a role in motor movement and audio/visual processing. The hindbrain is involved with autonomic Figure 2.3 Divisions of the Brain  Page 2 of 16 functions such as respiratory rhythms and sleep. The Forebrain (Prosencephalon) The forebrain is the region of the brain located toward the top and front of the brain. It comprises the cerebral cortex, the basal ganglia, the limbic system, the thalamus, and the hypothalamus (Figure 2.4). The cerebral cortex is the outer layer of the cerebral hemispheres. It plays a vital role in our thinking and other mental processes. Figure 2.4 Structures of the Brain The basal ganglia (singular: ganglion) are collections of neurons crucial to motor function. Dysfunction of the basal ganglia can result in motor deficits. These deficits include tremors, involuntary movements, changes in posture and muscle tone, and slowness of movement. Deficits are observed in Parkinson’s disease and Huntington’s disease. Both these diseases entail severe motor symptoms (Rockland, 2000; Lerner & Riley, 2008; Lewis & Barker, 2009). The limbic system is important to emotion, motivation, memory, and learning. Animals such as fish and reptiles, which have relatively undeveloped limbic systems, respond to the environment almost exclusively by instinct. Mammals and especially humans have relatively more developed limbic systems. Our limbic system allows us to suppress instinctive responses (e.g., the impulse to strike someone who accidentally causes us pain). Our limbic systems help us to adapt our behaviors flexibly in response to our changing environment. The limbic system comprises three central interconnected cerebral structures: the septum, the amygdala, and the hippocampus. The septum is involved in anger and fear. The amygdala plays an important role in emotion as well, especially in anger and aggression (Adolphs, 2003; Derntl et al., 2009). Stimulation of the amygdala commonly results in fear. It can be evidenced in various ways, such as through palpitations, fearful hallucinations, or frightening flashbacks in memory (Engin & Treit, 2008; Gloor, 1997; Rockland, 2000). Damage to (lesions in) or removal of the amygdala can result in maladaptive lack of fear. In the case of lesions to the animal brain, the animal approaches potentially dangerous objects without hesitation or fear (Adolphs et al., 1994; Frackowiak et al., 1997). The amygdala also has an enhancing effect for the  Page 3 of 16 perception of emotional stimuli. In humans, lesions to the amygdala prevent this enhancement (Anderson & Phelps, 2001; Tottenham, Hare, & Casey, 2009). Additionally, persons with autism display limited activation in the amygdala. A well-known theory of autism suggests that the disorder involves dysfunction of the amygdala, which leads to the social impairment that is typical of persons with autism, for example, difficulties in evaluating people’s trustworthiness or recognizing emotions in faces (Adolphs, Sears, & Piven, 2001; Baron-Cohen et al., 2000; Howard et al., 2000; Kleinhans et al., 2009) Two other effects of lesions to the amygdala can be visual agnosia (inability to recognize objects) and hypersexuality (Steffanaci, 1999). The hippocampus plays an essential role in memory formation (Eichenbaum, 1999, 2002; Gluck, 1996; Manns & Eichenbaum, 2006; O’Keefe, 2003). It gets its name from the Greek word for “seahorse,” its approximate shape. The hippocampus is essential for flexible learning and for seeing the relations among items learned as well as for spatial memory (Eichenbaum, 1997; Squire, 1992). The hippocampus also appears to keep track of where things are and how these things are spatially related to each other. In other words, it monitors what is where (Cain, Boon, & Corcoran, 2006; Howland et al., 2008; McClelland et al., 1995; Tulving & Schacter, 1994). People who have suffered damage to or removal of the hippocampus still can recall existing memories—for example, they can recognize old friends and places— but they are unable to form new memories (relative to the time of the brain damage). New information—new situations, people, and places—remain forever new. A disease that produces loss of memory function is Korsakoff’s syndrome. Other symptoms include apathy, paralysis of muscles controlling the eye, and tremor. This loss is believed to be associated with deterioration of the hippocampus and is caused by a lack of thiamine (Vitamin B-1) in the brain. The syndrome can result from excessive alcohol use, dietary deficiencies, or eating disorders. There is a renowned case of a patient known as H.M., who after brain surgery retained his memory for events that transpired before the surgery but had no memory for events after the surgery. This case is another illustration of the resulting problems with memory formation due to hippocampus damage Disruption in the hippocampus appears to result in deficits in declarative memory (i.e., memory for pieces of information), but it does not result in deficits in procedural memory (i.e., memory for courses of action) (Rockland, 2000). The thalamus relays incoming sensory information through groups of neurons that project to the appropriate region in the cortex. Most of the sensory input into the brain passes through the thalamus, which is approximately in the center of the brain, at about eye level. To accommodate all the types of information that must be sorted out, the thalamus is divided into a number of nuclei (groups of neurons of similar function). Each nucleus receives information from specific senses. The information is then relayed to corresponding specific areas in the cerebral cortex. The thalamus also helps in the control of sleep and waking. When the thalamus malfunctions, the result can be pain, tremor, amnesia, impairment of language, and disruptions in waking and sleeping (Rockland, 2000; Steriade, Jones, & McCormick, 1997). In cases of schizophrenia, imaging and in vivo studies reveal abnormal changes in the thalamus (Clinton & Meador-Woodruff, 2004). These abnormalities result in difficulties in filtering stimuli and focusing attention, which in turn can explain why people suffering from schizophrenia experience symptoms such as hallucinations and delusions. The Midbrain The midbrain helps to control eye movement and coordination. The midbrain is more important in nonmammals where it is the main source of control for visual and auditory information. In mammals these functions are dominated by the forebrain. By far the most indispensable of these structures is the reticular activating system (RAS; also called the “reticular formation”), a network of neurons essential to the regulation of consciousness (sleep; wakefulness; arousal; attention to some extent; and vital functions such as heartbeat and breathing; Sarter, Bruno, & Berntson, 2003).  Page 4 of 16 The RAS also extends into the hindbrain. Both the RAS and the thalamus are essential to our having any conscious awareness of or control over our existence. The brainstem connects the forebrain to the spinal cord. It comprises the hypothalamus, the thalamus, the midbrain, and the hindbrain. A structure called the periaqueductal gray (PAG) is in the brainstem. This region seems to be essential for certain kinds of adaptive behaviors. Injections of small amounts of excitatory amino Figure 2.5 The acids or,of alternatively, Structure Midbrain electrical stimulation of this area results in any of several responses: an aggressive, confrontational response; avoidance or flight response; heightened defensive reactivity; or reduced reactivity as is experienced after a defeat, when one feels hopeless (Bandler & Shipley, 1994; Rockland, 2000). Physicians decide of brain death based on the function of the brainstem. Specifically, a physician must determine that the brainstem has been damaged so severely that various reflexes of the head (e.g., the pupillary reflex) are absent for more than 12 hours, or the brain must show no electrical activity or cerebral circulation of blood (Berkow, 1992). The Hindbrain The hindbrain comprises the medulla oblongata, the pons, and the cerebellum. The medulla oblongata controls heart activity and largely controls breathing, swallowing, and digestion. The medulla is also the place at which nerves from the right side of the body cross over to the left side of the brain and nerves from the left side of the body cross over to the right side of the brain. The medulla oblongata is an elongated interior structure located at the point where the spinal cord enters the skull and joins with the brain. The medulla oblongata, which contains part of the RAS, helps to keep us alive. Figure 2.6 The Structure of Hindbrain The pons serves as a kind of relay station because it contains neural fibers that pass signals from one part of the brain to another. Its name derives from the Latin for “bridge,” as it serves a bridging function. The pons also contains a portion of the RAS and nerves serving parts of the head and face. The cerebellum (from Latin, “little brain”) controls bodily coordination, balance, and muscle tone, as well as some aspects of memory involving procedure-related movements (Middleton & Helms Tillery, 2003). The prenatal development of the human brain within each individual roughly corresponds to the evolutionary development of the human brain within the species as a whole. Specifically, the hindbrain is evolutionarily the oldest and most primitive part of the brain. It also is the first part of the brain to develop prenatally. The midbrain is a relatively newer addition to the brain in evolutionary terms. It is the next part of the brain to develop prenatally. Finally, the forebrain is the most recent evolutionary addition to the brain. It is the last of the three portions of the brain to develop prenatally. Additionally, across the evolutionary development of our species, humans have shown an increasingly greater proportion of brain weight in relation to body weight. However, across the span of development after birth, the proportion of brain weight to body weight declines. For cognitive psychologists, the most important of these evolutionary trends is the increasing neural complexity of the brain. The evolution of the human brain has offered us the enhanced ability to exercise voluntary control over behavior. It has also strengthened our ability to plan and to contemplate alternative courses of action. These ideas are discussed in the next section with respect to the cerebral cortex. Cerebral Cortex and Localization of Function The cerebral cortex is composed of a complex association of tightly packed neurons covering the outermost portion of the brain. It is the gray matter of the brain. Lying right under the meninges, the cerebral cortex divides into four lobes: frontal, temporal, parietal and occipital lobes, each with a multitude of functions. It is characteristically known for its bulges of brain tissue known as gyri, alternating with deep fissures known as sulci. The enfolding of the brain is an adaptation to the dramatic growth in brain size during evolution. The various folding of brain tissue allowed large brains to fit in relatively small cranial vaults that had to remain small to accommodate the birth process. Notable sulci include the Sylvian fissure which divides the temporal lobe from the frontal and  Page 5 of 16 parietal lobe, the central sulcus which separates the frontal and parietal lobes, the parieto-occipital sulcus which divides the parietal and occipital lobes, and the Figure 2.7 The Cerebral Cortex calcarine sulcus which divides the cuneus from the lingual gyrus. The cerebral cortex contains sensory, motor and important association areas. The thalamus receives somatosensory information and conveys it to the primary somatosensory cortex in the postcentral gyrus of the parietal lobe. Other important primary cortical sensory areas include the temporal lobe auditory cortex and the occipital lobe visual cortex. Each sensory area has associated sensations given specific stimuli, providing meaning to sensations. The motor regions of the cerebral cortex are located predominantly in the frontal lobe, anterior to the central sulcus, and include the primary motor cortex (found in the precentral gyrus) and the premotor cortex, which initiates and regulates voluntary movement. Structure and Function The frontal lobe is the largest lobe of the brain, lying in front of the central sulcus. Both anatomically and functionally, it divides into different significant areas. The dorsolateral frontal lobe is divided into three major areas which include the prefrontal cortex, the premotor cortex, and the primary motor cortex. Damage to any of these areas may lead to weakness and impaired execution of motor tasks of the contralateral side. The inferolateral areas of the dominant hemisphere (usually left side) of the frontal lobe are the expressive language area (Broca area, Brodmann areas 44 and 45), to which damage will result in a non-fluent expressive type of aphasia. Other frontal lobe areas including the orbitofrontal area and the medial frontal area are involved in a variety of higher functioning processing, such as regulating emotions, social interactions, and personality. The medial frontal cortex is also the central brain micturition center. The frontal lobes are critical for more difficult decisions and interactions that are essential for human behavior. Thus, damage to this area may result in disinhibition and deficits in concentration, orientation, and judgment. A frontal lobe lesion may also result in regression or a re- emergence of primitive reflexes. The frontal eye fields are the central saccadic eye movement control area, damage to this area may cause eye deviation towards the side of the lesion. However, in patients experiencing a seizure arising from the frontal eye fields will result in the eyes to look away from the lesion. Temporal Lobe The temporal lobe processes sensory input into derived meanings for the appropriate retention of emotions, visual memory, and language comprehension. It contains the primary auditory cortex which is involved in processing sound. Wernicke's area is located in the superior temporal gyrus of the dominant hemisphere and manages the comprehension of language. A lesion affecting the superior temporal gyrus will result in receptive aphasia; the person will have fluent speech that makes no sense. The medial temporal lobe consists of important neural structures such as the parahippocampal gyrus, uncus, hippocampus, temporal horn, and choroidal fissure. A lesion in the hippocampus can cause anterograde amnesia and the inability to make new memories. The medial temporal lobe is the primary epileptogenic area of the brain. Seizures originating from these areas not only can affect emotions but can also result in deja-vu or olfactory hallucinations. Bilateral lesions in the amygdala such as in Herpes simplex encephalitis may cause Kluver-Bucy syndrome. In this syndrome, patients would experience dis-inhibited behavior such as hyperphagia, hypersexuality, and hyper-orality. The inferior portion of the optic radiation passes through the temporal lobe. Damage to this part of the white matter tract may cause a superior quadrantic visual field defect commonly called pie in the sky defect. The posteromedial temporal lobes are the "what" visual association areas. Bilateral damage may result in acquired color blindness (achromatopsia). Parietal Lobe The parietal lobe is responsible for perception, sensation, and integrating sensory input with the visual system. It houses the primary somatosensory cortex, which is located in the postcentral gyrus, posterior to  Page 6 of 16 the central sulcus. It is responsible for receiving contralateral sensory information. Damage to the dominant parietal cortex (usually left) leads to Gerstmann's syndrome. Characteristics of this syndrome include difficulty with writing (agraphia), difficulty with mathematics (acalculia), finger agnosia, and left- right disorientation. Damage to the non-dominant parietal lobe (usually right) leads to agnosia of the contralateral side of the world, also known as hemispatial neglect syndrome. Patients with lesions in the non-dominant parietal lobe exhibit difficulty with self-care such as dressing and washing. Bilateral damage to the "where" visual association areas of the lateral parietal lobe is known as Balint's syndrome, which is characterized by an inability to voluntarily control the gaze (ocular apraxia), inability to integrate components of a visual scene (simultagnosia), and the inability to accurately reach for an object with visual guidance (optic ataxia). Occipital Lobe The occipital lobe is associated with visual processing (De Weerd, 2003b). The occipital lobe contains numerous visual areas, each specialized to analyze specific aspects of a scene, including color, motion, location, and form (Gazzaniga, Ivry, & Mangun, 2002). When you go to pick strawberries, your occipital lobe is involved in helping you find the red strawberries in between the green leaves.The occipital lobe is the center for the processing of visual input in humans. The primary visual cortex is located in Brodmann Area 17, on the medial side of the occipital lobe within the calcarine sulcus. Damage to a single occipital lobe can result in homonymous hemianopsia as well as visual hallucinations. Bilateral damage to the primary visual cortex can cause blindness (cortical blindness). Clinically it is characterized by loss of sight with preserved light reflexes. Denial of visual loss in cortical blindness is characteristic of Anton syndrome. The patient may also experience visual illusions in which objects would appear larger/smaller than they actually are, or objects appear with abnormal coloration. Neuroanatomical Directional Terms The brain is a very complex structure, and researchers use a variety of expressions to describe which part of the brain they are speaking of. Figure 2.8 explains some other words that are frequently used to describe different brain regions. These are the words rostral, ventral, caudal, and dorsal. They are all derived from Latin words and indicate the part of the brain with respect to other body parts. Rostral refers to the front part of the brain (literally the “nasal region”). Ventral refers to the bottom surface of the body/brain (the side of the stomach). Caudal literally means “tail” and Figure 2.8 Neuroanatomical Directional Terms refers to the back part of the body/brain. Dorsal refers to the upside of the brain (it literally means “back,” and in animals the back is on the upside of the body). The brain typically makes up only one fortieth of the weight of an adult human body. Nevertheless, it uses about one fifth of the circulating blood, one fifth of the available glucose, and one fifth of the available oxygen. It is, however, the supreme organ of cognition. Understanding both its structure and function, from the neural to the cerebral levels of organization, is vital to an understanding of cognitive psychology. The recent development of the field of cognitive neuroscience, with its focus on localization of function, reconceptualizes the mind–body question discussed in the beginning of this chapter. The question has changed from “Where is the mind located in the body?” to “Where are particular cognitive operations located in the nervous system?” Neuronal Structure and Function To understand how the entire nervous system processes information, we need to examine the structure and function of the cells that constitute the nervous system. Individual neural cells, called neurons, transmit electrical signals from one location to another in the nervous system (Carlson, 2006; Shepherd, 2004). The greatest concentration of neurons is in the neocortex of the brain. The neocortex is  Page 7 of 16 the part of the brain associated with complex cognition. This tissue can contain as many as 100,000 neurons per cubic millimeter (Churchland & Sejnowski, 2004). The neurons tend to be arranged in the form of networks, which provide information and feedback to each other within various kinds of information processing (Vogels, Rajan, & Abbott, 2005). Neurons vary in their structure, but almost all neurons have four basic parts, as illustrated in Figure 2.9. These include a soma (cell body), dendrites, an axon, and terminal buttons. Figure 2.9 The Structure of Neurons The soma, which contains the nucleus of the cell (the center portion that performs metabolic and reproductive functions for the cell), is responsible for the life of the neuron and connects the dendrites to the axon. The many dendrites are branchlike structures that receive information from other neurons, and the soma integrates the information. Learning is associated with the formation of new neuronal connections. Hence, it occurs in conjunction with increased complexity or ramification in the branching structure of dendrites in the brain. The single axon is a long, thin tube that extends (and sometimes splits) from the soma and responds to the information, when appropriate, by transmitting an electrochemical signal, which travels to the terminus (end), where the signal can be transmitted to other neurons. Axons are of two basic, roughly equally occurring kinds, distinguished by the presence or absence of myelin. Myelin is a white, fatty substance that surrounds some of the axons of the nervous system, which accounts for some of the whiteness of the white matter of the brain. Some axons are myelinated (in that they are surrounded by a myelin sheath). This sheath, which insulates and protects longer axons from electrical interference by other neurons in the area, also speeds up the conduction of information. In fact, transmission in myelinated axons can reach 100 meters per second (equal to about 224 miles per hour). Moreover, myelin is not distributed continuously along the axon. It is distributed in segments broken up by nodes of Ranvier. Nodes of Ranvier are small gaps in the myelin coating along the axon, which serve to increase conduction speed even more by helping to create electrical signals, also called action potentials, which are then conducted down the axon. The degeneration of myelin sheaths along axons in certain nerves is associated with multiple sclerosis, an autoimmune disease. It results in impairments of coordination and balance. In severe cases this disease is fatal. The second kind of axon lacks the myelin coat altogether. Typically, these unmyelinated axons are smaller and shorter (as well as slower) than the myelinated axons. As a result, they do not need the increased conduction velocity myelin provides for longer axons (Giuliodori & DiCarlo, 2004). The terminal buttons are small knobs found at the ends of the branches of an axon that do not directly touch the dendrites of the next neuron. Rather, there is a very small gap, the synapse. The synapse  Page 8 of 16 serves as a juncture between the terminal buttons of one or more neurons and the dendrites (or sometimes the soma) of one or more other neurons (Carlson, 2006). Synapses are important in cognition. Rats show increases in both the size and the number of synapses in the brain as a result of learning (Federmeier, Kleim & Greenough, 2002). Decreased cognitive functioning, as in Alzheimer’s disease, is associated with reduced efficiency of synaptic transmission of nerve impulses (Selkoe, 2002). Signal transmission between neurons occurs when the terminal buttons release one or more neurotransmitters at the synapse. These neurotransmitters are chemical messengers for transmission of information across the synaptic gap to the receiving dendrites of the next neuron (von Bohlen und Halbach & Dermietzel, 2006). Although scientists have identified more than 100 transmitter substances, it seems likely that more remain to be discovered. Medical and psychological researchers are working to discover and understand neurotransmitters. In particular, they wish to understand how the neurotransmitters interact with drugs, moods, abilities, and perceptions. We know much about the mechanics of impulse transmission in nerves. But we know relatively little about how the nervous system’s chemical activity relates to psychological states. Despite the limits on present knowledge, we have gained some insight into how several of these substances affect our psychological functioning. At present, it appears that three types of chemical substances are involved in neurotransmission: monoamine neurotransmitters are synthesized by the nervous system through enzymatic actions on one of the amino acids (constituents of proteins, such as choline, tyrosine, and tryptophan) in our diet (e.g., acetylcholine, dopamine, and serotonin); amino-acid neurotransmitters are obtained directly from the amino acids in our diet without further synthesis (e.g., gamma-aminobutyric acid, or GABA); neuropeptides are peptide chains (molecules made from the parts of two or more amino acids). Table 2.1 lists some examples of neurotransmitters, together with their typical functions in the nervous system and their associations with cognitive processing. Table 2.1 Neurotransmitters Receptors and Drugs Receptors in the brain that normally are occupied by the standard neurotransmitters can be hijacked by psychopharmacologically active drugs, legal or illegal. In such cases, the molecules of the  Page 9 of 16 drugs enter into receptors that normally would be for neurotransmitter substances endogenous in (originating in) the body. When people stop using the drugs, withdrawal symptoms arise. Once a user has formed narcotic dependence, for example, the form of treatment differs for acute toxicity (the damage done from a particular overdose) versus chronic toxicity (the damage done by long-term drug addiction). Acute toxicity is often treated with naloxone or related drugs. Naloxone (as well as a related drug, naltrexone) occupies opiate receptors in the brain better than the opiates themselves occupy those sites; thus, it blocks all effects of narcotics. In fact, naloxone has such a strong affinity for the endorphin receptors in the brain that it actually displaces molecules of narcotics already in these receptors and then moves into the receptors. Naloxone is not addictive, however. Even though it binds to receptors, it does not activate them. Although naloxone can be a life-saving drug for someone who has overdosed on opiates, its effects are short-lived. Thus, it is a poor long-term treatment for drug addiction. In narcotic detoxification, methadone often is substituted for narcotics (typically, heroin). Methadone binds to endorphin receptor sites in a similar way to naloxone and reduces the heroin cravings and withdrawal symptoms of addicted persons. After the substitution, gradually decreasing dosages are administered to the patient until he or she is drug-free. Unfortunately, the usefulness of methadone is limited by the fact that it is addictive. Viewing the Structures and Functions of the Brain Scientists can use many methods for studying the human brain. These methods include both postmortem (from Latin, “after death”) studies and in vivo (from Latin, “living”) techniques on both humans and animals. Each technique provides important information about the structure and function of the human brain. Even some of the earliest postmortem studies still influence our thinking about how the brain performs certain functions. However, the recent trend is to focus on techniques that provide information about human mental functioning as it is occurring. This trend is in contrast to the earlier trend of waiting to find people with disorders and then studying their brains after they died. Because postmortem studies are the foundation for later work, we discuss them first. We then move on to the more modern in vivo techniques. Postmortem Studies Postmortem studies and the dissection of brains have been done for centuries. Even today, researchers often use dissection to study the relation between the brain and behavior. In the ideal case, studies start during the lifetime of a person. Researchers observe and document the behavior of people who show signs of brain damage while they are alive (Wilson, 2003). Later, after the patients die, the researchers examine the patients’ brains for lesions—areas where body tissue has been damaged, such as from injury or disease. Then the researchers infer that the lesioned locations may be related to the behavior that was affected. Through such investigations, researchers may be able to trace a link between an observed type of behavior and anomalies in a particular location in the brain. An early example is Paul Broca’s (1824– 1880) famous patient, Tan (so named because that was the only syllable he was capable of uttering). Tan had severe speech problems. These problems were linked to lesions in an area of the frontal lobe (Broca’s area). This area is involved in certain functions of speech production. In more recent times, postmortem examinations of victims of Alzheimer’s disease (an illness that causes devastating losses of memory; see Chapter 5) have led researchers to identify some of the brain structures involved in memory (e.g., the hippocampus, described earlier in this chapter). These examinations also have identified some of the microscopic aberrations associated with the disease process (e.g., distinctive tangled fibers in the brain tissue). Although lesioning techniques provide the basic foundation for understanding the relation of the brain to behavior, they are limited in that they cannot be performed on the living brain. As a result, they do not offer insights into more specific physiological processes of the brain. For this kind of information, we need to study live nonhuman animals. Studying Live Nonhuman Animals Scientists also want to understand the physiological processes and functions of the living brain. To study the changing activity of the living brain, scientists must use in vivo research. Many early in vivo techniques were performed exclusively on animals. For example, Nobel Prize–winning research on visual  Page 10 of 16 perception arose from in vivo studies investigating the electrical activity of individual cells in particular regions of the brains of animals (Hubel & Wiesel, 1963, 1968, 1979; see Chapter 3). To obtain single-cell recordings, researchers insert a very thin electrode next to a single neuron in the brain of an animal (usually a monkey or a cat). They then record the changes in electrical activity that occur in the cell when the animal is exposed to a stimulus. In this way, scientists can measure the effects of certain kinds of stimuli, such as visually presented lines, on the activity of individual neurons. Neurons fire constantly, even if no stimuli are present, so the task of the researcher is to find stimuli that produce a consistent change in the activity of the neuron. This technique can be used only in laboratory animals, not in humans, because no safe way has yet been devised to perform such recordings in humans. A second group of animal studies includes selective lesioning—surgically removing or damaging part of the brain—to observe resulting functional deficits (Al’bertin, Mulder, & Wiener, 2003; Mohammed, Jonsson, & Archer, 1986). In recent years, researchers have found neurochemical ways to induce lesions in animals’ brains by administering drugs that destroy only cells that use a particular neurotransmitter. Some drugs’ effects are reversible, so that conductivity in the brain is disrupted only for a limited amount of time (Gazzaniga, Ivry, & Mangun, 2009). A third way of doing research with animals is by employing genetic knockout procedures. By using genetic manipulations, animals can be created that lack certain kinds of cells or receptors in the brain. Comparisons with normal animals then indicate what the function of the missing receptors or cells may be. Studying Live Humans Obviously, many of the techniques used to study live animals cannot be used on human participants. Generalizations to humans based on these studies are therefore somewhat limited. However, an array of less invasive imaging techniques for use with humans has been developed. These techniques—electrical recordings, static imaging, and metabolic imaging—are described in this section. Electroencephalogram (EEG) An electroencephalogram (EEG) is a test that measures electrical activity in the brain. This test also is called an EEG. The test uses small, metal discs called electrodes that attach to the scalp. Brain cells communicate via electrical impulses, and this activity shows up as wavy lines on an EEG recording. Brain cells are active all the time, even during sleep. An EEG is one of the main tests to help diagnose epilepsy. An EEG also can play a role in diagnosing other brain conditions. An EEG can find changes in brain activity that might aid in diagnosing brain conditions, especially epilepsy or another seizure condition. An EEG also might be helpful for diagnosing or treating: Brain tumors. Brain damage from a head injury. Brain disease that can have a variety of causes, known as encephalopathy. Inflammation of the brain, such as herpes encephalitis. Stroke. Sleep conditions. Creutzfeldt-Jakob disease. An EEG also might be used to confirm brain death in someone in a coma. A continuous EEG is used to help find the right level of anesthesia for someone in a medically induced coma.  Page 11 of 16 Static Imaging Techniques Cerebral Angiogram A cerebral angiogram is a diagnostic procedure that can reveal any issues with the blood vessels in your brain. Specially trained healthcare providers perform this procedure in an operating room. During the procedure, a provider inserts a catheter (thin plastic tube) into an artery in your wrist or groin area. They then inject a contrast material (a special dye) through the catheter to show the structure of your blood vessels. Next, the provider takes X-rays of your blood vessels while you lay on the procedure table. Cerebral angiograms can provide much more detailed images of these blood vessels than other imaging tests, like CT (computed tomography) or MRI (magnetic resonance imaging) scans. Cerebral angiograms are also called digital subtraction angiography of the brain (DSA). Sometimes, cerebral angiograms only have a diagnostic purpose. At other times, they allow healthcare providers to treat certain conditions. Providers use cerebral angiograms for several reasons. One purpose is to diagnose or confirm blood vessel abnormalities in your brain, including: Brain aneurysm. Atherosclerosis. Arteriovenous malformation. Dural arteriovenous fistula. Vasculitis. Vascular dissection (when the inside wall of an artery tears). Stroke (blood clot). Other uses include: To evaluate arteries in your head and neck before surgery or other medical treatments for your brain, head or neck. To see how blood vessels are connected to or “feeding” a brain tumor. To learn more information about abnormalities providers saw on other imaging tests, such as an MRI or CT scan. Computerized Tomography Scan – CT Scan  Page 12 of 16 A Computerized tomography scan, also called a CT scan, is a type of imaging that uses X-ray techniques to create detailed images of the body. It then uses a computer to create cross-sectional images, also called slices, of the bones, blood vessels and soft tissues inside the body. CT scan images show more detail than plain X-rays do. A CT scan has many uses. It's used to diagnose disease or injury as well as to plan medical, surgical or radiation treatment. Your healthcare professional may suggest a CT scan for many reasons. For instance, a CT scan can help: Diagnose muscle and bone conditions, such as bone tumors and breaks, also called fractures. Show where a tumor, infection or blood clot is. Guide procedures such as surgery, biopsy and radiation therapy. Find and watch the progress of diseases and conditions such as cancer, heart disease, lung nodules and liver masses. Watch how well certain treatments, such as cancer treatment, work. Find injuries and bleeding inside the body that can happen after trauma. Magnetic Resonance Imaging (MRI) The magnetic resonance imaging (MRI) scan is of great interest to cognitive psychologists (Figure 2.11). The MRI reveals high-resolution images of the structure of the living brain by computing and analyzing magnetic changes in the energy of the orbits of nuclear particles in the molecules of the body. There are two kinds of MRIs—structural MRIs and functional MRIs. Structural MRIs provide images of the brain’s size and shape whereas functional MRIs visualize the parts of the brain that are activated when a person is engaged in a particular task. MRIs allow for a much clearer picture of the brain than CT scans. A strong magnetic field is passed through the brain of a patient. A scanner detects various patterns of electromagnetic changes in the atoms of the brain. These molecular changes are analyzed by a computer to produce a three-dimensional picture of the brain. This picture includes detailed information about brain structures. For example, MRI has been used to show that musicians who play string instruments such as the violin or the cello tend to have an expansion of the brain in an area of the right hemisphere that controls left-hand movement (because control of hands is contralateral, with the right side of the brain controlling the left hand, and vice versa; Münte, Altenmüller, & Jäncke, 2002). We tend to view the brain as controlling what we can do. This study is a good example of how what we do—our experience—can affect the development of the brain. MRI also facilitates the detection of lesions, such as lesions associated with particular disorders of language use, but does not provide much information about physiological processes. However, the two techniques discussed in the following section do provide such information. Metabolic Imaging Metabolic imaging techniques rely on changes that take place within the brain as a result of increased consumption of glucose and oxygen in active areas of the brain. The basic idea is that active areas in the brain consume more glucose and oxygen than do inactive areas during some tasks. An area specifically required by one task ought to be more active during that task than during more generalized processing and thus should require more glucose and oxygen. Scientists attempt to pinpoint specialized areas for a task by using the subtraction method. This method uses two different measurements: one that was taken while the subject was involved in a more general or control activity, and one that was taken when the subject was engaged in the task of interest. The difference between these two measurements equals the additional activation recorded while the subject is engaged in the target task as opposed to the control task. The subtraction method thus involves subtracting activity during the control task from  Page 13 of 16 activity during the task of interest. The resulting difference in activity is analyzed statistically. This analysis determines which areas are responsible for performance of a particular task above and beyond the more general activity. For example, suppose the experimenter wishes to determine which area of the brain is most important for retrieval of word meanings. The experimenter might subtract activity during a task involving reading of words from activity during a task involving the physical recognition of the letters of the words. The difference in activity would be presumed to reflect the additional resources used in retrieval of meaning. Positron Emission Tomography (PET) Scans Positron emission tomography (PET) scans measure increases in oxygen consumption in active brain areas during particular kinds of information processing (O’Leary et al., 2007; Raichle, 1998, 1999). To track their use of oxygen, participants are given a mildly radioactive form of oxygen that emits positrons as it is metabolized (positrons are particles that have roughly the same size and mass as electrons, but that are positively rather than negatively charged). Next, the brain is scanned to detect positrons. A computer analyzes the data to produce images of the physiological functioning of the brain in action. PET scans can assist in the diagnosis of disorders of cognitive decline like Alzheimer’s by searching for abnormalities in the brain (Patterson et al., 2009). PET scans have been used to show that blood flow increases to the occipital lobe of the brain during visual processing (Posner et al., 1988). PET scans also are used for comparatively studying the brains of people who score high versus low on intelligence tests. When high-scoring people are engaged in cognitively demanding tasks, their brains seem to use glucose more efficiently—in highly task-specific areas of the brain. The brains of people with lower scores appear to use glucose more diffusely, across larger regions of the brain (Haier et al., 1992). Likewise, a study has shown that Broca’s area as well as the left anterior temporal area and the cerebellum are involved in the learning of new words (Groenholm et al., 2005). Functional Magnetic Resonance Imaging (fMRI) Functional magnetic resonance imaging (fMRI) is a neuroimaging technique that uses magnetic fields to construct a detailed representation in three dimensions of levels of activity in various parts of the brain at a given moment in time. This technique builds on MRI, but it uses increases in oxygen consumption to construct images of brain activity. The basic idea is the same as in PET scans. However, the fMRI technique does not require the use of radioactive particles. Rather, the participant performs a task while placed inside an MRI machine. This machine typically looks like a tunnel. When someone is wholly or partially inserted in the tunnel, he or she is surrounded by a donut-shaped magnet. Functional MRI creates a magnetic field that induces changes in the particles of oxygen atoms. More active areas draw more oxygenated blood than do less active areas in the brain. So shortly after a brain area has been active, a reduced amount of oxygen should be detectable in this area. This observation forms the basis for fMRI measurements. These measurements then are computer analyzed to provide the most precise information currently available about the physiological functioning of the brain’s activity during task performance. A related procedure is pharmacological MRI (phMRI). The phMRI combines fMRI methods with the study of psychopharmacological agents. These studies examine the influence and role of particular psychopharmacological agents on the brain. They have allowed the examination of the role of agonists (which strengthen responses) and antagonists (which weaken responses) on the same receptor cells. These studies have allowed for the examination of drugs used for treatment. The investigators can predict the responses of patients to neurochemical treatments through examination of the person’s brain makeup. Overall, these methods aid in the understanding of brain areas and the effects of psychopharmacological agents on brain functioning (Baliki et al., 2005; Easton et al., 2007; Honey & Bullmore, 2004; Kalisch et al., 2004).  Page 14 of 16 Another procedure related to fMRI is diffusion tensor imaging (DTI). Diffusion tensor imaging examines the restricted dispersion of water in tissue and, of special interest, in axons. Water in the brain cannot move freely, but rather, its movement is restricted by the axons and their myelin sheaths. DTI measures how far protons have moved in a particular direction within a specific time interval. This technique has been useful in the mapping of the white matter of the brain and in examining neural circuits. Some applications of this technique include examination of traumatic brain injury, schizophrenia, brain maturation, and multiple sclerosis (Ardekani et al., 2003; Beyer, Ranga, & Krishnan, 2002; Ramachandra et al., 2003; Sotak, 2002; Sundgren et al., 2004). Transcranial magnetic stimulation (TMS) A recently developed technique for studying brain activity bypasses some of the problems with other techniques (Walsh & Pascual- Leone, 2005). Transcranial magnetic stimulation (TMS) temporarily disrupts the normal activity of the brain in a limited area. Therefore, it can imitate lesions in the brain or stimulate brain regions. TMS requires placing a coil on a person’s head and then allowing an electrical current to pass through it. The current generates a magnetic field. This field disrupts the small area (usually no more than a cubic centimeter) beneath it. The researcher can then look at cognitive functioning when the particular area is disrupted. This method is restricted to brain regions that lie close to the surface of the head. An advantage to TMS is that it is possible to examine causal relationships with this method because the brain activity in a particular area is disrupted and then its influence on task-performance is observed; most other methods allow the investigator to examine only correlational relationships by the observation of brain function (Gazzaniga, Ivry, & Mangun, 2009). TMS has been used, for example, to produce “virtual lesions” and investigate which areas of the brain are involved when people grasp or reach for an object (Koch & Rothwell, 2009). It is even hypothesized that repeated magnetic impulses (rTMS) can serve as a therapeutic means in the treatment of neuropsychological disorders like depression or anxiety disorders (Pallanti & Bernardi, 2009). Magnetoencephalography (MEG) Magnetoencephalography (MEG) measures activity of the brain from outside the head (similar to EEG) by picking up magnetic fields emitted by changes in brain activity. This technique allows localization of brain signals so that it is possible to know what different parts of the brain are doing at different times. It is one of the most precise measuring methods. MEG is used to help surgeons locate pathological structures in the brain (Baumgartner, 2000). A recent application of MEG involved patients who reported phantom limb pain. In cases of phantom limb pain, a patient reports pain in a body part that has been removed, for example, a missing foot. When certain areas of the brain are stimulated, phantom limb pain is reduced. MEG has been used to examine the changes in brain activity before, during, and after electrical stimulation. These changes in brain activity corresponded with changes in the experience of phantom limb pain (Kringelbach et al., 2007). Brain Disorders A number of brain disorders can impair cognitive functioning. Brain disorders can give us valuable insight into the functioning of the brain. As mentioned above, scientists often write detailed notes about the condition of a patient and analyze the brain of a patient once the patient has died to see which areas in the brain may have caused the symptoms the patient experienced. Furthermore, with the in vivo techniques that have been developed over the past decades, many tests and diagnostic procedures can be executed during the lifetime of a patient to help ease patient symptoms and to gain new insight into how the brain works.  Page 15 of 16 Stroke Vascular disorder is a brain disorder caused by a stroke. Strokes occur when the flow of blood to the brain undergoes a sudden disruption. People who experience stroke typically show marked loss of cognitive functioning. The nature of the loss depends on the area of the brain that is affected by the stroke. There may be paralysis, pain, numbness, a loss of speech, a loss of language comprehension, impairments in thought processes, a loss of movement in parts of the body, or other symptoms. Two kinds of stroke may occur (NINDS stroke information page, 2009). An ischemic stroke usually occurs when a buildup of fatty tissue occurs in blood vessels over a period of years, and a piece of this tissue breaks off and gets lodged in arteries of the brain. Ischemic strokes can be treated by clot-busting drugs. The second kind of stroke, a hemorrhagic stroke, occurs when a blood vessel in the brain suddenly breaks. Blood then spills into surrounding tissue. As the blood spills over, brain cells in the affected areas begin to die. This death is either from the lack of oxygen and nutrients or from the rupture of the vessel and the sudden spilling of blood. The prognosis for stroke victims depends on the type and severity of damage. Symptoms of stroke appear immediately on the occurrence of stroke. Typical symptoms include (NINDS stroke information page, 2009): numbness or weakness in the face, arms, or legs (especially on one side of the body) confusion, difficulty speaking or understanding speech vision disturbances in one or both eyes dizziness, trouble walking, loss of balance or coordination severe headache with no known cause Brain Tumors Brain tumors, also called neoplasms, can affect cognitive functioning in very serious ways. Tumors can occur in either the gray or the white matter of the brain. Tumors of the white matter are more common (Gazzaniga, Ivry, & Mangun, 2009). Two types of brain tumors can occur. Primary brain tumors start in the brain. Most childhood brain tumors are of this type. Secondary brain tumors start as tumors somewhere else in the body, such as in the lungs. Brain tumors can be either benign or malignant. Benign tumors do not contain cancer cells. They typically can be removed and will not grow back. Cells from benign tumors do not invade surrounding cells or spread to other parts of the body. However, if they press against sensitive areas of the brain, they can result in serious cognitive impairments. They also can be life-threatening, unlike benign tumors in most other parts of the body. Malignant brain tumors, unlike benign ones, contain cancer cells. They are more serious and usually threaten the victim’s life. They often grow quickly. They also tend to invade surrounding healthy brain tissue. In rare instances, malignant cells may break away and cause cancer in other parts of the body. Following are the most common symptoms of brain tumors (What you need to know about brain tumors, 2009): headaches (usually worse in the morning) nausea or vomiting changes in speech, vision, or hearing problems balancing or walking changes in mood, personality, or ability to concentrate problems with memory muscle jerking or twitching (seizures or convulsions) numbness or tingling in the arms or legs Head Injuries Head injuries result from many causes, such as a car accident, contact with a hard object, or a bullet wound. Head injuries are of two types. In closed-head injuries, the skull remains intact but there is damage to the brain, typically from the mechanical force of a blow to the head. Slamming one’s head against a windshield in a car accident might result in such an injury. In open-head injuries, the skull does not remain intact but rather is penetrated, for example, by a bullet. Head injuries are surprisingly common. Roughly 1.4 million North Americans suffer such injuries each year. About 50,000 of them die, and 235,000 need to be hospitalized. About 2% of the American population needs long-term assistance in their daily living due to head injuries (What is traumatic brain injury, 2009). Loss of consciousness is a sign that there has been some degree of damage to the brain as a result of the injury. Damage resulting from head injury can include spastic movements, difficulty in swallowing, and slurring of speech, among many other cognitive problems. Immediate symptoms of a head injury include (Signs and symptoms, 2009):  Page 16 of 16 unconsciousness weakness or paralysis abnormal breathing dizziness obvious serious wound or fracture neck pain or stiffness bleeding or clear fluid from the nose, seizure ear, or mouth vomiting more than two to three times disturbance of speech or vision loss of bladder or bowel control pupils of unequal size