I. Foundations of Neuropsychology

CHAPTER 19 Neuropsychology

OUTLINE I. FOUNDATIONS OF NEUROPSYCHOLOGY Neuropsychology is the study of the relationships among brain processes, human behavior, and psychological functioning. It rests on two assumptions: (1) Complicated mental tasks can be tested and studied separately and (2) Different psychological processes are controlled by different regions (or combinations of regions) in the brain. Experimental neuropsychologists study primarily people with brain damage to understand brain function better, while clinical neuropsychologists use this knowledge to help treat individuals with brain damage or dysfunction. A. A Brief History of Neuropsychology Localization of function is the idea th specific psychological functions can be affected by damage to a specific brain area. In the early 1800s, this was not a commonly accepted notion. Franz Gall proposed it but had also mistakenly believed in a variety of other ideas about brain science that turned out to be false (including phrenology). Later, Paul Broca, who had higher status in the scientific community, found that certain speech difficulties were related to brain lesions in a specific locations. This finding ultimately led to the acceptance, and broader support, of the notion of localization of function. B. Modules and Networks Modules are discrete brain regions that perform their own kinds of unique analysis. Somewhat like a circuit board, each module adds a required piece of the puzzle that allows speech, or some other complex function, to occur. Teams of modules form networks, which are collectively responsible for more global functions. C. Lesion Analysis Lesion analysis is the study of localization of function by looking at the results of brain damage. To do this, experimental neuropsychologists must know what precise ability, or psychological function, has been damaged. Such assessments are made through neuropsychological testing. D. Neuropsychological Testing Neuropsychological testing can either be individually tailored or involve a standardized test battery. Standardized batteries have the advantage of giving the same test in the same way to all patients, but they are unable to be tailored to a particular patient’s problem. Most clinical neuropsychologists start with a standardized test battery and then follow up with individual tests that look relevant. To interpret test results, neuropsychologists rely on norms to reveal if a particular result is abnormal or normal. E. Training for Neuropsychology Training in neuropsychology focuses on learning about a large number of different neuropsychological tests, including how to give and score them and interpret results. Usually, training involves earning a Ph.D. in clinical psychology with a focus on neuropsychology, followed by an internship under the supervision of a licensed clinical neuropsychologist. Clinical neuropsychologists are employed by hospitals or specialty clinics. Experimental neuropsychologists are usually employed in a university setting where they teach, conduct research, and test patients as time permits. II. MECHANISMS OF BRAIN DYSFUNCTION A. Stroke Disruption of behavior and mental processes due to loss of blood supply in some part of the brain is known as a stroke. How disabling a stroke is depends on the location of the damage more than the size of the stroke. Pain is usually not associated with stroke, which means the victim may not recognize the problem. This can delay medical treatment, which is problematic as speed of treatment is one of the significant determinants of recovery. Other factors that affect recovery following a stroke include the quality of the medical treatment, the size and location of the stroke, the health of the remaining blood vessels and brain tissue, and the nature of the rehabilitation program. B. Trauma Trauma is damage to the brain due to sudden impact. This impact may involve an object striking the head, or the head suddenly stopping or starting movement. It occurs because the brain floats in cerebrospinal fluid, and as an object strikes the head or the abrupt head movement occurs, the brain slides around in its bony case. As it bumps and bounces against bone, nerve fibers are damaged. The amount of damage depends on the degree of force, and damage in trauma tends to be more widespread compared to strokes. C. Neurodegeneration Neurodegeneration is the gradual process of cell damage in the brain. Notable examples include Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. Each of these diseases affects a particular kind of brain cell (or cells in a particular location), causing specific loss of function. Causes of neurodegeneration are largely unknown, although infection, nutritional deficiency, and genetic abnormalities have been known to cause it. III. NEUROPSYCHOLOGICAL DISORDERS Patterns of symptoms typically observed in individuals with stroke, trauma, or neurodegeneration are known as neurological disorders. A. Amnestic Disorders Amnestic disorders involve memory loss. Examples include anterograde amnesia and Korsakoff’s syndrome. Anterograde amnesia involves damage to the hippocampus and results in inability to form new memories. Korsakoff’s syndrome can be caused by vitamin B1 deficiency or by alcoholism resulting in damage to the medial dorsal thalamus. Such damage yields anterograde amnesia with confabulation, the creation of false memories. B. Disorders of Consciousness Disorders of consciousness involve impairment of the ability to accurately be aware of the world. For example, damage to the reticular activating system (RAS) can result in a coma (severe damage) or a persistent vegetative state (lesser damage). Chances of recovery are low for such disorders. Damage to both sides of the cortex can also result in disorders of consciousness. Delirium, the waxing and waning of consciousness, can be caused by fever, poisoning, or infection. It is usually not permanent. Anosognosia, the absence of the knowledge of disease, is possible when damage occurs to the right side of the brain. C. Thinking Critically: Can Someone Be Partially Paralyzed and Not Know It? What am I being asked to believe or accept? That patients with hemiparesis (paralysis on one side of the body) are genuinely unaware of their partial paralysis. What evidence is available to support the assertion? Hemiparesis patients seem aware of other areas of weakness and potentially upsetting occurrences, which is unlikely if they were simply using ego defense mechanisms to avoid coping with the hemiparesis. Furthermore, hemiparesis is more likely with right hemisphere brain damage than left—unlikely if ego defenses are the underlying explanation for the lack of awareness. Finally, using the Wada technique, scientists have demonstrated that hemiparesis patients show anosognosia even when the paralysis is known to be temporary. Together, these finding suggest that hemiparesis patients are not using ego defenses to avoid awareness of their paralysis but indeed are genuinely unaware of their condition. Are there alternative ways of interpreting the evidence? One problem with the Wada technique is that it is retrospective—it requires patients to describe their experience while “paralyzed” after the fact. Recalled answers may differ from those that might be given while actually under paralysis. Family studies suggest that individuals who tended to use denial as a coping mechanism before their hemiparesis occurred were most likely to experience anosagnosia as compared to those individuals who tended to not use denial as a coping tool. What additional evidence would help to evaluate the alternatives? Retrospective bias makes the interpretation of the Wada technique results and the family studies difficult. One solution would be to conduct a prospective study in which individuals were identified and their stress-coping techniques assessed. They could then be followed for a period of time to determine whether those individuals who used denial most consistently were more likely to experience anosagnosia following a stroke. What conclusions are most reasonable? Until prospective studies have been conducted, it is most reasonable to conclude that at least some of the anosagnosia that occurs with hemiparesis is indeed genuine unawareness. D. Disorders of Perception Damage to perceptual systems in the brain causes disorders of perception. In the visual system, such damage can occur in the “what” and in the “where” neural pathways. “What” neural pathways, so named because they help us determine what we are seeing, are in the cortical region leading to the ventrolateral temporal lobe. Damage to the “what” systems can result in visual agnosia, a condition in which one is unable to identify objects. “Where” neural paths are the cortical regions leading to the parietal lobe. Damage to these paths can yield simultanagnosia (difficulty perceiving a whole scene) or hemineglect (difficulty responding to information from one side of the world). E. Focus on Research Methods: Studying Hemineglect It is difficult to know if hemineglect is a perceptual problem or a sensory problem, because one can’t report on a perception unless it originated with a sensation. Bisiach proposed that if it is perceptual, then the neglect of a side of the world will occur in imagination as well as raw sensations. To test this idea, he created stimuli and presented them to participants with hemineglect through a “slit” so that the participants had to imagine the whole. Even in these imagined representations, participants displayed hemineglect. However, these patients all had damage in the parietal lobes, so damage in other parts of the brain need to be studied as well. F. Linkages: Language Disorders and the Brain Damage to the brain that results in difficulty speaking, reading, writing, and understanding language is known as a language disorder, or aphasia. Most aphasias result from damage to the left side of the brain. Broca’s aphasia is the loss of the ability to produce language fluently. Wernicke’s aphasia is difficulty understanding language and sensations more generally. Aprosodia is the inability to use tone to communicate meaning or to understand the meaning of what someone else is saying. G. Disorders of Movement When learned motor skills are disrupted due to brain damage or dysfunction, one is said to have a disorder of movement, or apraxia. Ideational apraxia occurs when movements are performed correctly but in the wrong sequence. Ideomotor apraxia occurs when the sequence of movements is correct but the performance of skilled movements is poor. H. Dementia Dementia is diagnosed when a person has notable impairment of memory along with at least one other impairment of psychological function, and the impairments have significant impact on daily living requirements. It is usually caused by a progressive neurodegenerative brain disorder, such as Alzheimer’s disease. Alzheimer’s disease affects the brain mainly through neurons that use the neurotransmitter acetylcholine, including cells in the hippocampus. Thus, one of the main symptoms of Alzheimer’s disease is difficulty forming new memories. In contrast, vascular dementia is caused by restrictions in blood supply to the brain, while the hippocampus is relatively well-preserved. Patients with vascular dementia can form new memories but have difficulty retrieving them.