NEUROPSYCHOLOGY

Neuropsychology is a scientific field concerned with understanding relationships between the human brain, behavior, and mind, and applying this understanding to the assessment, clinical management, and rehabilitation of persons with neurological disease and injury. Mind includes both conscious (that of which the person is aware) and unconscious (that of which the person is unaware) mental contents and processes, and involves both cognition (e.g., attention, perception, memory, language, thought, mental imagery) and emotion. The history of neuropsychology, within Western culture, is often traced to Hippocrates, who asserted that the brain was the organ of the intellect. Another important historical contribution, occurring at the beginning of the nineteenth century, was that of Franz Josef Gall, who believed that mind could be divided into different functions that are localized within different areas of the brain. During the middle of the nineteenth century, separate reports by physicians Paul Broca, Carl Wernicke, and Hughlings Jackson provided the first clear evidence that the sudden onset of different types of speech and language impairments was associated with damage to different areas within the left hemisphere of the brain. Throughout the twentieth century, the development of neuropsychology was most influenced by scientific discoveries within clinical neurology, psychology (particularly cognitive psychology and theory concerning the mental measurement), and, more recently, neuroscience (including such sub-fields as neuroanatomy, neurophysiology, and neuropharmacology). Contemporary neuropsychology can be divided into two complementary sub-fields: Experimental neuropsychology and clinical neuropsychology.

Experimental neuropsychology

Experimental neuropsychology employs a wide range of scientific methods in an attempt to understand basic brain-behavior-mind relationships. Some of these methods involve the study of non-human animals, observing behavior changes following experimental damage, electrical stimulation, or drug injection within various brain regions, and recording the electrical activity of nerve cells while the animal performs different tasks. In the study of humans, the major method has been the careful measurement of behavioral and mental changes following accidental brain injury, neurosurgery, or the unfortunate occurrence of neurological diseases that affect particular brain regions.

Within the late-twentieth and early-twenty-first centuries, a variety of technologies have been added to the methodology of experimental neuropsychology. Each of these technologies allows a noninvasive (without entering the body) or minimally invasive measurement of brain structure or physiology which can be correlated to measures of behavior, cognition, or emotion during the performance of a specified task. These technologies include: (1) Electroencephalography (EEG; fluctuations in brain electrical activity recorded from sensors placed on the scalp); (2) Event-related potentials (ERP; brain electrical in response to a sensory stimulus or preceding a voluntary movement, recorded from scalp sensors and enhanced by computer averaging); (3) Magnetoencephalography (MEG) recording, from outside the head, of the magnetic field fluctuations generated by nerve-cell activity; (4) computerized tomography (CT), which allows the visualization of brain structure by computer-assisted measures of tissue density calculated by the average absorption of X-rays; (5) magnetic resonance imaging (MRI), which makes a highly detailed visualization of brain structure through computer-assisted measures of cellular composition, calculated from radiowave signal changes following a radio-frequency pulse while the head is within the field of a powerful magnet; (6) functional magnetic resonance imaging (fMRI), which involves the use of MRI technology to visualize changes in blood oxygen content that reflect the metabolic demands of active brain cells; and (7) positron emission tomography (PET), which allows measures of blood flow or metabolic activity of different brain regions, based on emitted subatomic particles from radioactively labeled substances injected into blood vessels that supply the brain.

Overall, the most confident conclusions concerning what brain regions contribute to any particular aspect of behavior, cognition, or emotion are obtained when results from several of these scientific methods converge. As technological developments have allowed increasingly fine-grained measurement of brain structure and processes, a more detailed and sophisticated understanding of human brain-behavior-mind relationships has emerged.

Clinical neuropsychology

Clinical neuropsychology is an applied discipline that uses the basic knowledge from experimental neuropsychologic research to develop reliable and valid procedures for assessing, managing, and rehabilitating persons who suffer from the behavioral, cognitive, and emotional consequences of neurological injury or disease. A variety of different tests of cognitive functions, such as memory, visual and auditory perception, language, and abstract reasoning, have been developed and shown to be sensitive to the consequences of localized brain damage or dys-function. Although not yet as extensively developed, similar tests of emotional functions (e.g., recognition of facial or vocal emotional expression) are available.

In assessing a person with known or suspected neurological injury or disease, the clinical neuropsychologist uses several such tests to draw inferences about the functional integrity of different brain areas and systems. The pattern of strengths and deficits shown by a particular individual on these tests (as judged against performance expectations based on the study of healthy persons of similar age and educational background) can be compared to the documented patterns shown by persons with known neurological injury or disease. The clinical neuropsychologist can thus determine whether the pattern of test scores is consistent with a particular neurological diagnosis.

Neuropsychological testing plays a particularly important role in diagnosis when a given illness (e.g., Alzheimer's disease) manifests primarily by changes in cognition and emotion (rather than in clear physical abnormalities). In addition to diagnosis, neuropsychological assessment plays an important role in giving information to health care providers, patients, and family members concerning specific strengths and deficits in cognitive and emotional functions and their practical implications. Neuropsychological testing is also used in the assessment of treatment effects (e.g., experimental drugs being tested to improve memory in persons with Alzheimer's disease) or disease progression, and in guiding the rehabilitation or clinical management of cognitive, emotional, and behavioral problems.

In selecting, administering, and interpreting neuropsychological tests, several factors need to be considered. First, specific tests should be selected on the basis of whether they meet accepted psychometric criteria. These criteria include demonstrated reliability (consistency of test scores obtained by the same persons when retested with the identical test or an equivalent form) and validity (sensitivity and specificity for the consequences of brain damage or disease). There should also be available normative data (average scores of healthy persons) comparable to the age, educational background, and other characteristics of the person being examined. In addition to test reliability, sensitivity, specificity, and available normative data, the impact of various patient characteristics must be considered. One characteristic known to affect test performance is the individual's age.

Age-related neuropsychological changes

Both age-related sensory acuity changes and response slowing can influence test performance, as can the physical limitations of such prevalent illnesses as arthritis. Changes in visual and auditory acuity with aging are well documented. Such sensory changes can affect neuropsychological test performance by making it more difficult for an older individual to accurately see test stimuli or hear the examiner's instructions. Reaction time shows progressive slowing from early through late adulthood. One obvious implication is that older adults will take longer than younger adults to complete various neuropsychological testing procedures.

Response slowing may also result in lower scores on tests that assign bonus points for faster performance. This underscores the need for age-appropriate normative data to which an individual's performance can be compared. Although healthy older people are unlikely to fatigue more rapidly than younger adults during average-length (e.g., two to three hours) testing sessions, older persons in poor health are likely to fatigue quickly. It may thus be necessary to take more frequent breaks during a neuropsychological examination session when evaluating older (particularly ill or frail) adults. Performance limitations imposed by physical disabilities (e.g., arthritis) may require modifications in testing procedures (e.g., allowing the person to work on a task beyond the standard time limits). Such departures from standardized test procedures require both caution and clinical experience when interpreting performance.

Even on neuropsychological tests that do not assign bonus points for faster performance, and for which age-related sensory changes do not likely contribute, performance is often poorer for older adults than for younger adults. This is particularly true for tests of memory and for tests of abstract reasoning and complex problem solving. There is both animal and human experimental data that suggests age-associated memory changes are due to cell loss and physiologic changes within the hippocampal complex, a deep brain region known to be important for establishing longer-lasting memories. Similarly, human experimental neuropsychological data has indicated that age-associated decreases in abstract reasoning and complex problem-solving ability likely reflect cellular and physiologic changes within the frontal lobes and deep brain structures to which they are interconnected. The frontal lobes and their interconnected brain structures are known to be important for a range of complex cognitive abilities that have been collectively termed executive functions.

However, it should be noted that there is greater variability in neuropsychological test performance among older (versus younger) individuals, with some older adults performing within the range of average younger persons. This observation has led to controversy over whether age-group differences in neuropsychological test performance should be thought of as reflecting necessary changes in brain structure and functioning with aging or as the manifestation of subtle age-associated neurological disease processes within a subgroup of older adults. The resolution of this controversy must await future research, particularly that employing longitudinal research designs in which persons are repeatedly examined (both neuropsychologically and with sophisticated brain imaging technologies) as they age.

Neuropsychological diagnosis of dementias

Dementia is the term used to describe a clinical syndrome of progressive impairment of cognitive functions, often with accompanying changes in behavior and emotion. Many different illnesses can cause the syndrome of dementia. Accurate diagnosis of the particular illness that is likely causing dementia (e.g., Alzheimer's disease, Huntington's disease, Parkinson's disease, fronto-temporal dementia), requires the efforts of a multidisciplinary team of physicians (particularly neurologists and psychiatrists), neuropsychologists, and other health professionals (e.g., social workers). Neuropsychological assessment plays an important role in the clinical identification of the dementia syndrome and the differentiation of various dementia-causing illnesses.

Brief mental status questionnaires can provide health professionals with a quick documentation of the presence of dementia. However, such questionnaires are generally not sufficiently sensitive to detect very mild dementia, particularly in persons who had high intellectual functioning before the onset of their illness. This is due to mental status questionnaires being composed of fairly easy questions. Mental status questionnaires also lack the specificity to assist in differential diagnosis of dementia types, due to the fact that, typically, too few cognitive functions are assessed. In comparison, standardized neuropsychological tests contain a range of task difficulty. This provides for greater sensitivity to subtle or mild cognitive impairment than what is possible through the use of mental status questionnaires.

The ability of neuropsychological test batteries to examine the pattern of performance across different, reliably measured areas of cognitive functioning helps to differentiate dementias caused by particular illnesses. Different dementia-causing illnesses do not manifest with equivalent impairment across all areas of cognitive function. Thus, inspection of the pattern of performance across various neuropsychological tests can be used as an aid to diagnosis. For example, research has demonstrated that Alzheimer's disease typically begins with changes in memory ability that accompany neuronal damage within the hippocampal complex. Neuropsychological tests that assess recall of novel information after a short delay have been shown to be sensitive to these early memory changes. In contrast, regions of the frontal and temporal lobes of the brain are often first affected by the fronto-temporal dementias. Tests of executive functions, including abstract reasoning, problem solving, and the ability to easily shift mental set (readiness to respond in a given manner to a stimulus), are thus most sensitive to the early cognitive changes of fronto-temporal dementia.

It can be difficult to clinically differentiate the early changes of Alzheimer's disease or other dementias from the cognitive impairment that can accompany depression in older adults. Older persons with depression may show deficits on a range of neuropsychological tests, particularly on tests requiring sustained attention or rapid performance, and on tests with pleasant or neutral (in contrast with unpleasant) content. The term pseudodementia was once used to describe persons with depression and cognitive impairment, reflecting the expectation that the cognitive deficits would reverse with effective treatment of the depression. This term is no longer in use because research has shown that many of these persons show a progressive dementia that does not reverse with depression treatment. Such studies have indicated the need for both caution and reassessment in attempts to differentiate cognitive deficits associated with depression from those due to Alzheimer's disease or other dementias.

Alfred W. Kaszniak

See also Alzheimer's Disease; Dementia; Mental Status Examination; Psychological Assessment; Reaction Time.

BIBLIOGRAPHY

Bondi, M. W.; Salmon, D. P.; and Kaszniak, A. W. "The Neuropsychology of Dementia." In Neuropsychological Assessment of Neuropsychiatric Disorders, 2d ed.. Edited by I. Grant and K. H. Adams. New York: Oxford University Press, 1996. Pages 164–199.

Duke, L. M., and Kaszniak, A. W. "Executive Control Functions in Degenerative Dementias: A Comparative Review." Neuropsychology Review 10 (2000): 75–99.

Green, J. Neuropsychological Evaluation of the Older Adult: A Clinician's Guidebook. San Diego: Academic Press, 2000.

Kaszniak, A. W. "Techniques and Instruments for Assessment of the Elderly." In A Guide to Psychotherapy and Aging. Edited by S. H. Zarit and B. G. Knight. Washington, D.C.: American Psychological Association, 1996. Pages 163–219.

Kaszniak, A. W., and NEWMAN, M. C. "Toward a Neuropsychology of Cognitive Aging." In Psychology and the Aging Revolution: How We Adapt to Longer Life. Edited by S. H. Qualls and N. Abeles. Washington, D.C.: American Psychological Association, 2000. Pages 43–67.

Kolb, B., and Whishaw, I. Q. Fundamentals of Human Neuropsychology, 4th ed. New York: W. H. Freeman and Company, 1996.

Nussbaum, P. D., ed. Handbook of Neuropsychology and Aging. New York: Plenum, 1997.

Tuokko, H., and Hadjistavropoulos, T. An Assessment Guide to Geriatric Neuropsychology. Mahwah, N.J.: Lawrence Erlbaum Associates, 1998.

Neuropsychology

Neuropsychology is the area of neuroscience that studies relationships between brain function and behavior, with a central focus on human brain-behavior relationships. Neuropsychological research attempts to map the brain structures and functions that are critical for particular mental/cognitive, emotional, and behavioral capacities. Clinical neuropsychology involves assessment of persons with diseased or damaged brains to evaluate whether the patient's cognitive, behavioral, or emotional functioning has been compromised. Developmental neuropsychology is the study of the relationship between the development of brain structure and function, and the emergence of cognitive abilities. Finally, neuropsychological rehabilitation attempts to ameliorate the negative impact of brain damage.

See also Mind-brain Interaction; Neurosciences

warren s. brown