An Introduction to Neuropsychological Assessment
by Alan E. Brooker
Clinical neuropsychology is a specialized field of endeavor which seeks
to apply the knowledge of human brain-behavior relationships to clinical
problems. Human brain-behavior relationships refer to the study of
research-derived associations between an individual's behavior, both
normal and abnormal, and the functioning of his or her brain. The clinical
neuropsychologist takes extensive measurements of a variety of kinds of
human behavior, including receptive and expressive language,
problem-solving skills, reasoning and conceptualization abilities,
learning, memory, perceptual-motor skills, etc. From this complex and
detailed set of behavioral measurements, a variety of inferences can be
drawn relating directly to the functioning of an individual's brain. In
clinical neuropsychology, the operation and condition of an individual's
brain is assessed by taking measures of his or her intellectual, emotional
and sensory-motor functioning.
In studying brain functioning by measuring behavior, the clinical
neuropsychologist makes use of a specialized set of tools which is
appropriately labeled the clinical neuropsychological evaluation. This
instrument is generally composed of numerous psychological and
neuropsychological procedures which measure various abilities and skills.
Some of these procedures are drawn from psychology (WAIS-R, Form Board in
TPT) and others have been developed specifically from neuropsychological
research (Category Test, Speech Sounds Perception Test, etc.). These
strictly neuropsychological procedures compose the greater part of the
evaluation, especially since they were developed specifically to assess
brain functioning by measuring higher mental abilities. Still other
procedures in the evaluation were borrowed directly from neurology
(certain items on Aphasia Screening; Sensory Perceptual Examination) and
were standardized in their administration. Some of the procedures in the
evaluation are rather homogeneous in that they depend on mainly one
ability or skill for success or failure (Finger Oscillation Test primarily
relies on motor tapping speed). Other procedures are more heterogeneous
and depend on the organized and complex interaction of several distinct
skills or abilities for success (Tactual Performance Test - tactile
perceptual ability; appreciation of two-dimensional space; planning and
sequencing ability; etc.). In all, the clinical neuropsychological
evaluation gives the practitioner in this field a wealth of information
about an individual's unique pattern of skills and abilities.
The clinical neuropsychological evaluation has essentially two main
purposes: one involving diagnosis and the other involving behavioral
description. The diagnostic power of a neuropsychological instrument, such
as the Halstead-Reitan Battery, has been well documented and need not be
discussed in detail (Vega and Parsons, 1967; Filskov and Goldstein, 1974;
Reitan and Davison, 1974). In neuropsychological diagnosis, the presence
or absence of impairments in brain functioning can be determined along
with other important factors, such as lateralization, localization,
severity, acuteness, chronicity or progressivity, and type of impairment
suspected of being present (tumor, stroke, closed head injury, etc.). Four
primary methods of inference are utilized in making these determinations,
namely, level of performance, pathognomonic sign, comparison of the two
sides of the body and specific patterns of test scores.
The level of performance approach primarily involves determining how
well or how poorly an individual performs on a certain task, usually by
means of a numerical score. Cut-off scores are generally developed for
such a task, which allow the practitioner to classify an individual as
either impaired or unimpaired with respect to brain functioning, depending
upon whether his score falls above or below the cut-off value in use. The
Halstead Category Test provides an example of this level of performance
approach. On this procedure, a score of 51 errors or above places an
individual in the impaired range. Likewise, a score of 50 errors or below
places the individual in the normal range generally characteristic of
individuals with unimpaired brain functioning. The primary danger of using
level of performance measures alone to diagnose brain dysfunction is that
of classification errors. In most cases, the cut-off score will not
completely separate individuals with brain dysfunction from those without.
Therefore, both false-positive and false-negative errors can be expected,
depending upon the particular cut-off score established. Such a procedure
in fact used in isolation is tantamount to employing single tests to
diagnose "brain damage," and this approach has been justly criticized
in previous work (Reitan and Davison, 1974). Additional methods of
inference are used in neuropsychological assessment in order to sharpen
diagnosis and minimize errors.
The pathognomonic sign approach essentially involves identifying
certain signs (or specific types of deficient performance) which are
always associated with brain dysfunction whenever they occur. An example
of such a pathognomonic sign would be an instance of dysnomia on Aphasia
Screening made by an individual with a college degree and normal IQ
values. Such an individual would not be expected to say "spoon"
when shown a picture of a fork and asked to name this object. The
appearance of a true pathognomonic sign in a neuropsychological evaluation
can always be associated with some sort of impairment in brain
functioning. However, the converse is not true. That is, the absence of
various pathognomonic signs in a particular individual's record does not
mean that this individual is free of brain dysfunction. Thus, using the
pathognomonic sign approach alone, one runs a considerable risk of making
a false-negative error or discounting the presence of brain dysfunction
when it in fact does exist. If other methods of inference are employed
with this approach, however, then the likelihood is increased that any
brain dysfunction present will be identified even in the absence of
pathognomonic signs. Therefore, one may again see the value of and
necessity for multiple and complimentary methods of inference in clinical
neuropsychology.
The third method of inference involves a comparison of the performances
of the two sides of the body. This method was borrowed in principle almost
directly from clinical neurology but involves measurement of a variety of
sensory, motor and perceptual-motor performances on the two sides of the
body and comparing these measures with respect to their relative
efficiency. Since each cerebral hemisphere governs (more or less) the
contralateral side of the body, some idea of the functional condition of
each hemisphere relative to the other can be gleaned from measuring the
performance efficiency of each side of the body. An example here is the
Finger Oscillation Test. Here, tapping speed in the dominant hand is
compared with tapping speed in the non-dominant hand. If certain expected
relationships are not obtained, then inferences with respect to the
functional efficiency of one hemisphere or the other can be made. This
inferential approach provides important corroborative and complementary
information, especially with respect to lateralization and localization of
brain dysfunction.
The final, method of inference to be discussed is that of specific
patterns of performance. Certain scores and results may combine into
particular patterns of performance which carry important inferential
meaning for the clinician. For example, the relative absence of
constructional dyspraxia, sensory-perceptual deficits, and aphasic
disturbances, together with significant deficits on grip - strength,
Finger Oscillation and the Tactual Performance Test, may possibly be
associated with brain dysfunction which is more anterior in location than
posterior. As another example, severe constructional dyspraxia with an
absence of aphasic disturbances, together with severe sensory and motor
losses in the left upper extremity, is likely associated with dysfunction
in the right hemisphere rather than in the left.
Clinical neuropsychological diagnosis of brain dysfunction is carried
out utilizing four primary methods of inference in a complex yet
integrated fashion. Each of these methods is dependent upon and
complementary to the others. The strength of neuropsychological diagnosis
lies in the simultaneous utilization of these four methods of inference.
Thus, some particular impairment in brain functioning may yield relatively
normal levels of performance but, at the same time, may produce certain
pathognomonic signs or yield patterns of performance which are clearly
associated with brain dysfunction. The cross-checks and multiple avenues
of gaining information, made possible by the simultaneous use of these
four methods of inference, allow sound and accurate diagnosis of brain
dysfunction by the experienced clinical neuropsychologist.
The second major purpose of clinical neuropsychology, as mentioned
above, is behavioral description and delineation of behavioral strengths
and weaknesses. This type of formulation can be most essential in making
recommendations for an individual's treatment, disposition and management.
This, in fact, is considered by some practitioners to be the most
important function of the clinical neuropsychological evaluation.
Behavioral description is the clinical neuropsychologist's unique input
into a patient's total medical workup. Other specialists, notably the
neurologist and neurosurgeon, are excellent neurological diagnosticians,
and it is not the purpose of clinical neuropsychology to compete with
these individuals or attempt to take their place. Thus, neuropsychological
diagnosis can be considered an additional avenue of diagnostic input into
a patient's workup.
Behavioral description, on the other hand, is the clinical
neuropsychologist's unique domain. Here, this practitioner can provide
input into a patient's total medical picture which is not available from
any other source.
Behavioral descriptions should start out with a thorough understanding
of the patient's background, his educational level, his occupation, his
age, his likes, dislikes, future plans, etc. This information is usually
brought into play subsequent to a blind analysis of the patient's
neuropsychological evaluation and a preliminary diagnosis and behavioral
description based on this analysis. Before the final behavioral
description and recommendations are given, however, the patient's
background information is integrated into the formulation. Here, the
clinical neuropsychologist can look at the particular patient's pattern of
intellectual and adaptive strengths and weaknesses shown on the
neuropsychological evaluation and integrate these findings with the
patient's individual situation. This can be considered to be a very
important process in terms of formulating specific, meaningful and
directly applicable recommendations for the particular individual under
study.
Specific issues which often warrant coverage in neuropsychological
behavior description involve a variety of areas. From the clinical
neuropsychological evaluation, specific areas in need of rehabilitation
can be identified, as well as areas of behavioral strength which warrant
the individual's awareness. Advice on coping with environmental demands in
the face of particular behavioral deficits is often necessary, as well as
some realistic prediction of future change in neuropsychological status.
The degree of behavioral deficit in various areas can often be specified
and questions with respect to a patient's ability to manage himself and
behave adaptively in society can be answered directly. Forensic issues can
often be dealt with in terms of providing direct, clear information with
respect to a patient's judgment, competence, degree of intellectual and
adaptive loss following brain disease or trauma, etc. Other specific areas
in which the clinical neuropsychological evaluation can provide input
include educational potential, occupational potential, the effects of
brain dysfunction on social adjustment, etc. The importance of the
behavioral picture of a patient obtained from the neuropsychological
evaluation is immense.
As mentioned above, the clinical neuropsychological evaluation is not
meant to compete with or take the place of more traditional medical
procedures. In fact, certain important differences exist between the
clinical neuropsychological evaluation and these procedures. First of all,
the neuropsychological evaluation is primarily concerned with higher
mental abilities, such as language, reasoning, judgment, etc. Traditional
neurology, on the other hand, emphasizes assessment of sensory and motor
functions and reflexes. Thus, although the neurologist and
neuropsychologist study the same general phenomenon, that is, nervous
system function and dysfunction, these practitioners nevertheless
emphasize different aspects of this phenomenon. The clinical
neuropsychologist takes precise and specific measurements of a variety of
aspects of higher cortical functioning. The neurologist, on the other
hand, primarily concentrates on lower-level phenomena of nervous system
functioning. The results of these two types of evaluation may not always
agree, given the different aspects of the central nervous system
emphasized and the different methods and procedures used by each of these
practitioners. Logically, the clinical neuropsychological assessment and
the neurological evaluation should be considered complementary to each
other. Certainly, neither one is a substitute for the other. Where
possible, both of these procedures should be employed in order to obtain a
full and detailed picture of an individual's central nervous system
functioning.
Traditional psychological assessment procedures and the clinical
neuropsychological evaluation also have a number of differences worth
noting. In traditional psychological assessment, for example, an
individual's average or modal performance is usually desired. On the
neuropsychological evaluation, however, the examiner strives to obtain an
individual's best or optimal performance. Considerable encouragement and
positive support is given to the patient during a neuropsychological
evaluation to perform as well as possible. Such encouragement is generally
not given under traditional psychological assessment conditions.
Additionally, psychological procedures, such as the Rorschach, MMPI,
Wechsler Intelligence Scales, Draw-A-Person, etc., have traditionally been
used by psychologists who diagnose brain damage and disease. Although each
of these procedures may contribute significant information about a
person's behavior, their validity in detecting the presence or absence of
brain dysfunction and determining the nature and location of the
dysfunction is rather limited. These assessment procedures have not been
developed specifically for the purpose of identifying and describing brain
damage and disease. The clinical neuropsychological evaluation, on the
other hand, has been developed specifically for this purpose and has been
validated against stringent medical criteria, such as surgical findings
and autopsy reports. In addition, traditional psychological assessment
procedures generally do not make use of the multiple inferential methods
employed by the clinical neuropsychological evaluation. Oftentimes, only
one or at most two inferential methods are used with traditional
psychological assessment procedures in making determinations of the
presence or absence of brain dysfunction. Thus, the comprehensive approach
to making inferences and drawing conclusions used by the clinical
neuropsychologist is felt to be superior to more traditional psychological
methods in the diagnosis and description of brain dysfunction.
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References
Filskov, S. & Goldstein, S. (1974). Diagnostic
validity of the Halstead-Reitan Neuropsychological Battery. Journal of
Consulting and Clinical Psychology, 42(3), 382-388.
Lezak, M.D. (1983). Neuropsychological Assessment.
New York: Oxford University Press.
Reitan, R.M. & Davidson, L..A. (1974). Clinical
Neuropsychology: Current Status and Applications. Washington: VJ-I.
Winston & Sons.
Vega, A., & Parsons, 0. (1967). Cross-validation of
the Halstead-Reitan Tests for brain damage. Journal of Consulting
Psychology, 31(6), 619-625.
About the author - Dr. Alan E. Brooker is a
clinical neuropsychologist with the Department of Mental Health at the
David Grant USAF Medical Center. Travis Air Force Base, CA. 94535.
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