Neuropsychological assessment
1 The practice of neuropsychological assessment
While clinical neuropsychology can trace its lineage directly to clinical neurosciences, psychology
contributed the two other domains of knowledge and skill that are integral to the scientific clinical
practices of neuropsychology today. (1) educational psychologists initially developed tests to capture
the concept ‘intelligence’. (2)the second contribution comes from experimental studies of cognitive
functions in both humans and other animals.
When doing assessments, clinical neuropsychologists typically address a variety of questions of both
neurological and psychological import.
Examination purposes
Any of six different purposes may prompt a neuropsychological examination: diagnosis; patient care;
treatment-1 (identifying treatment needs); treatment-2 (evaluating treatment efficacy); research; and
forensic questions. Many assessments serve two or more purposes.
1. Diagnosis: neuropsychological assessment can be useful for discriminating between
psychiatric and neurological symptoms, identifying a possible neurological disorder in a
nonpsychiatric patient, helping to distinguish between different neurological conditions, and
providing behavioral data for localizing the site - or at least the hemisphere side - of a lesion.
However, today, accurate diagnosis and lesion localization are often achieved by means of the
neurological examination and laboratory data.
Even when the site and extent of a brain lesion have been shown on imaging, the image will
not identify the nature of residual behavioral strengths and the accompanying deficits: for
this, neuropsychological assessment is needed (because every brain is slightly different).
Neuropsychological assessment can aid in prodromal or early detection and prediction of
dementing disorders or outcome. In carriers of Huntington’s disease gene, the earliest
impairments can show up as cognitive deficits identified in neuropsychological assessments,
even before the onset of motor abnormalities.
Screening is another aspect of diagnosis, to identify persons most likely at risk for some
specified condition or in need of further diagnostic study, and where brevity is required.
2. Patient care and planning: many patients are referred for detailed information about their
cognitive status, behavioral alterations, and personality characteristics - often with questions
about their adjustment to their disabilities - so that they and the people responsible for their
well-being may know how the neurological condition has affected their behavior.
Precise descriptive evaluation about cognitive and emotional status is essential for careful
management of many neurological disorders. rational planning usually depends on an
understanding of patients’ capabilities and limitations, the kinds of psychological change they
are undergoing, and the impact of these changes on their experiences of themselves and on
their behavior.
With all the data of a comprehensive neuropsychological examination taken together - the
patient’s history, background, and present situation; the qualitative observations; and the
quantitative scores - the examiner should have a realistic appreciation of how the patient
reacts to deficits and how retraining can best compensate for them, and whether and how
retraining could be profitably undertaken.
Data from successive neuropsychological examinations repeated at regular intervals can
provide reliable indications of whether the underlying neurological condition is changing, and
, if so, how rapidly and in what ways.
Distrust of their experiences, particularly their memory and perceptions, is a problem shared
by many brain damaged persons. The self-doubt of the brain injured person, often referred to
as perplexity, is usually distinguishable from neurotic self-doubt about life goals, values,
principles, etc., but it can be just as painful and emotionally crippling.
The family too, needs to know about their patient’s condition in order to respond
appropriately.
3. Treatment-1: Treatment planning and remediation: in the rehabilitation setting, the
application of neuropsychological knowledge and neuropsychologically based treatment
techniques to individual patients creates additional assessment demands: Sensitive, broad-
gauged, and accurate neuropsychological assessment is necessary for determining the most
appropriate treatment for each rehabilitation candidate with brain dysfunction: problem
areas, strengths and potential for rehabilitation.
4. Treatment-2: Treatment evaluation: neuropsychological evaluation can often best
demonstrate the neurobehavioral response to surgical interventions or to brain stimulation.
Testing for drug efficacy and side effects also requires neuropsychological data.
5. Research: Neuropsychological assessment has been used to study the organization of brain
activity and its translation into behavior, and to investigate specific brain disorders and
behavioral disabilities. Research is also needed for the development of tests.
6. Forensic neuropsychology: Neuropsychological assessment undertaken for legal proceedings
has become quite commonplace in personal injury actions in which monetary compensation
is sought for claims of bodily injury and loss of function. In criminal cases, a
neuropsychologist may assess a defendant when there is reason to suspect that brain
dysfunction contributed to the misbehavior or when there is a question about mental
capacity to stand trial.
The multipurpose examination
Integral to all neuropsychological assessment procedures is an evaluation of the patient’s needs and
circumstances from a psychological perspective that considers quality of life, emotional status, and
potential for social integration.
The validity of neuropsychological assessment
Ecological validity typically refers to how well the neuropsychological assessment data reflect
everyday functioning, or predict future behavior or behavioral outcomes. These questions have been
partially answered, almost always affirmatively. Several components of the prediction of ability to
perform activities of daily living have been explored with neuropsychological assessments, as has
their accuracy for predicting real-world functional disability in neuropsychiatric disorders and
predicting who is ready to drive after neurological injury or illness or at advanced ages.
Scores on an arithmetic test battery were strongly related to those on an ADL questionnaire.
Ross et al. report that two tests (Rey Auditory Verbal Learning Test and Trail Making Test) together
and ‘in conjunction with age significantly predicted psychosocial outcome after TBI as measured by
patient report’. For examining work status after TBI, especially measures of executive functions and
flexibility (Wisconsin Card Sorting Test) are predictive. No measures of trauma severity contributed in
a useful way to the prediction of employment/unemployment. Intact performance on verbal
reasoning, speed of processing, and visuoperceptual measures predicted functional outcome one
year after the TBI event.
,4 The rationale of deficit measurement
One distinguishing characteristic of neuropsychological assessment is its emphasis on the
identification and measurement of psychological - cognitive and behavioral - deficits, for it is in
deficiencies and dysfunctional alterations of cognition, emotionality, and self-direction and
management (i.e. executive functions) that brain disorders are manifested behaviorally.
Neuropsychological assessment is also concerned with the documentation and description of
preserved functions. Yet, brain damage always implies behavioral impairment.
Although the effects of brain disorders are rarely confined to a single behavioral dimension or
functional system, the assessment of psychological deficit has focused on cognitive impairment for a
number of reasons. First, some degree of cognitive impairment accompanies almost all brain
dysfunction and is a diagnostically significant feature of many neurological disorders. Moreover, many
of the common cognitive defects are likely to be noticed by casual observers and to interfere most
obviously with the patient’s capacity to function independently. In addition, psychologists are better
able to measure cognitive activity than any other kind of behavior.
In the following discussion, ‘test’ will refer only to individual tests, not batteries.
Summary scores that are created by averaging individual test scores in a battery may be within some
average range, but deviations between tests can be substantial, even within the typically developing,
healthy population. Accordingly, if one only relies on examining test scores on their deviations
without taking into consideration all of the relevant clinical, historical, and observational data in
evaluating a patient, misclassification can become a considerable problem.
Comparison standards for deficit measurement
The comparison standard may be normative (derived from an appropriate population) or individual
(derived from the patient’s history or present characteristics), depending on the patient, the behavior
being evaluated, and the assessment’s purpose(s).
Normative comparison standards
The population average
The normative comparison standard may be an average or middle (median) score. For many cognitive
functions, variables of age and education or vocational achievement may significantly affect test
performance. These variables are increasingly taken into account in establishing test norms for adults.
In neuropsychological assessment, population norms are most useful in evaluating basic cognitive
functions that develop throughout childhood. Typically, performances of these capacities do not
distribute normally; i.e. the proportions and score ranges of persons receiving scores above and
below the mean are not statistically similar as they are in normal distributions. Functions most suited
to evaluation by population norms also tend to be age-dependent, particularly from the middle adult
years onward, necessitating the use of age-graded norms. Education also contributes to performance
on these tests.
Population norms may be applicable to tests that are relatively pure (and simple) measures of the
function of interest. As the number of different kinds of variables contributing to a measure
increases, the more likely will that measure’s distribution approach normality.
Species-wide performance expectations
The norms for some psychological functions and traits are actually species-wide performance
expectations for adults, although for infants and children they may be age or grade averages. This is
the case for all cognitive functions and skills that follow a common course of development, that are
usually fully developed long before adulthood, and that are taken for granted as part and parcel of
the normal adult behavioral repertory (e.g. speech).
When the behavioral concomitants of brain damage are mild or subtle, particularly when associated
with widespread or diffuse rather than well-defined lesions, few if any of these rudimentary
components of cognitive behavior will be demonstrably impaired on the basis of species-wide norms.
, Customary standards
A number of assumed normative standards have been arbitrarily set, usually by custom. E.g. verbal
response latency - the amount of time a person takes to answer a simple question - which has
normative values of one or two seconds for informal conversation in most Western cultures.
Applications and limitations of normative standards
When it is known or suspected that a patient has suffered a decline in cognitive abilities that are
normally distributed in the adult population, a description of that patient’s functioning in terms of
population norms (i.e. by standard test scores) will, in itself, shed no light on the extent of
impairment unless there was documentation of premorbid cognitive levels (e.g. an average score
would represent a deficit for a person whose premorbid ability level had been generally superior).
The first step in measuring cognitive deficit in an adult is to establish the patient’s premorbid
performance level for all of the functions and abilities being assessed. For those functions with
species-wide norms, this task is easy (adults who can no longer name objects have an obvious
deficit). For normally distributed functions and abilities for which the normative standard is an
average, however, only an individual comparison provides a meaningful basis for assessing deficit.
Individual comparison standards
As a rule, individual comparison standards are called for whenever a psychological trait or function
that is normally distributed in the intact adult population is evaluated for change. When dealing with
functions for which there are species-wide or customary norms, normative standards are appropriate
for deficit measurement.
Knowledge of the rate at which the patient’s performance is deteriorating can contribute to the
accuracy of predictions of the course of a degenerative disease. Also, rate of change studies can give
information about the effectiveness of rehabilitative efforts.
The measurement of deficit
Much of clinical neuropsychological assessment involves intraindividual comparisons of the abilities,
skills, and relevant behaviors under consideration.
Direct measurement of deficit
Deficit can be assessed directly when the behavior in question can be compared against normative
standards. Direct deficit measurement using individual comparison standards can be a simple,
straightforward operation: the examiner compares premorbid and current examples of the behavior
in question and evaluates discrepancies.
Indirect measurement of deficit
In indirect measurement, the examiner compares the present performance with an estimate of the
patient’s original ability level. Historical and observational data are obvious sources of information
from which estimates of premorbid ability may be drawn directly.
The most techniques for indirect assessment of premorbid ability rely on cognitive test scores, on
extrapolation from current reading ability, on demographic variables, or on some combination of
these. The comparison standards for these methods has been the three WIS-A IQ scores or just the
FSIQ (average of all test scores). however, the FSIQ as as a criterion has its problems. E.g. the FSIQ will
necessarily underrepresent the premorbid level of functioning when patients have cognitive
compromise in areas tested by the WIS-A.