Conceptual Issues In Pediatric Neuropsychological Assessment

Neuropsychological assessment of a pediatric population differs in a number of respects from such assessment of an adult population. Whereas a primary feature of adult neuropsychological assessment is that it is based on the loss or impairment of a previously acquired function, child neuropsychological assessment is concerned with a comparable function that may be slowed in development, limited in its extent of development, or totally precluded from development. A critical feature in this respect involves the age at which insult to the central nervous system is sustained and, to a lesser but interactive extent, the brain area or functional system sustaining insult. For more than 100 years it has been documented that, in an adult, damage to a specific brain area (i.e., in the dominant cerebral hemisphere foot of third frontal convolution) may produce loss of the ability to speak (i.e., Broca's type aphasia). However, damage to the same area in a very young child may produce no apparent problems in the development of expressive speech due to the recruitment of intact areas of the nondominant cerebral hemisphere to subserve this function. Neuropsycho-logical assessment of such children, however, may reveal impairment of the functions typically subserved by cortical areas that have been recruited to accommodate the mechanisms of expressive speech. Interestingly, there appears to be an upper age level, somewhere around 8 years of age, after when such contralateral recruitment no longer occurs or occurs to a substantially attenuated extent.

Obviously the diagnosis of an ability (e.g., expressive speech) that has been acquired and then lost is much easier than that of the impaired emergence or slowed rate of development of a skill not within the individual's prior repertoire. Accordingly, neuropsy-chological assessment of pediatric age populations requires considerable knowledge of the expected ages at which neurodevelopmental phenomena affecting cognitive and behavioral adjustment may be expected to occur, as well as the normal sequence of stages through which such development occurs.

This age specificity constitutes perhaps the most important difference between neuropsychological assessment in pediatric as opposed to adult populations. In the adult population the span of a decade—say between 30 and 40 years of age—produces relatively little change in neurological maturation or organization, and level of performance on most diagnostic measures can, for the most part, be interpreted in the same way for a younger vs an older individual in this age range, with little differentiation between genders except on measures of strength. Conversely, the difference in neuropsychological repertoire between a 2 year-old and a 7-year-old is at once remarkable and striking, reflecting the phenomenal changes in neurological organization occurring during this 5-year period. Accordingly, pediatric neuropsychological assessment needs to consider and take into account the emerging states of central nervous system structures and functions subserving given abilities measured by assessment and be prepared to incorporate such considerations into a diagnostic profile.

In a typical 2-year-old, receptive language is usually reflected in the ability to recognize a few words of command and to match pictures of a few familiar objects to the spoken word (e.g., cat, cup, chair) associated with such objects. By age 7 years, brain maturation has occurred to an extent sufficient to permit the recognition of abstract symbols representing letters of the alphabet and words composed of such symbols. Conceptually, this age may also include understanding of bigger-smaller, pretty-ugly, and alike-different at varying levels generally corresponding to younger vs earlier stages of this 5-year range. Obviously, pediatric neuropsychological assessment needs to be based on an understanding and appreciation of such development to permit understanding of whether a given child's performance on given tests suggests dysfunction in the central nervous system. An example of the interaction between developmental level and specific neurocognitive function may help to provide an illustration of the interdependence of development and central nervous system, normally vs abnormally.

Consider a specific function mediated by the central nervous system, expressive language. Expressive language at a 5-year-old level in an 8-year-old child of normal intellectual ability may be indicative of brain dysfunction involving frontal areas of the dominant cerebral hemisphere, whereas such expressive language functions in an 8-year-old of borderline intellectual ability may represent nothing more remarkable than a manifestation of intellectual function.

More complex functions mediated by the central nervous system in children are encountered with considerably greater frequency than single problems such as expressive language, which may ultimately depend on a single location in the brain (i.e., foot of the second frontal convolution). A diagnostic question frequently presenting for pediatric neuropsychological assessment involves that of reading difficulty. Obviously, before the possible central nervous system components of such a problem can be assessed, the pediatric neuropsychologist must rule out or at least consider the potential effects of such factors as poor educational instruction, mismatch between educational instructional procedure and the child's learning style, possible language barriers, sensory problems involving sight or hearing, impaired motivation, genetic factors, emotional problems, or health factors including medication use that might be operative. Next, the evaluation of the child's reading problem needs to proceed along anatomical parameters. Is there a specific word blindness that might implicate brain areas in the supramarginal-angular gyrus area of the dominant cerebral hemisphere? Does the problem involve associational deficits corresponding with frontal lobe functions? Can the child actually perceive and recognize words but have difficulty translating this into an appropriate response? Is there dysfunction among functions mediated by the arcuate fasciculus?

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