Neuropsychological Testing

Neuropsychological testing as practiced by neuropsychologists is an important, perhaps essential adjunct to most neurosurgical practices. Neuropsychology has both clinical and research applications, and over the past century, both have improved the understanding of the neural basis of cognitive and social functions and the effect of brain disorders on these functions. In this chapter, the term clinical neuropsychologist refers to a psychologist with specialization in clinical neuropsychology who has a state license to practice and has been “boarded” in clinical neuropsychology. The term cognitive neuroscientist refers to a psychologist or other research scientist who is interested in the brain basis of cognitive, social, personality, or emotional functions but who does not perform clinical evaluations and is not a licensed practitioner. Neuropsychological testing serves a number of functions ( Table 73.1 ), including assessment of a patient’s cognitive, social-emotional, and sensorimotor abilities with standardized test instruments; quantification of recovery of function after surgery; prediction of performance in real-life circumstances; hypothesis testing about the major functions of a brain sector; ascertainment of outcome variables in treatment trials; determination of the cognitive or social processes (or both) performed by a brain region that is a candidate for surgical excision or modulation; and prediction of quality of life. Such neuropsychological testing can be relatively abbreviated with the use of screening and similar short-duration tests that take less than 1 hour to perform; more typically, such assessment comprises a comprehensive battery of tests to examine most general domains of functioning (e.g., sensorimotor, language, memory, spatial and visual perception, general intellectual ability, executive functions, and personality), which can take between 3 and 6 hours to complete.

Licensed and clinically trained neuropsychologists typically use generally accepted test batteries for their assessment procedures so the test results can be interpreted on the basis of a quantitative summary in comparison with previously acquired normative data that are typical for a rigidly administered, commercially developed battery. Alternatively, a neuropsychologist can make a qualitative judgment of the results from a somewhat idiosyncratic test battery (which usually has a core of tests for which normative data exist). The range of clinically available tests and batteries and an explanation of how to interpret them can be found in many volumes, although a few excellent single-source books are available (e.g., see Lezak and colleagues ). Most patients tested by clinical neuropsychologists demonstrate strengths and weaknesses in a pattern of performance that enables the clinical neuropsychologist to describe the patient’s current abilities and allows a prediction of future functioning.

Cognitive neuroscientists may not be clinically trained, and their scope of practice may be somewhat narrow (e.g., identifying the neural substrates of face recognition), but collaboration with these colleagues, in addition to the clinical neuropsychologist, can often lead to much more detailed information about a type of functional representation within a specific brain region or network, advancing basic brain research. Such information may also have clinical utility if the patient’s lesion falls within that brain region.

Historically, clinical neuropsychological assessment was also used for diagnostic purposes, but with the development of sophisticated imaging, genetic, and related techniques, its contribution to diagnosis is more limited to cases in which imaging may not be helpful, such as the very early stages of a neurodegenerative disease. However, some neuropsychological tests may have a degree of sensitivity to change in performance, so that impairment may be detected early in these patients (e.g., in incipient idiopathic Alzheimer disease or in the very early stages of a tumor). Besides evaluation and diagnosis, a prominent role of neuropsychologists is in the remediation of functional abilities. Such a role includes designing and supervising the administration of training tasks alone or in combination with other forms of intervention (e.g., drugs, noninvasive brain stimulation techniques, or, someday, stem cell therapies) and linking the neuropsychological training techniques to targeted outcomes at work or in the home.

At least one myth about the functions of the cerebral cortex must be debunked. According to conventional wisdom, neurosurgeons needed to avoid language or eloquent brain tissue because postsurgical aphasias could significantly affect recovery and outcome. Conversely, removal of relatively large areas of the anterior frontal lobe, particularly in the right hemisphere, was relatively acceptable. As the functional role of the right frontal lobe has become more apparent since the 1990s, it has become clear that certain outcomes (e.g., employment status and interpersonal functioning in the home) may be more impaired by right frontal lesions that compromise the social, cognitive, and emotional abilities supported by that sector of brain than, for example, naming deficits. Cognitive neuroscientists are playing a major role in revealing the importance of the frontal lobes of the brain, and the ability to specify the functions of the human prefrontal cortex to a level equivalent to the functional assignments of the posterior cortex are forthcoming. Thus the clinical neuropsychologist and cognitive neuroscientist are important team members whose ability to characterize the cognitive, social, and emotional functions of a patient are invaluable to basic research advances and to a neurosurgical practice.