CHAPTER 16 Neuropsychological Testing
Neuropsychological testing as practiced by neuropsychologists is an important, some might say necessary, adjunct to most neurosurgical practices. Neuropsychology has both a clinical and research arm, and over the past century both have been productive in helping humanity achieve a better understanding of the neural basis of cognitive and social functions and the impact of brain disorders on these functions. In this brief chapter I use the term clinical neuropsychologist to refer to a psychologist with specialization in clinical neuropsychology who has a state license to practice and has been “boarded” in clinical neuropsychology. I use the term cognitive neuroscientist to refer 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 (e.g., see Table 16-1), including assessment of the cognitive, social-emotional, and sensorimotor abilities of a patient 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 an hour to perform or, more typically, be composed of a comprehensive battery of tests to examine most general domains of functioning (e.g., sensorimotor, language, memory, space and visual perception, general intellectual ability, executive functions, and personality), which can take between 3 and 7 hours to complete.
TYPE OF NEUROPSYCHOLOGICAL INPUT | PRACTITIONER | GOAL |
---|---|---|
Broad-based or targeted neuropsychological evaluation | Clinical neuropsychologist | Characterization of the patient’s cognition, social skills, personality, and mood. Prediction of outcome |
Repeated neuropsychological evaluations | Clinical neuropsychologist | Characterize recovery of function over time. Document presurgical and postsurgical (or other intervention) changes in function |
Neuropsychological rehabilitation | Supervised by a clinical neuropsychologist | Targeted or general improvement in some aspect of neuropsychological function. To facilitate functional outcome |
Neuropsychological monitoring during surgery | Clinical neuropsychologist or cognitive neuroscientist | Characterize brain areas concerned with specific neuropsychological functions for clinical and/or research purposes |
Postsurgical neuropsychological testing with implanted electrodes (e.g., on-off stimulation) | Cognitive neuroscientist or clinical neuropsychologist | Characterize brain areas concerned with specific neuropsychological functions for research purposes |
Postsurgical neuropsychological testing on groups of patients with specific excisions (e.g., anterior temporal lobe) | Cognitive neuroscientist or clinical neuropsychologist | Characterize brain areas concerned with specific neuropsychological functions for research purposes |
Licensed and clinically trained neuropsychologists typically use generally accepted test batteries for their assessment procedures so that interpretation of the test results can be based on a quantitative summary using previously acquired normative data that are typical for a rigidly administered battery, or instead, a neuropsychologist can make a qualitative judgment of the results from a somewhat idiosyncratic test battery (which usually has a core of tests that have normative data). 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 colleagues1). For the vast majority of patients tested by clinical neuropsychologists, a pattern of performance emerges with strengths and weaknesses 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 may have somewhat narrow interests (e.g., concerned with 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, and such information may also have clinical utility if the patient’s lesion falls within that brain region.
Although historically, clinical neuropsychological assessment was also used for diagnostic purposes, 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 in the very early stages of a dementing disease, but some neuropsychological tests may have a degree of sensitivity to change in performance to detect early impairment in these patients (e.g., in incipient idiopathic Alzheimer’s disease or the very early stages of a tumor). Besides evaluation and diagnosis, neuropsychologists also have a prominent role to play in the remediation of functional abilities.2 Such a role includes designing and application 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.
It is also worth mentioning here that at least one myth about the functions of the cerebral cortex needs burial. Conventional wisdom used to proclaim that a neurosurgeon needed to avoid language or eloquent tissue because postsurgical aphasias could significantly affect recovery and outcome. Conversely, removal of relatively large areas of the anterior frontal lobe, particular in the right hemisphere, was relatively acceptable. As the functional role of the right frontal lobe has become more apparent in the past 2 decades, it is 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 naming deficits.3 Cognitive neuroscientists are playing a major role in revealing the importance of the frontal lobes of the brain, and further findings that will help specify the functions of the human prefrontal cortex to a level equivalent to the functional assignments of the posterior cortex will be forthcoming in the next decade.4 Thus, the clinical neuropsychologist and cognitive neuroscientist can be important team members whose ability to characterize the cognitive, social, and emotional functions of a patient can be invaluable to a neurosurgical practice.
Clinical Assessment
Clinical neuropsychologists use computerized and paper and pencil tests that have undergone varying degrees of standardization so that individual patient results can be compared with a standard normative sample (for the more standardized tests, norms for older adults and adolescents will be included, as well as norms for various patient populations). The assessment can potentially range across a large number of domains of function, from tactile memory to reasoning and problem solving. In general, most domains of ability can be assessed by directly testing the patient. The patient’s social cognition, however, is usually assessed by observation and caregiver or informant reports via scales. Particularly when damage or excisions involve the frontal lobes, the patient’s insight may be compromised, and thus comparison between the patient’s self-report and that of a spouse, parent, or child will be necessary.5
Clinical neuropsychologists may rely on a standard battery of tests that are administered to all patients, such as the Halstead-Reitan Battery, an idiosyncratic, yet standardized (at least on a per test basis) set of tests covering all domains of function, or they may adapt a tailored testing regimen for individual patients, with some tests being applied because of the particular problems of an individual patient.6 Domains of function that can be objectively and quantitatively studied include intelligence, language, perception, visual recognition, attention, sensory and motor skills, spatial ability, emotional processing, and executive functions. Abbreviated tests or batteries such as the Mattis Dementia Rating Scale, Frontal Assessment Battery, or Mini-Mental State Evaluation are also available for use during a simple office visit and rarely take longer than 30 minutes to administer.7 What they lack in sensitivity, breadth, and depth, they make up for by allowing at least a minimal quantification of a patient’s neuropsychological functioning by health practitioners other than neuropsychologists who have some training in or exposure to neuropsychology. In the not too distant future, it should be possible to also objectively assess social skills directly rather than rely only on subjective family reports and patient self-reports. Many standardized batteries will take a morning and afternoon to complete as noted earlier, but this should not be surprising given that our cognitive, social, and sensorimotor abilities are neither simple nor limited in comparison to other species. Alternatively, for both insurance and practical purposes, shorter evaluations can be accomplished, particularly when a question is targeted.
Clinical Interventions
The neuropsychologist may also engage in clinical interventions of various kinds. Such clinical interventions may include cognitive remediation, management of mood states such as anxiety or depression, or vocational-style retraining. As part of rehabilitation, cognitive remediation has taken on significant importance in helping patients recover from brain injuries, such as those suffering from traumatic brain injury or the long-term effects of needed surgical excisions. Although rehabilitation medicine continues to lag behind other specialties in performing efficacy studies for general or specific interventional strategies, even the structuring and attention provided by a clinical neuropsychologist to the patient during the recovery period may help enable that person and family to cope with or compensate for persistent neuropsychological deficits. Neuropsychological interventions are usually time limited, require practice at home, and encourage caregiver involvement. When initially practiced, cognitive remediations required the active involvement of a clinician several times a week for several hours each day. With the advent of the World Wide Web and computer sophistication, many patients are able to import the tasks that they are assigned to their home computer and practice at home, thereby mitigating the need for daily or frequent trips to the clinic. Despite its demonstrated efficacy in individual patients or small groups when the therapy is targeted, replications of efficacy in large samples are often hard to find, there are too many rehabilitation software programs marketed without any proof of effectiveness, and it may be difficult to control for patient and family involvement in the therapy when the majority of practice takes place at home.8 Too often the therapy is administered without a clear vocational or social target, and outcomes can be clouded by this lack of therapeutic mapping to real-life needs.