Probing prefrontal function in schizophrenia with neuropsychological paradigms.

In a recent series of studies we have attempted to clarify the nature of intellectual impairment in schizophrenia, and in particular, how patterns of dysfunction implicate specific neural systems. First, we found that acute psychotic adolescent patients displayed the same pattern of IQ scores (Performance less than Verbal) as adult chronic schizophrenic patients. We explored this deficit in problem solving by studying the performance of schizophrenic patients after receiving concrete and explicit instructions on how to do the Wisconsin Card Sorting Test, a task thought to be mediated by prefrontal cortex. We then studied the differential impact such a deficit in problem-solving strategies might have on a task thought to elicit both cognitive (prefrontal) and procedural or motor-skill (basal ganglia) processing. Procedural components appeared to be relatively more intact. We also addressed schizophrenic patients' ability to learn in other (extrafrontal) cognitive domains through verbal memory tasks and block design puzzles. Learning occurred under both conditions. We believe the overall pattern of deficit implicates primarily prefrontal neural systems, though a number of other neuropsychological functions are yet to be surveyed.