Slow cortical potentials (SCPS) in schizophrenic patients during performance of the Wisconsin card-sorting test (WCST).

Fifteen schizophrenic patients (diagnosed according to DSM-III-R) and 15 age- and education-matched controls were tested on a computerized version of the Wisconsin card-sorting test (WCST). Slow Cortical Potentials (SCPs) were recorded throughout the performance from frontal, central and parietal electrode sites. As expected, the patients were impaired on the WCST, achieving fewer categories overall and incurring significantly more "unique" errors, although they were not significantly more perseverative than the controls. The patients did not display a generalized impairment in SCPs, differences between the groups emerging only before presentation of the key-cards and after presentation of the feedback regarding the correctness of the response. Neither the choice-card at the beginning of the trial, nor the presentation of the key-cards resulted in attenuated Evoked Potentials (EPs) in the patients. The lack of any abnormality in EPs suggests that the reason for the poor performances of schizophrenic patients on the WCST lies elsewhere than in perceptual stimulus processing. Contrary to expectations no specific impairment in frontal SCPs was detected.