Impaired Wisconsin Card Sorting Test (WCST) performance has been one critical piece of evidence suggesting frontal lobe dysfunction in schizophrenia. However, the specific cognitive processes underlying impaired performance have not been identified. Impaired WCST performance in schizophrenia might in part reflect a fundamental working memory deficit.
We examined the performance of 30 normal subjects and 36 patients with schizophrenia on a neuropsychological battery including a novel measure of working memory—letter-number (LN) span.
Patients with schizophrenia were impaired on LN span performance, which was also highly correlated with WCST performance (r=0.74). Between-group WCST differences were eliminated when we covaried LN span. Regression analyses suggested that LN span performance predicted the WCST category achieved score, whereas measures of set shifting, verbal fluency, and attention were predictive of perseveration.
Working memory may be a critical determinant of one aspect of WCST performance in schizophrenia.