Comparison of neurocognition between drug-free patients with schizophrenia and bipolar disorder.

It is often difficult to make a differential diagnosis between schizophrenia and bipolar disorder because of the overlapping symptoms. The patients of both disorders have been shown to have neurocognitive deficits. In this study, a computerized battery of neurocognitive tasks, COGLAB, was administered to four participant groups: 30 patients with positive schizophrenia, 22 patients with negative schizophrenia, 27 patients with bipolar disorder, and 28 normal controls. All the patients were drug-free for at least 1 month. The tasks included Mueller-Lyer illusion, reaction time, size estimation, a variant of the Wisconsin Card Sorting Test, backward masking, and Asarnow continuous performance. Discriminant analyses were used to investigate the differences among the four groups. Results indicated that COGLAB correctly classified 73.5% of the cases of negative schizophrenia and bipolar disorder. The best discriminative tasks were card sort, Asarnow continuous performance, and backward masking. The results of this study were also compared with results of a previous study with medicated patients. Neurocognitive tasks had better discriminative power for medicated patients with schizophrenia and bipolar disorder than for drug-free patients. Moreover, medication effects did not seem to significantly change the pattern of the neurocognitive task responses of patients with schizophrenia.