Prefrontal gyral folding and its cognitive correlates in bipolar disorder and schizophrenia

We sought to address whether dorsal or ventral prefrontal gyrification is abnormal in bipolar disorder and to determine its diagnostic specificity and cognitive associations. Forty-two out-patients with bipolar disorder, 28 with schizophrenia and 37 controls underwent magnetic resonance imaging. All subjects also underwent IQ and executive assessments using tasks whose performance has been localized to the ventral or dorsal prefrontal cortex. Cortical folding was quantified using the gyrification index (GI) and related to the cognitive measures. Patients with bipolar disorder showed reduced prefrontal gyrification compared with controls but did not differ from patients with schizophrenia. Neither ventral nor dorsal GI was preferentially affected in either disorder. Current IQ was positively and significantly correlated with GI. Patients with bipolar disorder and patients with schizophrenia have reduced prefrontal gyrification affecting both ventral and dorsal subregions. These reductions were significantly associated with cognitive impairments occurring in both disorders.