Pathophysiology of ‘positive’ thought disorder in schizophrenia

Formal thought disorder is a characteristic feature of psychosis, but little is known of its pathophysiology. We have investigated this in schizophrenia using positron emission tomography (PET). Regional cerebral blood flow was measured using H2(15)O and PET while six people with schizophrenia were describing a series of 12 ambiguous pictures which elicited different degrees of thought-disordered speech. In a within-subject design, the severity of 'positive' thought disorder was correlated with cerebral blood flow across the 12 scans in each subject. Verbal disorganisation (positive thought disorder) was inversely correlated with activity in the inferior frontal, cingulate and left superior temporal cortex, and positively correlated with activity in the parahippocampal/anterior fusiform region bilaterally, and in the body of the right caudate (P < 0.001). The total amount of speech produced (independent of thought disorder) was positively correlated with activity in the left inferior frontal and left superior temporal cortex. The severity of positive thought disorder was inversely correlated with activity in areas implicated in the regulation and monitoring of speech production. Reduced activity in these regions may contribute to the articulation of the linguistic anomalies that characterise positive thought disorder. The positive correlations between positive thought disorder and parahippocampal/anterior fusiform activity may reflect this region's role in the processing of linguistic anomalies.