[Neural correlates of "negative" formal thought disorder]

Formal thought disorder (FTD) is a core feature of schizophrenia, but its pathophysiology is poorly understood. It can be conceptualised as 'positive' (e.g. incoherence, neologisms) or 'negative' (e.g. poverty of thought) thought disorder. We investigated the neural correlates of negative FTD. Blood oxygenation level-dependent (BOLD) contrast was measured using functional magnetic resonance imaging (fMRI) while six patients with schizophrenia and six healthy control subjects spoke about seven Rorschach inkblots for 3 min each. Varying degrees of thought-disordered speech were elicited during each run. In a within-subject design, the degree of negative thought disorder, conceptualised as 'poverty of speech' (Liddle et al. (2002) Thought and Language Index. Br J Psychiatry) was correlated with BOLD contrast in the two runs per patient showing the highest variance in this phenomenon. The degree of poverty of speech correlated positively mainly with activation in the right inferior parietal lobe (BA 40), middle frontal gyrus (BA 46), cuneus (BA 18), and the left posterior cingulate (BA 31). Negative correlations were evident in the left hippocampal/fusiform gyrus (BA 35/36/37). The severity of negative FTD correlates with activation in areas previously implicated in autobiographic episodic memory. During symptoms behaviourally characterised as negative, patients may experience rich memories and associations.