Background. Formal thought disorder is a core symptom of schizophrenia. It is associated with a reversed lateralization of the superior temporal cortex volume, an area that is implicated in lexical retrieval. We investigated the neural correlates of word retrieval during continuous speech in patients with formal thought disorder using functional magnetic resonance imaging (fMRI).

Methods. Blood oxygenation level dependent (BOLD) contrast was measured with fMRI while six patients with schizophrenia and six healthy control subjects spoke about seven Rorschach inkblots for 3 min each. Subjects produced varying amounts of speech during each run. In a within subject design, the number of words produced was correlated with the BOLD contrast in the two runs in each participant who showed the highest variance of speech output.

Results. In control subjects, the amount of speech produced was mainly correlated with activation in the left superior temporal gyrus. In the patient group, the main correlations were in the right superior temporal gyrus.

Conclusions. During the production of continuous speech, patients with formal thought disorder showed a reversed laterality of activation in the superior temporal cortex. This is consistent with findings of perturbed hemispheric interaction in schizophrenia, particularly in patients with formal thought disorder.