DORSOLATERAL PREFRONTAL CORTEX DYSFUNCTION IN THE MAJOR PSYCHOSES - SYMPTOM OR DISEASE SPECIFICITY

Neurophysiological deficits in the left dorsolateral prefrontal cortex (DLPFC) have been described in positron emission tomography studies o f schizophrenia and depression. In schizophrenia and depression this d eficit has been associated with the syndromes of psychomotor poverty a nd psychomotor retardation, respectively. Such findings lead to a pred iction that DLPFC dysfunction is symptom rather than disease related. This prediction was empirically tested in a retrospective study that p ooled data from 40 patients meeting research diagnostic criteria for d epression and 30 patients meeting DSM-III R criteria for schizophrenia . The patients were categorised into those with and without poverty of speech, a symptom that is an observable manifestation of psychomotor impairment. The profile of regional cerebral blood flow (rCBF), measur ed in all subjects under resting conditions, was subsequently compared in these two groups. Patients with poverty of speech had significantl y lower rCBF in the left DLFPC. This reduction of rCBF was independent of diagnosis. The findings support the view that the study of symptom s, or symptom clusters, can provide information additional to that of traditional diagnostic systems in the study of the major psychoses.