Movement-related potentials prior to self-initiated movements are impaired in patients with schizophrenia and negative signs

It has been suggested that certain symptoms of schizophrenia such as poverty of action and speech, and stereotyped action, reflect a dysfunction of "willed" actions while the processes involved in "stimulus-driven" actions remain intact. The aim of this study was to test this hypothesis by measuring movement-related potentials (MRPs) prior to self-initiated and externally triggered movements in three groups of subjects, five patients with a diagnosis of schizophrenia with high ratings of negative signs, six patients with a diagnosis of schizophrenia with high ratings of positive symptoms and six normal controls. Subjects lifted their right index finger at an average rate of once every 3 s in two conditions, either as self-initiated movements, or as a response to a tone while MRPs were recorded from frontal, frontocentral, central and parietal sites. The patients with schizophrenia and high ratings of negative signs had reduced amplitude of MRPs for the late and peak component and reduced slope of the early and late MRPs prior to self-initiated movements. These differences were not found prior to externally triggered movements. The patients with schizophrenia with higher ratings of positive symptoms did not differ significantly from the normal controls in terms of amplitude or slope of MRPs prior to self-initiated or externally triggered movements. These findings support the proposal that patients with schizophrenia, particularly those with negative signs, show impairment of willed actions but are not impaired in externally triggered movements. These deficits in willed actions may be mediated by impaired functioning of the frontostriatal loops.