Planning dysfunction in schizophrenia: impairment of potentials preceding fixed/free and single/sequence of self-initiated finger movements.

To test the hypothesis of a planning dysfunction in schizophrenia using a precise temporal definition, the readiness potential (RP), a negative cortical wave preceding self-initiated movements and reflecting motor preparation processes, was studied in patients under stable medication and in controls. The supplementary motor area (SMA), known to be involved in the generation of the RP, has also been implicated in movement selection (fixed versus free) and complexity (single versus sequence). This is the first study using RP for the assessment of the influence of these factors on motor preparation in schizophrenics. Our results show that schizophrenics' RP amplitude is significantly lower than in controls at central and contralateral electrodes. However, RP amplitude increases with task difficulty in both groups, offering important new insight into classical SMA hypoactivation in schizophrenics performing motor tasks. Topographic analysis shows that RP amplitude is, for both groups, significantly higher in sequence than in single movements at fronto-central sites and higher for free than for fixed movements at centro-parietal sites. Finally, RP onset occurs significantly later in schizophrenics than in controls. These results support the view of a motor-preparation and decision-making dysfunction in schizophrenia. They are interpreted within the framework of a fronto-striatal disorder in this disease.