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 p recise temporal definition, the readiness potential (RP), a negative cortic al 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 generatio n of the RP, has also been implicated in movement selection (fixed versus f ree) and complexity (single versus sequence). This is the first study using RP for the assessment of the influence of these factors on motor preparati on in schizophrenics. Our results show that schizophrenics' RP amplitude is significantly lower than in controls at central and contralateral electrod es. However, RP amplitude increases with task difficulty in both groups, of fering important new insight into classical SMA hypoactivation in schizophr enics performing motor tasks. Topographic analysis shows that RP amplitude is, for both groups, significantly higher in sequence than in single moveme nts at fronto-central sites and higher for free than for fixed movements at centro-parietal sites. Finally, RP onset occurs significantly later in sch izophrenics than in controls. These results support the view of a motor-pre paration and decision-making dysfunction in schizophrenia. They are interpr eted within the framework of a fronto-striatal disorder in this disease.