MOTOR MECHANISMS IN SCHIZOPHRENIC-PATIENTS WITH TARDIVE-DYSKINESIA

A specific aspect of the motor output of patients with tardive dyskine sia was investigated with an experimental procedure referenced in forc e control function (i.e., the maintenance of sustained force output). We hypothesized that response output (button press) at a given level w ould be significantly altered when preceded by an output of a higher f orce than when preceded by an output of a lower force. The difference could be interpreted as a behavioral measure of fatigability and/or th reshold change, and its quantitative aspects could serve as a marker o f motor impairment. Three groups of subjects participated in the study : schizophrenic patients with tardive dyskinesia (TD), schizophrenic p atients without tardive dyskinesia, and normal control subjects. The t est used was a target-matching task with force output ranging from 5 t o 560 cN. Three dependent measures were used: output force, steadiness of force maintenance, and latency of target capture. Results indicate d that precedent output at the previous trial significantly altered fo rce, but even better group separation was attained with the measure of steadiness. The TD schizophrenic group's performance was least effici ent, the control group's was most efficient, and the non-TD schizophre nic group's performance was intermediate. The principal conclusions re ached were that the target-matching response reflects mechanisms relat ed to both fatigability and recruitment of motor units involved in out put control.