Isometric force control in schizophrenic patients with tardive dyskinesia.

Force control (FC) function, considered to be a constituent component of motor output, was investigated in psychiatric patients with dyskinetic impairments. Twenty-one patients with mild-to-moderate tardive dyskinesia were compared to 25 nondyskinetic patients on an FC test for both hands and oromandibular region. Results indicate that FC impairment is readily observed in dyskinetic subjects. The FC steadiness (i.e., the ability to maintain a sustained force output) in dyskinetic and control subjects was found to be inversely proportional to the amount of force generated. This method provides an objective, simple, and precise quantification of motor impairment along a force-defined continuum. It may be useful in studying tardive dyskinesia and the effects of neuroleptic medication on motor output control.