Altered sensorimotor integration in Parkinson's disease.

Transcranial magnetic stimulation (TMS) was used to investigate sensorimotor integration in the upper limb of 10 patients with Parkinson's disease and 10 age-matched controls. Non-conditioned and subthreshold conditioned (2 ms interstimulus interval) responses were recorded in the flexor and extensor carpi radialis muscles (FCR and ECR) of the more impaired (non-dominant) limb. Stimuli were delivered while the wrist joint was positioned statically at various joint angles as well as during different phases of passive movement of the wrist joint (90 degrees amplitude, 0.2 Hz). The FCR and ECR muscles remained relaxed during all stimulation. In both groups, responses in the static condition were larger when the target muscle was in a shortened position. Responses were also facilitated in the muscle shortening phases of passive movement. In both static and dynamic conditions, the extent of modulations in response amplitude was significantly reduced in the patient group. The level of intracortical inhibition (ICI) was also significantly less in the Parkinson's disease patients in static conditions. During passive movement, control subjects demonstrated a clear reduction in ICI compared with the static trials; however, the level of ICI was unchanged in the Parkinson's disease group in the dynamic condition. The results suggest an abnormal influence of afference on corticomotor excitability in Parkinson's disease. This may be related to abnormal sensory input, a defective integrative unit or an inappropriate motor response.