Redundant-signals effects on reaction time, response force, and movement-related potentials in Parkinson's disease

Studies using transcranial magnetic stimulation have established that patie nts with Parkinson's disease have increased motor cortex excitability. Rely ing on current evidence that the redundant-signals effect has its source in the motor system, we investigated whether, as a result of cortical hyperex citability, Parkinson's disease patients demonstrate an enhancement of this effect. Eight patients with moderately severe Parkinson's disease and nine healthy control subjects participated in a task requiring simple manual re sponses to visual, auditory, and combined auditory-visual signals. During t he task, motor cortex activation was recorded by means of movement-related EEG potentials, while responses were measured via isometric force recording s. The movement-related potentials and the force measures both yielded supp ort for the view that the redundant-signals effect is partially caused in t he motor system. However, the facilitatory effect of bimodal as compared to unimodal stimulation (i.e. the redundant-signals effect) was of the same s ize in Parkinson's disease patients and control subjects, as expressed in l atency measures of the movement-related potentials and the force signals. W e conclude that the redundant-signals effect is not enhanced in Parkinson's disease and that the mechanisms underlying this effect are probably not in fluenced by the increased motor cortex excitability found in this disease.