The effect of external stimulation on arousal and motor performance in Parkinson's disease. An experimental study

Motor performance in 8 bradykinetic parkinsonian patients and 8 controls matched for age and sex was studied using measurement of the successive reaction time (SRT) with and without an external warning stimulus. The difference between the SRTs with and without warning was used as a measure of arousal. In both groups a warning stimulus reduced the SRT from a peripheral muscle. Motor performance in the control group following external arousal was significantly better than that in the parkinsonian group. These results suggest that parkinsonian bradykinesia is partially caused by an arousal defect of the 'exo-evoked' attentional system of the ascending reticular formation of the brainstem and that a defect in catecholamine turnover in these structures plays an important role in the mechanism of impaired arousal in these patients.