Perceptual factors contribute to akinesia in Parkinson’s disease
Résumé
Parkinson's disease (PD) patients have longer reaction time (RT) than age-matched control subjects. During the last decades, conXicting results have been reported regarding the source of this deWcit. Here, we addressed the possibility that experimental inconsistencies originated in the composite nature of RT responses. To investigate this idea, we examined the eVect of PD on diVerent processes that compose RT responses. Three variables were manipulated: the signal quality, the stimulus-response compatibility and the foreperiod duration. These variables have been shown to aVect, respectively, the ability to extract the relevant features of the stimulus (perceptual stage), the intentional selection of the motor response (cognitive stage) and the implementation of the muscle command (motor stage). Sixteen PD patients were tested on and oV-medication and compared with an age and gender-matched control group. Results indicated that degrading the legibility of the response stimulus aVected the latency of simple key-press movements more dramatically in the oV-medication PD group than in the control population. The stimulus-response compatibility and the foreperiod duration had similar eVects in the two groups. Interestingly, the response slowing associated with the degradation of the stimulus was the same whether the patients were on or oV dopaminergic medication. This suggests that the high-level perceptual deWcits observed in the present study do not have a dopaminergic origin.