Effects of response readiness on reaction time and force output in people with Parkinson's disease.

Previous research investigated effects of response readiness in neurologically normal subjects by manipulating the probability of responding. With a high probability of responding, reaction time is fast and the level of response force is low compared with conditions with a low probability of responding. An elaborated view of response readiness assumes that these effects reflect properties associated with the transmission of response activation to the motor output system. The present study employed high- and low-probability trials in a go/no-go task, to investigate whether these processes are impaired in people with mild to moderate Parkinson's disease. It was hypothesized that the patients would demonstrate abnormal patterns of response force with manipulations of response readiness. It was further hypothesized that the patients would display evidence of inability to inhibit responses on no-go trials. Both hypotheses were supported, suggesting that a basic deficit associated with Parkinson's disease is related to the transmission of response activation to the motor system. Response modulation appears to depend on the integrity of basal ganglia structures.