Motor program memory storage in Parkinson's disease patients tested with a delayed response task.

We used a delayed response paradigm to test the hypothesis that the prolonged reaction time in patients with Parkinson's disease (PD) is related to a deficiency in their ability to store a motor program in memory while waiting to move. PD patients, both on and off medication, were compared with age-matched normal subjects during arm movements directed toward a target light. The target light was displayed either during a 3- to 9-s delay or for only 1 s followed by a 2- to 8-s delay before the go signal. At the end of the delay, subjects were required to begin movement rapidly. The reaction time of PD patients was longer than normal and increased slightly when the patients were off medication. The patients had no excessive increase in reaction time with delay in either task compared with the control subjects. We conclude that patients with PD can hold a motor program in memory storage for at least 8 s.