The experimental protocol is illustrated in Fig. 1B. In the pressing task, subjects were asked to perform self-initiated press and release movements using the index finger at a comfortable rate (2 trials of 3 min each). In the slow tapping tasks (6 trials of 30 s each, two blocks), subjects were instructed to tap at a slow rate (instruction “tap at your own comfortable speed”). In the fast tapping tasks [10 trials of 12 s or 15 s each, two blocks (9 patients and 11 controls tapped for 12 s/trial in the second block of fast tapping tasks)], subjects were instructed to tap at their fastest speed (instruction: “tap as fast as possible”). During the slow and fast tapping tasks, subjects were asked to tap with their index finger maximally extended. Between trials and tasks, subjects were allowed sufficient time to rest, to minimize fatigue. Two different conditions (blocks) were designed for each of the tapping tasks (Fig. 1C). These conditions differed in the absence (FB-) or presence (FB+) of feedback as to whether the index finger extension had met
