Figure 2.

The visuomotor step-tracking task and EMG examples. (A) Flexion and extension movements rotated the manipulandum in the horizontal plane and thereby controlled the horizontal position of an onscreen cursor. On each behavioural trial, after a start-position hold period (random duration, 2–5 s), the animal was required to move the cursor toward one lateral target (left or right direction chosen at random). Examples of angular velocity (B) and muscle activity (C) observed during voluntary movements before (black) and after (red) MPTP administration. Single trial velocity traces are plotted relative to the computed time of movement onset (vertical dashed line). Note the accurate detection of movement onset in both pre- and post-MPTP data. In C, peri-movement means of the digitized EMG signals are shows for two muscles for all valid extension (EXT) and flexion (FLX) movements. Note that the y-scale is inverted for FLX movements in B and C.