acquisition rate 100 frames per second
resolution 960 x 600

Video 1. Annotation of movement time points in pellet reaching task
Forelimb pellet reaching trials with overlaid task events as in Fig. 1b. The mouse
extends the arm from inside the box to outside the slit to reach for the pellet. Grasping is
temporally aligned to the onset of retraction and, after retraction stop, the mouse starts handling
the food pellet. Color code used in video is aligned to the one displayed in Fig. 1b.

Video 2. Movement variations observed in pellet reaching task
Forelimb pellet reaching trials stratified as in Fig. 3a in short versus long duration
reaches, complete reach and abbreviated reaches and reaches followed by handling or not. Note
the difference in reach duration and reach start distance from slit in short versus long reaches,
the absence of distal forelimb movements at retraction start in abbreviated reaches.

Video 3. Optogenetic stimulation of SNr neurons delays lever pressing.
Videos show control and optogenetic activation trials seen from the bottom
view. Visual cue is visible at the bottom to signal the beginning of the response time. Note
delay or absence of lever press execution upon laser exposure.