PT  - JOURNAL ARTICLE
AU  - Jeffrey Weiler
AU  - Paul L. Gribble
AU  - J. Andrew Pruszynski
TI  - Rapid feedback responses are flexibly coordinated across arm muscles to support goal-directed reaching
AID  - 10.1101/143008
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 143008
4099  - http://biorxiv.org/content/early/2017/05/27/143008.short
4100  - http://biorxiv.org/content/early/2017/05/27/143008.full
AB  - Rapid feedback responses can be evoked in wrist muscles when elbow muscles are unexpectedly stretched during goal-directed reaching. Here we examined the flexibility of this coordination. Participants used a planar three degree-of-freedom (shoulder, elbow, wrist) exoskeleton robot to move a cursor to a target following an elbow flexion perturbation. In our first experiment, the cursor was mapped to the veridical position of the robot handle, but participants grasped the handle with two different hand orientations (thumb pointing upward or thumb point downward). We found that large long-latency stretch responses (i.e., muscle activity 50-100 ms following a perturbation) were evoked in wrist extensor muscles when wrist extension helped move the cursor to the target (i.e., thumb upward), and in wrist flexor muscles when wrist flexion helped move the cursor to the target (i.e., thumb downward). In our second experiment, participants grasped the robot handle with their thumb pointing upward, but the cursor’s movement was either veridical, or was mirrored such that flexing the wrist moved the cursor as if the participant extended their wrist, and vice versa. We found that, after extensive training, large long-latency stretch responses were evoked in wrist flexor muscles when wrist flexion helped move the cursor to the target (i.e., mirror mapping), and in wrist extensor muscles when wrist extension helped move the cursor to the target (i.e., veridical mapping). Taken together, our findings highlight the flexible routing of long-latency stretch responses and how this coordination supports goal-directed reaching.New and Noteworthy We show that the same elbow perturbation evokes long-latency stretch responses in either wrist flexor or extensor muscles depending on which of these muscle groups help achieve the goal of a reaching task. Our findings add to the growing body of work detailing how rapid feedback responses support purposeful goal-directed movement.