Long-latency feedback coordinates upper-limb and hand muscles during object manipulation tasks

Abstract

Suppose that someone bumps into your arm at a party while you are holding a glass of wine. Motion of the disturbed arm will engage rapid and goal-directed feedback responses in the upper-limb. While such responses can rapidly counter the perturbation, it is also clearly desirable not to destabilize your grasp and/or spill the wine. Here we investigated how healthy humans maintain a stable grasp following perturbations by using a paradigm that requires spatial tuning of the motor response dependent on the location of a virtual target. Our results highlight a synchronized expression of target-directed feedback in shoulder and hand muscles occurring at ∼60ms. Considering that conduction delays are longer for the more distal hand muscles, these results suggest that target-directed responses in hand muscles were initiated before those for the shoulder muscles. These results show that long-latency feedback can coordinate upper limb and hand muscles during object manipulation tasks.

Significance Statement: Skilled object manipulation relies on fine control of finger forces applied on the held objects. A prevailing hypothesis suggests the nervous system predicts the consequence of motor commands to anticipate self-generated loads arising when we move the objects around. Here we show that following an external perturbation, motor responses in upper-limb and hand muscles expressed synchronized, target-directed modulation in ∼60ms. This finding cannot be explained by internal predictions from forward models, as processing and conduction times expected in this framework imply measurable delays between the expression of flexible feedback in upper-limb and hand muscles. Instead, our results suggest that in such context, stable control of grasp is also mediated by goal-directed feedback coordination of upper-limb and hand muscles.