Cortical contributions to the stretch reflex response in biceps brachii.

Long-latency components of the stretch reflex may aid in organizing multi-joint movements and posture. The aims of this study were to investigate if the M2 response in biceps brachii is mediated through a trans-cortical pathway. Ipsi-lateral and contra-lateral transcranial magnetic stimulation, combined with a variety of ramp-and-hold perturbations in which the subject was instructed to either intervene or not resist were applied to biceps brachii. The biceps M2 response modulates with task and can be facilitated through contra-lateral TMS. This is consistent with the existence of a trans-cortical pathway. Attempts to inhibit this pathway, possibly affecting the long-latency stretch reflex have not yet produced consistent results.