Fig. 2. Experimental design for surgical neural input rewiring using donor nerves with high-, low-, or original axonal capacity.

The sternomastoid muscle was used as a target muscle due to its large volume and native low neural input. Three groups were investigated: high-capacity nerve reinnervation (A), low-capacity nerve reinnervation (B), and reinnervation with the native neural input (C). (A) The mandibular branch of the facial nerve was used as a high-capacity donor nerve. The mandibular branch was transferred to the motor entry point of the sternomastoid muscle and coaptated using 11-0 suture. (B) The ulnar nerve was used as a low-capacity donor of neural input to the same target muscle. (C) The motor branch of the sternomastoid muscle was transected and immediately repaired using 11-0 suture to allow the reinnervation of the muscle via the original motor neural sources.