Fig. 4.

Quantification of musculotopic arrangement of motor fibers. We assessed the musculotopic organization of nerve fibers by comparing the muscle activated by each USEA electrode with the muscles activated by neighboring USEA electrodes. For each electrode capable of activating a muscle, we calculated the probability that a neighboring electrode would activate the same muscle from chance alone. The actual number of neighboring electrodes that preferentially activated the same muscle was consistently higher than the number expected from chance (i.e., the actual − expected difference was >0), indicating a musculotopic arrangement in which motor fibers to a given muscle were close together within the nerve. This pattern held for muscles of all types and each nerve individually.