Synchronous development of motor cortical output to different muscles in the kitten.

Previous observations indicate that the output linkages from motor cortex (area 4) to triceps brachii motoneurons develop relatively late in the postnatal kitten. Responses in multiple, simultaneously-recorded EMG's from facial, forelimb and proximal hindlimb musculature to intracortical microstimulation appear over gestational days 107-111 (about 41 days postnatally). Thus, output from the motor cortex to alpha motoneurons develops in a synchronous, rather than a sequential manner across the area 4 homunculi.