Physiological demonstration of multiple representation in the forelimb region of the cat motor cortex.

Earlier studies in primates have demonstrated a double representation of the distal forelimb in area 4. In this study intracortical stimulation was used to map the representation of the forelimb in area 4 of the cat. Maps of individual animals revealed two spatially separate representations for the distal forelimb in area 4. Two "digit zones," regions in which threshold stimulation evoked contractions limited to digit musculature, were seen in all animals. Although the absolute location of the two digit zones varied among animals, the zones were always separated by a field in which more proximal musculature was represented. In some experiments EMG activity was monitored from selected forelimb muscles in order to determine the muscles represented in the two zones. Activity of the same digit muscle could be evoked by stimulation in each digit zone. The analysis demonstrated that some digit muscles were represented in both the digit zones. Thus, this study demonstrates that multiple representation of the distal forelimb in area 4 is not an isolated, species-specific phenomenon, but is likely to be a generalized pattern of motor cortex organization.