Electromyographic evidence of a multiple motor system: implications for apraxia.

Geschwind (1975) postulated that a multiple motor system accounts for a discrepancy in apraxias in response to commands for truncal and limb movements. Kuypers (1968) provided experimental evidence of a multiple motor system in primates. We present evidence of this multiple motor system in the form of Fourier-transformed electromyographic data in humans of the predominantly short duration motor units for discrete control in hand musculature and the predominantly longer duration motor units in the truncal musculature. Furthermore, the right and left erector spinae muscles had different Fourier-transformed electromyographic data which, in our opinion, represent the medial motor system used by apraxias.