[Voluntary control of the activity of the individual motor units of different muscles]

16 subjects learned in feedback experiments to control activity of separate motor units (MU) in muscles of face, neck, hand, forearm, arm, thigh and crus. The test consisted in modulation of frequency and duration of the MU firing. The time total of the test, number of MU acting correctly, ratio of the "controllable" units to the number of units studied in a particular muscle, were recorded. MUs of the same muscle were found to be controllable to a different extent. All the muscles hand unit resisting learning for any period of time. No correlation between the muscle cortical representation and the percentage of the "controllable" units in it, was found.