[Transformation of an afferent tactile signal into a motor command in the cat motor cortex]

The activity of 112 units of the cat precruciate motor cortex was studied simultaneously with the performance of a placing reaction of the foreleg to tactile stimulation of its distal parts. The response latency to the tactile stimulation of the foreleg was 30-40 ms for the electromyographic response of m. biceps brachii and 20 +/- 10 ms for the earliest-responses of the motor cortical neurons. The electrical reaction of m. biceps brachii occured 5-10 ms after the termination of the electrical stimulation of the cortex by a puls series (the series duration was 25 ms, the pulse duration 0.2 ms, frequency 400 per s). Two different types of excitatory reactions of the motor cortex units were found: the sensory (s) ones occured at each tactile stimulus and did not depend on the presence or absence of the foreleg motion; the motor (m) type of reactions developed simultaneously with the motor placing reaction of the foreleg only. The minimal latency of cortical m- and s-type discharge was 20 +/- 10 ms. Electrical stimulation (5-25 micronA) through the microelectrode placed in the locus of neuronal activity which increased during active flexion of the foreleg, provoked in 70% of cases the electrical response in m. biceps brachii.