The transcortical reflex triggered by cutaneous or muscle stimulation in the cat with a penicillin epileptic focus: relative importance of regions 3a and 4.

After establishment of a cortical penicillin epileptic focus in the cat, stimulation of an anterior paw muscle can evoke a late myographic response (LMR) in the same muscle via a transcortical reflex. It is shown here that (1) an LMR can also be obtained with cutaneous stimulation in the region of the muscle; (2) an LMR cannot be elicited when the focus in on area 3a; (3) after inactivation of area 3a by TTX, the motor cortex evoked potential and spike thresholds are increased for proprioceptive but not for cutaneous stimulation, and the LMR persists. It is concluded that area 4 is the critically important structure for the triggering of an LMR. The results concerning area 3a are discussed in terms of this region's efferent connections to the motor cortex and to the spinal cord.