[Reactions of visual cortex neurons to painful stimulation]

Responses of 18 neurones of the first cortical projection visual area to photic and nociceptive stimulation (plunging of a paw into hot water) were studied in immobilized cats. The increase in blood pressure recorded in the femoral artery served as index of pain response. During plunging the paw into hot water 14 neurones showed an increase in the frequency of spike activity by 3 times as compared to the background. The changes in spike activity preceded the increase in the arterial pressure by 1-2 sec. 12 out of 14 neurones also responded to a photic stimulus. After administration of chlorpromazin the neuronal response to the nociceptive stimulus was blocked, but the response to the photic stimulus persisted. A conclusion is made that pain excitation reaches cortical visual neurones through functional connections, which are different from those functioning during activation of the same neurones with specific photic stimulus.