The fixed points of the human cerebral motor area were stimulated electrically by square waves and the effects of altering parameters upon motor response were studied. 1) Under constant frequency of stimulation longer duration required a lower threshold. It was shown also by subcortical stimulation but the threshold was higher than that by cortical stimulation. 2) Under constant frequency of stimulation, changing of stimulating duration produced no altering of motor response at all. 3) Under constant duration of stimulation, low frequency produced a movement of distal joint but higher frequency produced proximal joint. 4) At the low frequencies, the responses followed the rate of stmulation; at higher frequencies smooth movements occurred; at very high frequencies quick jerky movements were observed. 5) At high frequencies, higher threshold produced also a motor response of proximal joint. From this fact it is regarded that the altering of motor response is not influenced by liminal voltage. From above mentioned the mechanism of altering effects upon motor responses caused by changing of stimulating frequencies is easily cleared. The reasons are due to the intricating arrangement of representations in motor cortex and the differences of threshold in every center depend upon number of cells, which are required for the motor response.