Using a custom-made multiple-site optical recording system, we have studied the characteristics of spatiotemporal pattern of neural activity in the sensory cortex. The somatic evoked response in the rat somatosensory cortex is initiated from the somatotopically corresponding sites and propagates over the entire region of the somatosensory cortex. In this presentation, we analyze the effect of the preceding forelimb-induced neural activity on the hindlimb-induced neural activity with regard to the spatiotemporal pattern in the somatosensory cortex. The left somatosensory cortex of the anesthetized rat was exposed and stained with a voltage-sensitive dye (RH-414). Forelimb- and hindlimb-induced neural responses were successively elicited by electrical stimulations (1 mA, 0.5 msec) with the inter-stimulus intervals (ISIs) of 0, 20, 50, 100, 200 or 300 msec. When the ISI was 0 or 20 msec, the two propagating waves ran into each other on a collision line between the respective initiation sites and disappeared. At the ISI of 50 msec, no occurrence of hindlimb induced-response was observed. At the ISI of 100 msec, addition of the reduced hindlimb response to the forelimb response was observed at the initiation site of hindlimb response. When the interval was 200 msec and longer, the forelimb-induced propagating wave had passed the initiation site of the hindlimb response before the hindlimb response was initiated. In this condition, the hindlimb response was observed, but the amplitude and the extent of the propagation area were both decreased. These results suggest that the somatic evoked wave suppresses the occurrence or reduces the propagation of another one.