Topographical analysis of motion-triggered visual-evoked potentials in man.

PURPOSE The middle temporal (MT) area of the cortex of the monkey is involved in visual motion analysis. Previous studies using brain-imaging techniques have shown that the area around the anterior occipital cortex in man is homologous to the area MT of the monkey. In this study, we investigated the cortical components of motion-triggered visual evoked potentials and their topography in the visual cortex of man. METHODS Visual evoked potentials to the onset of a visual motion stimulus (m-VEPs) were recorded from 5 normal subjects aged 25 to 34 years. A random dot pattern was used as the stimulus for the m-VEPs. The dots moved horizontally to the right and then to the left alternately for 500 milliseconds with interstimulus intervals of 1500 milliseconds. The speed of motion was varied in five steps from 5-25 degrees/s. Fifteen electrodes were placed on the occiput around O(z) at 5-cm intervals. Color contour maps showing the distribution of voltage over the 15 electrodes at latencies ranging from 0-200 milliseconds with a 20-millisecond interval were made for each subject. These were coregistered with three-dimensional magnetic resonance images of the same brain to specify the topography of the main components of the m-VEPs in relation to the sulcal and gyral pattern of the visual cortex. RESULTS We consistently observed a positive wave with a peak latency of about 100 milliseconds (P100) and a negative wave with a peak latency of about 150 milliseconds (N150) for all subjects. Topographical analysis showed that P100 was dominant in a relatively wide area caudal to O(z), whereas N150 was dominant in a relatively small area posterior to the right anterior occipital sulcus, which included the area corresponding to the area MT in man. CONCLUSIONS These findings suggest that N150 represents the activity of the area MT in the human visual cortex related to motion perception.