PURPOSE: Recent studies show that visual motion information is processed in a distributed fashion in the primate brain. However, properties and functions of motion-sensitive neurons outside the traditional V1-MT motion pathway are largely unknown. As a step towards full understanding of motion processing in the brain, we studied the functional role of motion-sensitive neurons in area V2 in macaque monkeys.
METHODS: With the guidance of optical imaging maps, we recorded from direction-selective (DS) neurons in anesthetized monkey V2.
RESULTS: Compared with DS neurons in area MT, V2 DS neurons have a much smaller receptive field center (~1.1deg) and a stronger antagonistic surround. Unlike MT neurons, they show weak motion integration (i.e. not selective to plaid directions). These features make V2 DS neurons suitable for detecting precise spatial locations of motion contrast in the visual scene. Consistently, both imaging results and single cell responses show that these neurons were preferentially activated when motion boundaries were presented in the visual scene.
CONCLUSIONS: We propose that the main functional role of V2 DS neurons is detection of local motion contrast, and this contrast information is used for shape-from-motion integration that also occurs in V2.