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Haidong Lu, Gang Chen, Anna Roe; Motion processing in the ventral pathway: Evidence for direction maps in macaque V2 and V4. Journal of Vision 2009;9(8):743. doi: 10.1167/9.8.743.
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© ARVO (1962-2015); The Authors (2016-present)
Motion processing in monkey visual cortex occurs in the dorsal pathway V1 to MT. However, neurons sensitive to motion directions were also found in many ventral areas including V2 and V4. The structure and function of direction selective neurons in these areas are less studied. Using intrinsic signal optical imaging, we imaged cortical response to moving stimuli (gratings and random dots) in both anesthetized and awake, behaving macaque monkeys. Cortical areas V1, V2 and V4 were imaged in the same map to facilitate comparisons. Our preliminary results showed that, unlike the primary visual cortex in cats and ferrets, macaque V1 does not contain a direction map. However, cortical regions that were preferentially activated by moving stimuli were found in two downstream areas V2 and V4 (the ventral pathway). These motion-sensitive regions in V2 and V4 contain directional-selective domains and form patches of direction maps. In V2, the motion direction maps are located in the thick stripes and exhibit overlap with orientation maps. In V4, direction-selective domains avoid both color-selective regions and orientation-selective regions. Based on these observations and our previous finding of motion contour selectivity in V2 (Lu et al., 2007, VSS), we suggest that ventral stream areas V2 and V4 may also play important roles in analyzing motion-related information, perhaps, for example, for the purpose of figure-ground segregation based on motion contrast.
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