Differences in early dynamic connectivity Between visual expansion and contraction stimulations revealed by an fMRI-directed MEG approach

Background And Purpose: The human visual system responds asymmetrically to visual motion stimuli in opposite directions due to the involvement of the same brain areas but different operating processes. The expansion mode is thought to invoke a vigilance mechanism, whereas the contraction mode does not. Methods: To investigate discrepancies between these modes, we produced dynamic connectivity maps based on mutual information between visual-evoked dipole sources of magnetoencephalography, which were steered by visual activity patterns in functional magnetic resonance imaging under two motion-stimulus modes. Results: In the expansion mode, information was conveyed from V1 at 50-75 ms after motion onset, fed forward to V3A and then V5. Top-down connectivity paths were evident after a latency of 100 ms. Many of these interactions occurred within 200 ms. However, in the contraction mode, information was conveyed from V3A to V5, followed by feedback, but regained from V1 after a latency of 250 ms. Although these interactions were delayed by about 250 ms, they were completed within 500 ms. Conclusions: These findings show that detect spatiotemporal differences between expansion and contraction modes can be readily detected using time-flow charts. Moreover, delay interactions could be insensitive to object motion away from the observer.