Spatiotemporal activity of a cortical network for processing visual motionrevealed by MEG and fMRI

Spatiotemporal activity of a cortical network for processing visual motion revealed by MEG and fMRI. J. Neurophysiol. 82: 2545-2555, 1999. A sudden ch ange in the direction of motion is a particularly salient and relevant feat ure of visual information. Extensive research has identified cortical areas responsive to visual motion and characterized their sensitivity to differe nt features of motion, such as directional specificity. However, relatively little is known about responses to sudden changes in direction. Electrophy siological data from animals and functional imaging data from humans sugges t a number of brain areas responsive to motion, presumably working as a net work. Temporal patterns of activity allow the same network to process infor mation in different ways. The present study in humans sought to determine w hich motion-sensitive areas are involved in processing changes in the direc tion of motion and to characterize the temporal patterns of processing with in this network of brain regions. To accomplish this, we used both magnetoe ncephalography (MEG) and functional magnetic resonance imaging ( fMRI). The fMRI data were used as supplementary information in the localization of ME G sources. The change in the direction of visual motion was found to activa te a number of areas, each displaying a different temporal behavior. The fM RI revealed motion-related activity in areas MT+ (the human homologue of mo nkey middle temporal area and possibly also other motion sensitive areas ne xt to MT), a region near the posterior end of the superior temporal sulcus (pSTS), V3A, and V1/V2. The MEG data suggested additional frontal sources. An equivalent dipole model for the generators of MEG signals indicated acti vity in MT+. starting at 130 ms and peaking at 170 ms after the reversal of the direction of motion, and then again at similar to 260 ms. Frontal acti vity began 0-20 ms later than in MT+, and peaked similar to 180 ms. Both pS TS and FEF+ showed long-duration activity continuing over the latency range of 200-400 ms. MEG responses in the region of V3A and V1/V2 were relativel y small, and peaked at longer latencies than the initial peak in MT+. These data revealed characteristic patterns of activity in this cortical network for processing sudden changes in the direction of visual motion.