Motion sensitivity of human V6: a magnetoencephalography study.

Recent studies suggest the presence of a human homologue of monkey V6 in the dorsal posterior bank of the parieto-occipital sulcus. Monkey V6 comprises a retinotopic representation with relative peripheral visual field emphasis and is sensitive to visual motion. We studied sensitivity to visual motion in human parieto-occipital sulcus. Our upper peripheral visual field stimulus enabled us to distinguish V6 from neighbouring areas, whose upper VF representation is located far from V6. We recorded neuromagnetic signals while the subjects (N=10) fixated and a grating first appeared and then started to drift. The most prominent sustained activation for motion was at the posterior bank of the dorsal parieto-occipital sulcus; that is at the known location of the human V6. This finding suggests that human V6 is a motion-sensitive area. The responses in V6 occurred early, with about the same latency as in V1, in line with known connections in the monkey brain. In addition, on the medial surface of the hemisphere we observed a fast sequence of activations following V6: first precuneus and later an area at the dorsal end of the cingulate sulcus. On the lateral side, both temporo-occipital area and intraparietal sulcus were active, but with delayed onset compared to V6. This rapid flow of visual information along the medial dorsal visual pathway supports the view that in humans, as in monkeys, the V6 and the connected areas could be involved in online control of visually guided actions.