Spatiotemporal imaging of the brain activities during 3-D structure perception from motion

Here, we used both MEG and fMRI to detect dynamic brain responses to 3-D structure perception from random-dot motion in humans. The visual stimuli consisted of 1000 random dots, which started to move 500 ms after the onset of presentation. The coherence of the motion was controlled from 0 to 100%. A stimulus that is fully coherent had all the dots moving as if they belonged to a rotating spherical surface. On the other hand, the 80, 60, 40, 20, and 0% coherence stimuli contain dots having the same speed as the fully coherent stimuli, but the directions of the 20, 40, 60, 80, and 100% of the dots were randomized, respectively. Neuromagnetic signals were measured with a 306-channel MEG system. More than 60 stimulus-related epochs of 2000 ms, including a 1000 ms pre-stimulus baseline, were recorded and averaged for each condition with a sampling rate of 600 Hz. FMRI experiments were conducted using a 3 Tesla scanner covering the entire brain using blocked design, in which 12 s blocks were presented in pseudo-randomized order. The results of the fMRI analysis were used to impose plausible constraints on the MEG inverse calculation using a “weighted” minimum-norm approach to improve spatial resolution of the spatiotemporal activity estimates. The bilateral occipito-temporal and the intra-parietal regions showed increased neural activity in the fully coherent motion condition around the latencies of 180 ms and 240 ms after the onset of motion, respectively. These results indicate that the bilateral occipito-temporal and intra-parietal regions play an important role in the perception of 3-D structure from random-dot motion. Also, the present study adds further insight into the temporal characteristics of the neural activities in these regions.