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Abstract:
Body motion is an indispensable source of information for social cognition and interaction. Yet display inversion severely impedes biological motion (BM) processing. The primary advantage of upside-down presentation is that an inverted display retains the same relational structure and absolute motion as an upright one, thereby keeping the same amount of sensory information available. This is why display inversion often serves as a control for proper BM processing in patients with neurodevelopmental, neurological and psychiatric disorders. It is still unclear how brain networks underpinning body motion processing are affected by display inversion. To address this issue, we used ultra-high field fMRI at 9.4T providing for highest spatial resolution and sensitivity in humans. Typically developing adults performed a two-alternative-forced-choice (2AFC) task, indicating whether an upright point-light walker or control displays (the same movies inverted 180 deg) were presented. An upright walker elicited most pronounced clusters of fMRI activity in the bilateral superior occipital cortices and the right middle temporal cortex, whereas the inverted display results in bilateral activity of lower occipital cortices, primarily, the lingual cortices and the left fusiform gyrus. Activation in these areas exhibited specific temporal dynamics: a decrease in activation in the second 5 s of stimulus duration, with a recurrent increase afterwards that presumably reflects back propagating influence. Most importantly, we uncovered pivots of activity in the distributed network driven by cognitive processing of the similar visual input: Perceivers who did not recognize upside-down displays as a walker exhibit several clusters of activity in the right hemisphere including the lingual, postcentral cortices, and the pars operculum. The outcome provides novel insights on the brain networks underlying BM processing and its functional neuroanatomy.
