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Abstract:
Introduction:
Body motion (BM) is a rich source of information for social cognition and interaction. Yet display inversion severely impedes 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 unclear whether and, if so, how brain circuits underpinning BM processing are affected by display inversion. As the visual displays are rather similar, inversion makes possible direct comparison of fine brain activation driven by cognitive processing of visual input. Yet previous functional magnetic resonance imaging (fMRI) studies, which used devices with magnetic field strength with limited spatial resolution, had been primarily restricted to analysis of activity in regions of interest (ROIs) being incapable to capture fine alterations in the whole-brain activity elicited by cognitive processing.
Methods:
Here we used ultra high fMRI at 9.4T equipped with whole-body gradients (Siemens Medical Systems, Erlangen, Germany) and a head-coil with a 16 channel dual row transmit array, and a 31 channel receive array operating in the circularly polarized transmit mode. The measurement protocol consisted of scout imaging, B0 shimming, mapping of B1, and adjustment based on flip angle values in cortical areas, anatomical imaging and acquisition of fMRI images. Healthy volunteers (25 paid right-handed males) were enrolled. As BOLD response in females is reported to fluctuate with menstrual cycles, for attaining a homogeneous BOLD signal, male volunteers only were recruited. In addition, sex differences are reported in both hemodynamic and neuromagnetic brain response to BM. In three runs, participants were presented with a set of 48 displays (2 orientations (upright/inverted) x 2 facing direction (right/left) x 4 times x 3 runs). They performed a two-alternative-forced-choice (2AFC) task indicating whether an upright point-light walker or control displays (the same movies inverted 180 deg in the image plane) were presented. Each stimulus appeared for 20 sec on a blank screen with an interstimulus interval of 16 sec. Prior to image segmentation, the MP2RAGE contrast images were corrected for deviations of the read-out flip angle and the inversion efficiency. Standard image segmentation and normalization into MNI space was then performed in SPM12. Functional MRI scanning was performed with a 3D EPI sequence with TR 1333 ms, TE 18 ms, isotropic voxel size 1.5 mm, and 8-fold acceleration. For each of three runs, a total of 450 images were acquired.
Results:
The outcome of the whole-brain analysis indicates that both upright and inverted BM displays elicit similar overall patterns of activaty with bilateral peaks in the primary and secondary areas of occipital cortices, inferior parietal cortices, precentral cortices, and in the right superior temporal gyrus and inferior frontal gyrus (p<0.001; FWE corrected). The upright walker as compared to upside-down presentation, elicits most pronounced clusters of fMRI activity in the bilateral extrastriate occipital cortices, whereas the opposite contrast results in bilateral activity in lower parts of the primary occipital cortices. Most intriguing, perceivers who did not recognize upside-down presentation as a walker and/or had several display interpretations (as compared with those who did recognize) exhibit activity in the distributed network with hubs in the right hemisphere including the lingual and precentral cortices.
Conclusions:
The outcome provides novel insights on the brain networks underlying body motion processing (as an essential part of the social brain) and its functional neuroanatomy. The findings offer the framework for studying neurobiology of neurological and psychiatric disorders.
