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Daniela Baslev, Tanja Kassuba; Gaze position-dependent modulation of the primary visual cortex from the eye proprioceptive representation – an offline TMS-fMRI study. Journal of Vision 2010;10(7):100. doi: 10.1167/10.7.100.
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Planned eye movements produce involuntary shifts in attention. The recent discovery of a proprioceptive eye position signal in the somatosensory cortex (Wang&al., 2007; Balslev&Miall, 2008) prompts the question whether static eye position, too, can affect visual attention. TMS over the left somatosensory cortex targets the eye proprioceptive representation, causing an underestimation of the gaze angle of the right eye (Balslev&Miall, 2008) and a pseudo-neglect for visual targets presented far versus near the perceived direction of gaze despite their equal retinal eccentricity. Namely when right eye was rotated leftwards and TMS shifted perceived eye position rightwards, visual detection increased in the right visual field and decreased in the left. When the right eye was rotated rightwards and TMS assumingly produced an underestimation of this rotation shifting perceived eye position leftwards, visual detection decreased in the right hemifield (Balslev, Gowen&Miall, unpublished). Here we used fMRI before and after rTMS over the left somatosensory cortex or motor cortex control area to investigate whether the eye proprioceptive representation is functionally connected to the visual cortex. Participants (n=11) fixated their right eye on a cross located on the screen at either to the left or right of the sagittal plane through the right eye. Visual targets appeared to the left or right of fixation at equal retinal eccentricity. In line with our behavioral results, somatosensory TMS significantly increased neural activity in a right parieto-occipital cluster (cluster p<0.05, corrected) in response to visual targets presented near vs. far the perceived direction of gaze. The peak voxel of this cluster was in Brodmann's area 17/18. This change in activity was specific for somatosensory TMS and was not found after TMS over a motor cortex control area. We suggest that static eye position signal influences the spatial distribution of visual processing resources by modulating visual cortex activity.
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