Supramarginal Gyrus Research Papers - Academia.edu (original) (raw)

Saccades change eye position and interrupt vision several times per second, necessitating neural mechanisms for continuous perception of object identity, orientation, and location. Neuroimaging studies suggest that occipital and parietal cortex play complementary roles for transsaccadic perception of intrinsic versus extrinsic spatial properties, e.g., dorsomedial occipital cortex (cuneus) is sensitive to changes in spatial frequency, whereas the supramarginal gyrus (SMG) is modulated by changes in object orientation. Based on this, we hypothesized that both structures would be recruited to simultaneously monitor object identity and orientation across saccades. To test this, we merged two previous neuroimaging protocols: 21 participants viewed a 2D object and then, after sustained fixation or a saccade, judged whether the shape or orientation of the represented object changed. We, then, performed a bilateral region-of-interest analysis on identified cuneus and SMG sites. As hypothesized, cuneus showed both saccade and feature (i.e., object orientation vs. shape change) modulations, and right SMG showed saccade-feature interactions. Further, the cuneus activity time course correlated with several other cortical saccade/visual areas, suggesting a 'functional network' for feature discrimination. These results confirm the involvement of occipital/parietal cortex in transsaccadic vision and support complementary roles in spatial versus identity updating. The ability to extract pertinent visual information from our surroundings depends on the brain's ability to aim, and account for, eye position 1-3. Rapid eye movements (saccades) help gather new visual information by aligning the fovea with objects of interest, at the cost of disrupting visual stability and memory by displacing the retinal image relative to the world 4,5. This necessitates some neural mechanism to continuously track both intrinsic object properties-cues to identity-and extrinsic spatial properties, like object location and orientation 5-8. It is thought that during saccades, oculomotor signals are used to 'update' retinal location 9-15 and other visual features 5,7. Recently, it has been shown that parietal and occipital cortex are involved in transsaccadic memory of object orientation and spatial frequency, respectively 16-18. However, in real world conditions, the brain must track intrinsic and extrinsic object properties simultaneously 19,20. Various structures in the occipito-parieto-frontal stream have been implicated in the spatial aspects of transsaccadic vision, notably the parietal and frontal eye fields 9,10,21-26. Likewise, transcranial magnetic stimulation (TMS) over various occipital, parietal, and frontal sites disrupts transsaccadic updating of object orientation 8,27-29. More recently, we employed functional magnetic resonance imaging (fMRI) adaptation 30,31 to identify areas that are specifically involved in transsaccadic comparisons of object orientation. These experiments identified an area in the right supramarginal gyrus (SMG), anterolateral to the parietal eye fields, that showed transsaccadic (object) orientation processing for both perception and grasp 16,17. It has proven more difficult to localize the cortical mechanisms that update features related to object identity 32. Modest amounts of feature remapping have been observed in monkey parietal eye fields 33. A recent human study has shown that stimulus features (specifically, spatial frequency) can be decoded from whole-brain magnetoencephalography signals after an intervening saccade 34. When we adapted our transsaccadic fMRI adaption