Neurophysiology of Symmetry Processing in Macaque Visual Cortex

In a world composed of inherent regularities, symmetry intricately shapes spatial relationships, guiding visual scene organization. As a highly salient visual feature, the perception of symmetry properties has been demonstrated in different species, notably in the support of object recognition and figure-ground segregation. While the cortical network underlying symmetry processing has been extensively studied and identified in humans, functional imaging of this network in non-human primates (NHPs) has been limited to a single recent study (Audurier et al., 2021). Using fundamental symmetry stimuli generated from wallpaper type textures this study revealed a comparable rotational symmetry processing network between humans and NHPs that recruits cortical areas beyond V1, including V2, V3, V3A, and V4. To deepen our understanding of the neural responses to symmetry, we applied a dual approach combining intrinsic optical imaging (IOI) and multisite neurophysiology of primary visual cortical areas. IOI recordings were performed in anesthetized rhesus macaques in hopes of revealing symmetry selective domains at the mesoscale and to identify functional domains (e.g. orientation and color) for the functional targeting of electrodes. Subsequently, multi-site linear electrodes were implanted in V1, V2, V3, and V4 to assess the roles and dynamics among these distinct visual areas to the encoding of different symmetry conditions. Analyses of raster plots have revealed a subset of neurons that differentially encode rotational symmetry with there being potentially a greater proportion of such neurons in V4 and V2 than V3 and V1. This finding supports previous findings. Our integrative methodology aims to unravel the intricacies of symmetry processing and contribute to a more comprehensive understanding of visual perception of primates.