Contributed Talks III: At a glance - Facilitated identification of abnormal representations in the visual cortex with fMRI micro-probing

The integrity of visual function is based on the perfect match of retinal and post-retinal processing. Consequently, current therapeutic initiatives to restore the retinal input to the human visual system also require advanced functional imaging of the visual cortex. For this purpose, fMRI-based "micro-probing" [1] is of particular promise to visualize of population receptive field (pRF) abnormalities without a priori assumptions about their structure. This is here demonstrated for cortical representation abnormalities in a participant born without optic chiasm (achiasma), for whom fMRI-based pRF-mapping of the visual cortex at 3 Tesla was performed and micro-probing-based pRF structures were visualized as back projections into the visual field. Conventional analysis methods result in cortical maps ipsilateral to the stimulated eye that are difficult to interpret and that allow for predictions of the cortical organization only with specific a priori assumptions. Micro-probing, on the other hand, reveals "at a glance" abnormal, systematically fragmented pRFs that are mirror-symmetric along the vertical meridian (symmetry coefficient achiasma > controls (0.30 vs 0.03); p<0.001)). The micro-probing results directly demonstrate the predictions of previous achiasma studies and thus bear great potential of fMRI-based micro-probing to identify pathology-related, unknown representation abnormalities of the visual cortex. [1] Carvalho et al. (2020) Neuroimage 209:116423.