Characterizing top-down microcircuitry of complex human behavior across different levels of the visual hierarchy

Abstract

FMRI has become a key tool for human neuroscience. At ultra-high field (=> 7 Tesla) it is possible to acquire images with submillimeter spatial precision, which allows examinations of mesoscale functional organization. Studying the brain at this scale does not come without its challenges, however. To tackle some of these challenges, we propose an approach that builds upon task modulations to identical visual stimuli and the simultaneous imaging of distal areas of varying complexity across the cortical hierarchy. Specifically, we record BOLD responses elicited by face stimuli during a stimulus relevant and a stimulus irrelevant task across cortical depths in V1, Occipital Face (OFA) and Fusiform Face area (FFA). We observed that task-related top-down modulations were larger in the inner compared to the outer layers of V1; and in the outer compared to the inner layers in the FFA. Our findings are consistent with animal reports of feedback exchange between deeper and superficial layers and with the notion of apical dendritic amplification as a key mechanism of conscious perception. Our approach showcases the potential of "laminar-fMRI" to explore large scale network activity and represents a promising step towards characterizing laminar functional profiles in humans for complex, cognitively meaningful, and socially relevant stimuli such as faces.