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Abstract:
Mental imagery and veridical perception are two phenomenologically similar processes relying on largely overlapping neural substrates. However, both differ fundamentally in the underlying information flow. While perception results from the integration of bottom-up/feedforward and a top-down/feedback information, mental imagery lacks this bottom-up sweep. Here, we investigated the role of feedforward and feedback information flow in high-level category-selective regions during imagery and perception. For this, we relied on the layer-specificity of feedforward and feedback connections found in primate early visual cortex: feedforward projections terminate in middle layers and feedback projections arrive in superficial and deep layers. We recorded the BOLD activity from the fusiform face area (FFA) and the parahippocampal place area (PPA) using lamina-resolved fMRI, while participants (N=5) were shown and asked to imagine faces and places. Using multivariate analysis, we determined whether voxel patterns discriminate between faces and places for each laminar compartment (deep, middle and superficial), stimulus modality (perceived or imagined) and brain area (FFA and PPA). For both imagery and perception conditions, we found increased information from deep to superficial compartments in both FFA and PPA. Our results are consistent with a mental imagery model where feedback modulates lower visual regions, which then provide feedforward information to high-level visual areas.
