Taylor L. Li¹, Andrew S. Persichetti¹, Sam Audrain¹, Jiayu Shao¹, Laurentius Huber¹, Alex Martin¹; ¹NIMH (National Institute of Mental Health)

Layer-specific fMRI promises to dissociate feedforward and feedback information across cortical laminae from V1 to downstream category-selective visual regions in ventral occipitotemporal cortex (VOTC). However, using a cutting-edge functional MRI method called vascular space occupancy (VASO) to measure fMRI signals at submillimeter resolution comes with major methodological challenges. Thus, we introduce two methodological advances that allow us to measure layer-specific fMRI signals in VOTC. The first is a forward model that can predict the optimal flip angle regime for the VASO sequence in the brain region to be studied. The second is an anatomical segmentation routine that cleanly segments the cortical ribbon from white matter and cerebral spinal fluid for precise definition of cortical layers. We used this optimized VASO fMRI routine in a study on perceving and imaging faces and places. Participants saw the names of famous faces and places followed by either a picture (perception), or a white frame (mental imagery) during separate task blocks. After independently localizing the fusiform face area and parahippocampal place area, we found preliminary evidence that mental imagery elicits the strongest responses in the superficial and deep layers of the corresponding category-selective region that receive feedback signals from higher-order brain regions but not in the middle layers that receive feedforward signals from early visual cortex. In contrast, viewing pictures of famous faces and places elicits the strongest responses in the middle (and superficial) layers. Thus, our methodological advances allow us to accurately dissociate feedforward and feedback information across layers of VOTC.