1NIH, Bethesda, MD, United States; 2National Institutes of Health, Bethesda, MD, United States
How to extract specific neural information from fMRI signal remains challenging. Here, we demonstrate that fMRI onset laminar positions coincide with input neural projections in the cortex. Ascending thalamocortical input leads to fMRI onset at layer 4 and activation in motor cortex through somatomotor corticocortical connections shifts fMRI onset to layer 2/3 and 5. Following unilateral infraorbital denervation, ipsilateral fMRI activation in the deafferented barrel cortex to spared whisker input has an onset at layer 2/3 and 5, consistent with corticocortical callosal projections. This indicates that fMRI onset times may enable distinguishing thalamocortical (bottom-up) from corticocortical (top-down) inputs into cortex.