Laminar specific fMRI response is mainly regulated by first synaptic input-driven or more synchronous activity

Motivation: While responses to feedforward inputs have been well-observed in layer-specific fMRI studies, our understanding of responses to feedback projections within the ongoing functional processing remains limited. Goal(s): Our study aimed to investigate how synaptic onset and strength contribute to specificity of laminar fMRI responses. Approach: We performed the ultrahigh resolution CBV-weighted laminar fMRI by modulating thalamocortical and corticocortical projections with stimulus onset asynchrony in mice. Results: We observed that the laminar response is highly sensitive to the strength of synaptic inputs, shifting from early to later input sites with increased strength. Impact: Laminar CBV responses are highly regulated by micro-vessels coupled with earlier synaptic input activity, but potentially driven by the most synchronous activity within neural circuits.