Optical Cortico-Cortical Evoked Potentials Reveal Structural and State-Dependent Cortical Communication

Background Cortico-cortical evoked potentials probe causal cortical communication in humans; however, establishing a preclinical methodological counterpart that combines cortex-wide coverage, high temporal resolution, minimal invasiveness, and awake-state recording remains challenging.Objective To map causal cortical communication and determine how local excitability, anatomical connectivity, and brain state jointly shape signal propagation across the cortex.Methods We used an all-optical platform that combines single-pulse transcranial optogenetic stimulation with widefield calcium imaging in awake mice, enabling stimulation and recording of cortex-wide responses from multiple motor, sensory, and association areas. We then related the spatiotemporal structure of these responses to local excitability, mesoscale functional organization, anatomical projection strength, and graded anesthesia.Results Optical Cortico-Cortical Evoked Potentials uncovered a consistent two-stage pattern of cortical communication. An initial response propagated along the anatomical scaffold linking the stimulated site to its direct targets, indicating that structural connectivity constrains the earliest phase of signal transmission. This was followed by a later, more distributed phase that varied across stimulation sites and was more sensitive to brain state, consistent with recurrent network-level integration. Across regions, stronger local recruitment was associated with broader cortex-wide engagement, suggesting that local excitability helps govern the scale of effective connectivity.Conclusions These findings establish oCCEPs as a scalable approach for causal mapping of cortical dynamics and support a two-stage principle of cortical communication: an early structurally constrained phase followed by a later state-dependent integrative phase.