Effective connectivity between homologous cortices mediated by the corpus callosum: An axono-cortical evoked potentials study

Objective: To demonstrate the role of the corpus callosum in interhemispheric effective connectivity and investigate the distribution of the connectivity originating from it using axono-cortical evoked potentials. Methods: A 14-year-old girl with drug-resistant focal epilepsy underwent total callosotomy. Intraoperatively, we placed four subdural strip electrode contacts on the corpus callosum and eight on each hemisphere. We applied single-pulse electrical stimulation to eight pairs of contacts placed on the corpus callosum and cerebral cortex, recording axono-cortical, cortico-axonal, and cortico-cortical evoked potentials. Propagation latencies and anatomical distributions were determined based on the first negative deflection within 10-50 ms. Results: Stimulation of the rostral to the anterior midbody elicited responses in bilateral anterior premotor cortices. The anterior to posterior midbody stimulation elicited responses in more posterior premotor cortices. The sum of latencies from the corpus callosum to each hemisphere (23.5 + 21.75 = 45.25 ms) approximated the interhemispheric neural propagation latency (44.5 ms). No significant responses were observed within the corpus callosum. Conclusion: The corpus callosum mediated effective connectivity between homologous cortices aligned along the anterior-posterior axis, consistent with known structural connectivity. Significance: This study provides the first direct neurophysiological evidence of the contribution of the corpus callosum to interhemispheric effective connectivity, highlighting its structural-functional correspondence and limitations in generating local field potentials.