Cortico-cortical evoked hemodynamic responses in human language systems using intraoperative near-infrared spectroscopy during direct cortical stimulation

•We evaluated language system cortico-cortical networks with intraoperative NIRS.•Broca’s area was stimulated and recordings were made around Wernicke’s area.•50Hz stimulation elicited hemodynamic changes in the superior temporal gyrus.•This technique can aid intraoperative monitoring of the cortico-cortical networks. Understanding of cortico-cortical activity in eloquent areas intraoperatively is crucial for neurosurgical procedures. Here, we used intraoperative near-infrared spectroscopy (iNIRS) during direct cortical stimulation as a robust tool to better understand the cortico-cortical connectivity in language systems. We applied iNIRS to 3 patients who underwent epilepsy surgery due to lesions (cavernous angioma, epidermoid cyst, and low-grade glioma) located in language areas. Using iNIRS, we measured the blood concentration changes of oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR) in the lateral temporal cortex during direct cortical stimulation (50Hz) at the inferior frontal area where Broca’s area was probabilistically located. In all patients, 50Hz stimulation elicited hemodynamic changes in the superior temporal gyrus (STG). During 0.8–4.8s after stimulation, HbO2 increased and HbR decreased in the posterior part of the STG (Wernicke’s area). Similar responses were observed in the anterior part of the STG 1.3–8.0s after stimulation. Finally, these changes were disappeared in the middle temporal gyrus. Our results suggest that cortical stimulation of Broca’s area elicits hemodynamic responses in Wernicke's area via cortico-cortical connectivity. We demonstrated cortico-cortical evoked responses in language systems using iNIRS during direct cortical stimulation. Our iNIRS data will provide useful information about cortico-cortical networks underlying human brain functions intraoperatively and will contribute to neurosurgical treatment in eloquent areas.