Dysfunction of inhibitory–excitatory cortical circuits induces density-dependent facilitation of motor-evoked potentials after subarachnoid hemorrhage

Intraoperative monitoring of motor-evoked potentials (MEPs) is important for preventing serious ischemic complications during aneurysm surgery following subarachnoid hemorrhage (SAH). Reduced intraoperative MEP amplitude indicates corticospinal tract neuronal damage, which should be avoided during surgical maneuvers. We aimed to investigate whether the MEP amplitude immediately before surgery can serve as both a control value for intraoperative MEP and an indicator of the pathophysiology of cortical excitability and inhibitory–facilitatory circuits immediately after SAH and neurological functional disturbance during the perioperative period. The present study focused on the MEP amplitude prior to intraoperative clipping and coil embolization and found that the MEP amplitude in the hemisphere with more significant SAH was significantly higher than that in the contralateral hemisphere. We also demonstrated that the MEP amplitude facilitation ratio significantly and linearly correlated with the initial computed tomography (CT) hematoma density [Hounsfield units (HU)] ( p < 0.0001). The MEP facilitation ratio linearly correlated with abnormalities in short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) values. Significant correlations were observed in the SICI and ICF groups with delayed cerebral ischemia ( p < 0.0001), whereas the ICF group showed a similar trend but weaker correlation ( p = 0.0732). A high MEP amplitude just before surgery correlates well with Sylvian fissure HU values on initial CT and may reflect dysfunction in the cortical electrophysiological intracortical inhibitory–facilitatory neuronal circuits of SAH.