Scalp EEG and Intrinsic Optical Signal Imaging for Noninvasive Detection of Spreading Depolarizations in the Rat Cortex.

Spreading depolarization (SD) is a slowly propagating wave of massive neuronal and glial depolarization in the cerebral cortex that occurs in various brain diseases. However, noninvasive SD detection remains challenging. Here, we used scalp EEG and intrinsic optical signal (IOS) recordings in rats of both sexes to assess the feasibility of noninvasively detecting high-potassium-induced SDs in the cortex. Scalp EEG failed to detect DC-shifts but revealed a characteristic SD-related depression of AC-EEG activity, while concurrent infrared IOS recordings captured reliable SD-associated signals. Although the magnitudes of AC-EEG depression and IOS signals during scalp recordings were several times smaller than those recorded epidurally, both techniques enabled high-fidelity SD detection. These findings demonstrate that noninvasive monitoring of scalp EEG and infrared IOS imaging reliably detects SDs in the rat cerebral cortex.