Dexmedetomidine (DEX) is a sedative that produces a sleep-like state and offers a way to study shifts in consciousness using behavior, EEG, and TMS-evoked EEG responses. Little is known about how repeated DEX exposure affects recovery. This pilot trial plans to sedate 12 healthy volunteers twice, one week apart, monitoring responsiveness with an auditory click task. It will compare time to return of responsiveness between visits, explore sex differences, and assess state transitions via EEG signatures, TMS-evoked complexity, and cognitive tests. The study also evaluates the feasibility of TMS-EEG during DEX sedation and reports on sleep quality and experiences.
Consciousness depends on both arousal (wakefulness) and awareness. While cortical networks for awareness are well studied, the subcortical networks supporting arousal are less understood. By combining ex vivo diffusion MRI, immunohistochemistry, and in vivo 7 Tesla functional MRI in three human brain specimens, the authors identified a default ascending arousal network (dAAN) in the brainstem, hypothalamus, thalamus, and basal forebrain. They mapped connections within the dAAN and between the dAAN and the cortical default mode network (DMN), suggesting a structural basis for integrating arousal and awareness. The data and methods are released to aid further mapping of human consciousness.