Returning Consciousness: Deeper Insights into Brain Transitions, Recovery, and Awakening

Flora Liu, MD

Anesthesiologists work with transitions of consciousness every day, yet the underlying brain circuitry, the effects of anesthetic and the mechanisms governing return to consciousness remain incompletely understood. “Transitions in Consciousness: Current Insights from the Anesthetized State,” co‑sponsored by the Society for Neuroscience in Anesthesiology and Critical Care (SNACC), was held on May 3, 2026, and brought together investigators using anesthesia as a powerful experimental tool to probe the neural basis of consciousness. Moderated by Ken Solt, MD, Edward Mallinckrodt Jr. associate professor of anaesthesia at Harvard Medical School and vice chair of research in the Department of Anesthesiology at Mass General Brigham, the session explored how anesthetics alter brain dynamics, how consciousness can fluctuate independently of drug dose, and how these insights may translate to improved monitoring and prognostication in perioperative and critical care settings.

Andrew McKinstry‑Wu, MD, PhD, an anesthesiologist and neuroscientist at the University of Pennsylvania, opened the session with “Extracting the Signal from the Noise: Separating Changes in Consciousness from Pharmacologic Effects,” exploring how anesthesiologists have a unique window into the biology of consciousness through the ability to induce unconsciousness on demand. A central challenge is that anesthetic drugs strongly shape neural signals, making it difficult to disentangle pharmacologic effects from the neural correlates of consciousness itself. Prior studies have demonstrated that sensory disconnection and unconsciousness arise from distinct neural mechanisms, and that EEG features such as slow‑wave and alpha‑band activity can help differentiate between states of consciousness.

Dr. McKinstry‑Wu achieved a steady‑state anesthesia designed to isolate fluctuations in consciousness independent of changing drug concentration. Xenon, a radiopaque anesthetic gas, enabled noninvasive measurement of brain anesthetic concentration using serial CT imaging. By confirming stable drug levels while recording EEG and behavioral responses during a Go/No‑Go task, the neural activity was recorded during spontaneous transitions between responsiveness and unresponsiveness. Results from the EEG markers demonstrate that both frontal peak alpha and dynamic criticality, which is a reflection on how neural activity responds to perturbation, did not show significant difference between responsive and unresponsive states. In contrast, statistical criticality, describing how closely brain activity operates near a critical point between order and disorder, decreased during unresponsiveness and increased with return of consciousness, suggesting a promising EEG‑derived marker less confounded by drug effect.

Catherine Duclos, PhD, associate professor in the Department of Anesthesiology and Pain Medicine at the Université de Montréal, addressed how anesthetic responses can be used to assess consciousness and predict recovery in patients. She presented, “From Sedation to Stimulation: Exploring Propofol’s Role in Prognostication and Recovery in Coma and Disorders of Consciousness.” She introduced the Adaptive Reconfiguration Index (ARI), a translational EEG‑based metric designed to overcome the limitations of traditional behavioral assessments. ARI quantifies changes in network hubs and directed functional connectivity. Dr. Duclos found that brain-injured patients who demonstrate coherent network reconfiguration under propofol retain the capacity to recover consciousness.

Interestingly, propofol does not uniformly suppress neural dynamics in patients with disorders of consciousness. Some individuals exhibit paradoxical markers of consciousness. These findings align with the criticality hypothesis, which proposes that the healthy conscious brain operates near a critical point between order and disorder, while anesthesia typically shifts the brain into a subcritical state. Paradoxical responses may arise from destabilization of the mesocircuit, where loss of striatal inhibition of the globus pallidus interna leads to excessive thalamic inhibition. In this context, GABAergic agents may paradoxically facilitate network reorganization in injured brains. Spectral analyses show heterogeneous responses to propofol, underscoring that anesthetic effects on consciousness are not one size fits all and may ultimately depend on baseline network state, injury location, or genetic factors.

As patients return to consciousness, anesthesiologists typically assess through verbal command-following, yet the neural circuits underlying this transition remain incompletely understood. Paola Calderon, MD, PhD, assistant professor of neuroscience in anesthesiology at Weill Cornell Medical College, presented “Unveiling Arousal States through Motor Behavior: Analysis of Premotor Cortices Dynamics During Reflexive and Volitional Behaviors,” highlighting how motor behavior may provide a more nuanced window into arousal and consciousness. Building on prior work showing that pharmacologic activation of neurons in the medullary reticular formation can restore arousal during deep anesthesia, Dr. Calderon demonstrated that these arousal centers recruit multiple ascending pathways and coordinate widespread cortical activation.

Dr. Calderon showed that reflexive movements were accompanied by minimal anterior lateral motor cortex (ALM) activation, whereas voluntary, goal‑directed behaviors produced marked increases in ALM activity, particularly within superficial cortical layers critical for communication and motor planning. She introduced the concept of “arousal units,” integrated cortical patterns linking motor behavior, autonomic changes, and EEG dynamics during emergence from anesthesia. Further work can translate these findings to humans, with the goal of developing reproducible and clinically meaningful markers of consciousness recovery in the operating room, PACU, and ICU.