The Dynamics of (Un)Consciousness: Insights from Olfaction and Respiration

Abstract: Millions of people experience loss of consciousness after brain injury each year worldwide. The loss of consciousness could last seconds to years and, in some cases, for the rest of the person’s life. It is critical to know whether a brain-injured patient is conscious, minimally conscious, or unconscious to provide an accurate diagnosis and prognosis that guide rehabilitation and end-of-life decisions. Yet, despite this importance, standard behavioral methods for consciousness detection often fail, either because of sensory and motor deficits or due to the heterogeneous etiology and pathophysiology. There is therefore a pressing need for personalized diagnostic and prognostic tools that enable single-patient level assessment. Olfaction, which has a unique interaction with consciousness, offers a promising avenue for detecting covert consciousness. Building on this insight, we have developed innovative approaches that combine olfactory stimulation with physiological measures to probe residual awareness in patients with disorders of consciousness and reveal preserved processing that is not accessible through overt behavior, opening the door to more sensitive assessments and, ultimately, improved clinical care.