Analogous cortical reorganization accompanies entry into states of reduced consciousness during anesthesia and sleep.

Theories of consciousness propose that brain mechanisms for losing and regaining consciousness are similar regardless of cause. Using intracranial electroencephalography in neurosurgical patients during propofol anesthesia and overnight sleep, researchers found strikingly similar reorganization of cortical networks. Effective dimensionality of functional connectivity decreased during reduced consciousness (anesthesia unresponsiveness, N2 and N3 sleep), indicating lower network complexity. These changes were global, not region-specific. Brain regions became more functionally distant yet individual recording sites closer to nearest neighbors, reflecting decreased differentiation and integration. This network reorganization constitutes a common neural signature of reduced consciousness across anesthesia and sleep, providing a framework for understanding neural correlates of consciousness.

Study at a glance

Abstract

Theories of consciousness suggest that brain mechanisms underlying transitions into and out of unconsciousness are conserved no matter the context or precipitating conditions. We compared signatures of these mechanisms using intracranial electroencephalography in neurosurgical patients during propofol anesthesia and overnight sleep and found strikingly similar reorganization of human cortical networks. We computed the "effective dimensionality" of the normalized resting state functional connectivity matrix to quantify network complexity. Effective dimensionality decreased during stages of reduced consciousness (anesthesia unresponsiveness, N2 and N3 sleep). These changes were not region-specific, suggesting global network reorganization. When connectivity data were embedded into a low-dimensional space in which proximity represents functional similarity, we observed greater distances between brain regions during stages of reduced consciousness, and individual recording sites became closer to their nearest neighbors. These changes corresponded to decreased differentiation and functional integration and correlated with decreases in effective dimensionality. This network reorganization constitutes a neural signature of states of reduced consciousness that is common to anesthesia and sleep. These results establish a framework for understanding the neural correlates of consciousness and for practical evaluation of loss and recovery of consciousness.