  The cognitive functions of human and non-human primates rely on the dynamic
interplay of distributed neural assemblies. As such, it seems unlikely that
cognition can be supported by macroscopic brain dynamics at the proximity of
thermodynamic equilibrium. We confirmed this hypothesis by investigating
electrocorticography data from non human primates undergoing different states
of unconsciousness (sleep, and anesthesia with propofol, ketamine, and ketamine
plus medetomidine), and funcional magnetic resonance imaging data from humans,
both during deep sleep and under propofol anesthesia. Systematically, all
states of reduced consciousness unfolded at higher proximity to equilibrium
dynamics than conscious wakefulness, as demonstrated by entropy production and
the curl of probability flux in phase space. Our results establish
non-equilibrium macroscopic brain dynamics as a robust signature of
consciousness, opening the way for the characterization of cognition and
awareness using tools from statistical mechanics.
