  Consciousness is supported by complex patterns of brain activity which are
indicative of irreversible non-equilibrium dynamics. While the framework of
stochastic thermodynamics has facilitated the understanding of physical systems
of this kind, its application to infer the level of consciousness from
empirical data remains elusive. We faced this challenge by calculating entropy
production in a multivariate Ornstein-Uhlenbeck process fitted to fMRI brain
activity recordings. To test this approach, we focused on the transition from
wakefulness to deep sleep, revealing a monotonous relationship between entropy
production and the level of consciousness. Our results constitute robust
signatures of consciousness while also advancing our understanding of the link
between consciousness and complexity from the fundamental perspective of
statistical physics.
