A Week in the Life of the Human Brain: Stable States Punctuated by Chaotic-Like Transitions.

Critical neurocognitive processes, such as performing natural activities and fluctuations of arousal, take place over minutes-to-days in real-world environments. Here we harness the opportunity to study brain dynamics during real-world behavior continuously for 3-12 days using multi-electrode intracranial recordings in twenty humans. During this time, participants engaged in natural activities, including interacting with friends, family, and staff, watching TV, sleeping, etc., with simultaneous neural and video recordings. We found that brain network dynamics predicted neurocognitive phenomena such as circadian rhythm, arousal, and multiple aspects of behavior (socializing, watching a screen, etc.). The individual functional networks, as well as their pairwise interactions, possessed simple and stable dynamic properties that were conserved over days. In contrast to single or paired network behavior, the mixture of all functional networks showed patterns of "punctuated equilibrium": periods where networks would remain in stable states that corresponded to behavior and were interrupted by transitory bursts that were difficult to predict, displayed chaotic characteristics, and coincided with behavioral transitions. Brain state statistics displayed power laws characteristic of critical dynamics that are a trait of systems where complexity emerges from simple and stable building blocks. These results indicate that the complex and flexible brain dynamics that underpin real-world behavior are an emergent property of mixtures of individual, stable networks with simple dynamics.