By Davor Curic (University of Calgary, AB). November 8th, 2022.
Sleep dynamics have been described as a switching between two broad states; non-rapid eye movement sleep (nREM), which is associated with high delta power thought to originate from widespread neuronal synchronization, and REM, where-in neuronal desynchronization produces high theta power reminiscent of waking behavior. For a long time it was thought that REM and nREM constituted global brain states. However, recent research suggests that this is not true – spatio-temporally localized neuronal synchronization and desynchronization coexist, produced by complex neuronal dynamics during sleep. Here we utilize time-frequency analysis of mesoscopic voltage-sensitive dye recordings of mice to study avalanches of neuronal desynchronization, and how they evolve in space and time. We find that cortical synchrony and desynchrony co-exist, akin to a chimera state, with desynchronization avalanches statistics reminiscent of a critical spreading process, which has been theoretically theorized but not experimentally observed until now. This suggests an operating regime at an ‘edge-of-synchronization’ phase transition, re-framing the nREM-to-REM transition as a scale-free perturbation away from a synchronized absorbing state, as opposed to a global switching from one brain state to another. These results work towards connecting previously established concepts of neuronal avalanches, criticality and optimality, together with brain rhythms and synchronization.