Figure 1.

Conceptual overview of cortical dynamics present during the sleep-wake cycle in the context of critical brain states. (A) Ascending pathways from the suprachiasmatic nucleus, hypothalamus, thalamus to cortex, where layers I—VI have been recently explored with respect to cortical dynamics. (B) The presence of offline periods of neuronal firing during NREM sleep and sleep deprivation. (C) Temporal autocorrelations of neuron firing reveal that slowly decaying functions are present during quiet wake and REM sleep, whereas fast decaying rates were found in NREM and sleep deprivation vigilance states. (D) Probability distributions have been used to characterize event scales vs. their frequency, e.g., neurons fired per second vs. log of neurons fired frequency. These distributions when tested against model likelihood functions such as power-laws, revealing universal scaling relationships that sits within a critical or subcritical regime. (E) Cortical activity can also be further characterized by partitioning fluctuations (e.g., EEG or LFP amplitudes) into a fixed hierarchy of duration bins and averaging these amplitudes to derive an average shape. These average shapes can be further renormalized to have a unit time and unit area to directly compare short and long time scales of cortical activity, e.g., average shapes at different durations that collapse on one another (red, green) indicate scaling functions consistent with criticality; however, if these average shapes differ from each other at different durations (magenta, blue) they may indicate deviations away from a critical system, an important consideration for addressing mechanisms of neuron firing and spatiotemporal activity during NREM, REM, quiet wake and sleep deprivation periods.