Multiscale dynamical characterization of cortical brain states: from synchrony to asynchrony

The cerebral cortex spontaneously displays different patterns of activity that evolve over time according to the brain state. Sleep, wakefulness, resting states, and attention are examples of a wide spectrum of physiological states that can be sustained by the same structural network. Furthermore, additional states are generated by drugs (e.g., different levels of anesthesia) or by pathological conditions (e.g., brain lesions, disorders of consciousness). While the significance of understanding brain states in relation to brain dynamics and behavior has become increasingly evident over the past two decades, a unified definition of brain states remains elusive. In this review, we focus on two extremes of this spectrum: synchronous versus asynchronous states. These functional states predominantly underlie unconsciousness and consciousness, respectively, although exceptions exist. Our aim is to integrate data from different levels into a multiscale understanding, ranging from local circuits to whole-brain dynamics, including properties such as cortical complexity, functional connectivity, synchronization, wave propagation, and excitatory-inhibitory balance that vary across states and characterize them. Experimental and clinical data, as well as computational models (at micro-, meso-, and macrocortical levels) associated with the discussed brain states, are made available to readers.