Phasic events, cyclic alternating pattern (CAP) and sleep disorders

Intermittent alpha rhythm, transient vertex sharp potentials, K-complexes, spindles, arousals, delta bursts, polyphasic bursts, sawtooth waves, muscle twitches, slow and rapid eye movements are distinct phasic events that occur throughout different sleep stages. During NREM sleep, arousal-related phasic events tend to aggregate into the ordered sequences of cyclic alternating pattern (CAP), which keeps the sleeping brain under control and provides a continuous balance between the programming centers (order) and the contingent psychological, organic and environmental factors (chaos). Due to its functional properties, CAP translates a condition of criticality and undergoes specific alterations in most sleep pathologies. The clinical applications of CAP are explored in sleep apnea syndrome, insomnia, narcolepsy, epilepsy, NREM and REM sleep parasomnias, as well as the involvement of CAP in cognitive processes and in critical care settings. During NREM sleep, the locus coeruleus (LC) exhibits infra-slow oscillatory activity with a periodicity that partially overlaps with that of CAP, suggesting a functional interaction between LC-driven noradrenergic rhythms and CAP dynamics. Through the structured collection of phasic events, CAP regulates sleep continuity, modulates responsiveness to internal and external stimuli and plays a coordinated activity in NREM sleep oscillations.