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Sleep state-dependent modulations of hippocampal theta oscillations and sharp wave-ripples by pontine waves

Ponto-geniculo-occipital (PGO) or pontine (P) waves are a prominent electrophysiological marker of rapid eye movement (REM) sleep. Although P-waves have long been recognized, they have been less studied compared to other sleep-related neural events. Recent studies in mice and macaques uncovered state-dependent functional coupling of P-waves with hippocampal oscillations, including sharp wave-ripples (SWRs) during non-REM (NREM) sleep and theta oscillations during REM sleep. However, the detailed characteristic of this functional coupling remains unclear. In addition, since P-waves in mice have been reported rarely, it is also important to describe their detailed electrophysiological properties, given the importance of the animal model. Here, we address these issues by performing multiple types of electrophysiological recordings in mice. P-waves characterized by diverse brainstem firing appear more frequently during REM sleep, and in both hemispheres at the same time across sleep states. The P-wave frequency can also predict the duration of REM sleep episodes. While P-waves induce modulated hippocampal excitability and phase coupling with theta oscillations during REM sleep, surprisingly P-waves lead to shorter SWRs during NREM sleep. These results suggest that P-waves play a role in systems memory consolidation by functionally coupling with hippocampal ensembles in a state-dependent fashion.