Synchronization between hippocampal theta waves and PGO waves during REM sleep

We investigated the temporal relationship between hippocampal theta waves (referred to as 'theta waves') and ponto-geniculo-occipital (PGO) waves in cats. We measured the time intervals between an occurrence of a PGO wave and the prior and posterior adjacent positive peaks of the theta wave. The unimodal distributions of these intervals suggested a close temporal relationship between PGO and theta waves (i.e. synchronization). In addition, the period of a theta wave during which a PGO wave occurred was not statistically different from that without a PGO wave. This result suggests that the synchronization found here is characterized by phase-locking rather than phase-resetting. Common mechanisms are suggested to underlie the generation of PGO and theta waves.