Characterization of Vertex Sharp Waves: Sleep Stage Distribution Pattern and Implications for Scoring

Study ObjectivesVertex sharp waves(VSW) are sharply contoured waves with a duration of less than 500 mille-seconds and maximal over the central regions of the brain, that have been identified to appear during N1. Here we postulate that VSW are sleep stage-specific and can also identify a sleep stage shift to NREM sleep from REM sleep.MethodsWe retrospectively analyzed PSG data of 20 out of 74 consecutive patients who were studied with 18-channel EEG within the last year. Vertex sharp waves were visually and manually scored and analyzed by sleep stage.ResultsTwenty patients(12 men, 60.0%) were analyzed. The median age was 37 years(95% CI 31.3-46.2 years) with a mean of 38.7 ± 14.4 years. Seventeen patients(85%) had VSW in both N1 and N2 sleep stage, only 6 patients(30%) had VSW in N3 sleep, and 10 patients(50%) in REM sleep. Regression analysis showed that the occurrence of VSW in N2 sleep(r² = 0.747,F = 44.366;p < 0.001) and REM sleep(r² = 0.473,F = 7.174; p = 0.028) was positively correlated with the presence of VSW in N1 sleep stage. The positive correlation during REM sleep was only spared for the VSW appearing following an arousal reaction(r² = 0.432, F = 5.329;p = 0.05).ConclusionsOur results suggest that vertex sharp waves are state-dependent activities of NREM sleep, predominantly seen in N1 sleep stage, and also in N2 sleep. As they emerge in REM sleep, following an arousal reaction or not, it may be regarded as a sleep stage shift from REM to NREM sleep stage. These findings may help clarify scoring rules for REM sleep and arousal.