Altered parasympathetic activity during sleep and emotionally arousing wakefulness in frequent nightmare recallers

People who frequently recall nightmares show signs of dysfunctional parasympathetic regulation during sleep and in response to emotional distress. Compared to healthy controls, nightmare recallers had higher heart rates during sleep segments (pre-REM, REM, post-REM, and slow wave sleep), but not during resting wakefulness, suggesting autonomic dysregulation specific to sleep. Heart rate variability did not differ significantly between groups during sleep, implying that parasympathetic changes may depend on nightmare severity. During an emotion-evoking picture-rating task designed to model nightmare experiences, nightmare recallers showed increased heart rate and reduced heart rate variability, indicating disrupted emotion regulation under acute distress. These findings point to both trait-like autonomic changes during sleep and state-like responses to emotional challenges.

Study at a glance

Abstract

Nightmare disorder is characterized by dysfunctional emotion regulation and poor subjective sleep quality reflected in pathophysiological features such as abnormal arousal processes and sympathetic influences. Dysfunctional parasympathetic regulation, especially before and during rapid eye movement (REM) phases, is assumed to alter heart rate (HR) and its variability (HRV) of frequent nightmare recallers (NM). We hypothesized that cardiac variability is attenuated in NMs as opposed to healthy controls (CTL) during sleep, pre-sleep wakefulness and under an emotion-evoking picture-rating task. Based on the polysomnographic recordings of 24 NM and 30 CTL participants, we examined HRV during pre-REM, REM, post-REM and slow wave sleep, separately. Additionally, electrocardiographic recordings of resting state before sleep onset and under an emotionally challenging picture-rating task were also analyzed. Applying repeated measures analysis of variance (rmANOVA), a significant difference was found in the HR of NMs and CTLs during nocturnal segments but not during resting wakefulness, suggesting autonomic dysregulation, specifically during sleep in NMs. As opposed to the HR, the HRV values were not significantly different in the rmANOVA in the two groups, implying that the extent of parasympathetic dysregulation on a trait level might depend on the severeness of dysphoric dreaming. Nonetheless, in the group comparisons, the NM group showed increased HR and reduced HRV during the emotion-evoking picture-rating task, which aimed to model the nightmare experience in the daytime, indicating disrupted emotion regulation in NMs under acute distress. In conclusion, trait-like autonomic changes during sleep and state-like autonomic responses to emotion-evoking pictures indicate parasympathetic dysregulation in NMs.