This study investigated the effects of variations in sleep pressure on cardiac autonomic activity and body temperature. In a counterbalanced design, 12 healthy, young subjects (6 men and 6 women) remained recumbent during 30 h of wakefulness (high sleep pressure) and 6 h of wakefulness (low sleep pressure). Both periods of wakefulness were immediately followed by a sleep opportunity, and the first 2 h of sleep were analyzed. During extended hours of wakefulness, a reduction in heart rate was mediated by a decline in cardiac sympathetic activity (measured via preejection period) and the maintenance of cardiac parasympathetic activity (measured via respiratory sinus arrhythmia). In subsequent high-pressure sleep, parasympathetic activity was amplified and sympathetic activity was negatively associated with electroencephalographic slow-wave activity. Sleep deprivation had no impact on foot temperature, but it did alter the pattern of change in core body temperature. A downregulation of cardiac autonomic activity during both extended hours of wakefulness and subsequent sleep may respectively provide “protection” and “recovery” from the temporal extension of cardiac demand.

Melatonin increases sleepiness, decreases core temperature, and increases peripheral temperature in humans. Melatonin may produce these effects by activating peripheral receptors or altering autonomic activity. The latter hypothesis was investigated in 16 supine subjects. Three conditions were created by using bright light and exogenous melatonin: normal endogenous, suppressed, and pharmacological melatonin levels. Data during wakefulness from 1.5 h before to 2.5 h after each subject’s estimated melatonin onset (wake time + 14 h) were analyzed. Respiratory sinus arrhythmia (cardiac parasympathetic activity) and preejection period (cardiac sympathetic activity) did not vary among conditions. Pharmacological melatonin levels significantly decreased systolic blood pressure [5.75 ± 1.65 (SE) mmHg] but did not significantly change heart rate. Suppressed melatonin significantly increased rectal temperature (0.27 ± 0.06°C), decreased foot temperature (1.98 ± 0.70°C), and increased sleep onset latency (5.53 ± 1.87 min). Thus melatonin does not significantly alter cardiac autonomic activity and instead may bind to peripheral receptors in the vasculature and heart. Furthermore, increases in cardiac parasympathetic activity before normal nighttime sleep cannot be attributed to the concomitant increase in endogenous melatonin.

Objective: To compare noninvasive measures of cardiac autonomic activity during sleep. Methods: The absolute and normalized (n.u.) high and low frequency peaks from the spectral analysis of R-R intervals (HF, LF, HFn.u., LFn.u.), LF/HF ratio, pre-ejection period (PEP) from impedance cardiography, and the autocorrelation coefficient (rRR) as illustrated in Poincaré plots were measured during night-time sleep in 9 young healthy subjects. Heart rate and blood pressure were also recorded. Results: Heart rate was significantly associated with cardiac sympathetic activity (PEP, average r=−0.46), but not with cardiac parasympathetic activity (HF, average r=−0.17). rRR was significantly associated with heart rate (average r=0.41), and LF/HF (average r=0.69), but not with PEP or HF. From NREM to REM sleep, heart rate, LFn.u., LF and rRR significantly increased, HFn.u. significantly decreased, LF/HF showed an increasing trend (P=0.07) and PEP showed a decreasing trend (P=0.06). Blood pressure and HF were highly variable without significant changes from NREM to REM sleep. Conclusions: Cardiac parasympathetic activity (HF) does not vary greatly between sleep stages. Cardiac sympathetic activity (PEP) decreases linearly during sleep. rRR and LF/HF can track sympathovagal changes during sleep, but cannot differentiate between changes in cardiac parasympathetic and sympathetic activity. The relative advantages and disadvantages of the different measures are discussed.

It has been hypothesized that the ratio of heart rate variability in the low- (LF) and high- (HF) frequency bands may capture variation in cardiac sympathetic control. Here we tested the temporal stability of the LF/HF ratio in 24-h ambulatory recordings and compared this ratio to the preejection period (PEP), an established measure of cardiac sympathetic control. Good temporal stability was found across a period of 3.3 years (.46

Background: Patients suffering from dissociative disorders (DD) are characterized by an avoidance of aversive stimuli. Clinical experience has shown that DD patients typically avoid the confrontation with their own faces in a mirror (CFM).Objective: To investigate potential CFM-associated self-reported and psychophysiological stress reactions of DD patients, which most likely inform on the still unknown pathophysiology of dysfunctional self-perception in DD.Method: Eighteen DD patients and 18 healthy controls (HCs) underwent CFM. They were assessed for CFM-induced subjective self-reported stress, acute dissociative symptoms and sympathetic and parasympathetic drive using impedance cardiography.Results: DD patients experienced more subjective stress and acute dissociation than HCs upon CFM. Their psychological stress response did not activate the sympathetic and parasympathetic nervous system.Conclusions: In DD patients, CFM constitutes serious self-reported stress and is associated with a blunted autonomic reactivity. Therapeutic approaches promoting self-perception and self-compassion, in particular by using CFM, might serve as goal-oriented diagnostic and therapeutic tools in DD.

Mentalizing—the ability to understand and attribute mental states to others—relies on effective self-regulation and social-cognitive processing, both of which may be shaped by cardiac autonomic responses. While prior research has primarily emphasized the role of cardiac parasympathetic (PSNS) activity in social cognition, the contribution of cardiac sympathetic (SNS) activity and its dynamic interaction with PSNS remains underexplored. This study simultaneously investigated resting and task-related cardiac sympathetic-parasympathetic activity and reactivity to examine the associations with mentalizing performance in healthy young adults (N = 120). Resting heart rate variability and systolic time intervals were used to index cardiac PSNS and SNS activity, respectively, with phasic reactivity calculated as percentage change scores during mentalizing performance. Hierarchical regression analyses showed that higher cardiac PSNS activity and lower cardiac SNS activity at rest jointly predicted better mentalizing performance. Importantly, reduced cardiac SNS reactivity—but not cardiac PSNS reactivity—was a stronger predictor of mentalizing performance, and further mediated the relationship between resting cardiac autonomic activity and mentalizing performance. These findings highlighted the importance of cardiac SNS control, alongside cardiac PSNS control, in supporting socio-cognitive processing. This study suggested the understanding of efficient regulation to physiological arousal and advocated for an integrative cardiac psychophysiological model of social cognition that incorporates both cardiac sympathetic-parasympathetic branches.

Theory of mind (ToM) enables individuals to decode and attribute others’ mental states to predict their behavior. While cardiac autonomic activity, particularly cardiac parasympathetic (PSNS) activity, is linked to social cognition, most previous studies infer cardiac sympathetic (SNS) activity rather than examining both simultaneously. This study aimed to investigate both cardiac PSNS and SNS activities to provide a more comprehensive understanding of ToM ability in young adults. Cardiac PSNS and SNS activities were simultaneously measured at rest in 146 participants (mean age = 20.84, SD = 2.86 years) in a cross-sectional study, and in 73 of these participants (mean age = 21.56, SD = 2.70 years) 12 months later. ToM ability was assessed using the Chinese version of the Faux Pas Recognition Test. The results indicated significant uncoupled but reciprocal associations between ToM ability and both cardiac PSNS and SNS activities. Hierarchical regression analysis further revealed that higher cardiac PSNS activity and lower cardiac SNS activity together predicted better ToM ability and its cognitive component, after controlling for possible covariates. Preliminarily, a two-wave cross-lagged panel model demonstrated a significant inverse bidirectional relationship between cardiac SNS activity and ToM ability, along with a positive predictive relationship between ToM ability and cardiac PSNS activity 1 year later. In conclusion, the present study provides direct evidence for a relationship between ToM ability and the simultaneous combination of both cardiac PSNS and SNS activities in young adults. Notably, these findings suggest the possibility that cardiac SNS activity may play an equally important, if not more crucial, role in social-cognitive processes.