Main trends in rectal temperature during sleep. Hypnogram and thermogram

The Inconsistent Nature of Heart Rate Variability During Sleep in Normal Children and Adolescents

Introduction: Cardiac function is modulated by multiple factors including exogenous (circadian rhythm) and endogenous (ultradian 90–110 min sleep cycle) factors. By evaluating heart rate variability (HRV) during sleep, we will better understand their influence on cardiac activity. The aim of this study was to evaluate HRV in the dark phase of the circadian rhythm during sleep in healthy children and adolescents.

Methods: One 3 min segment of pre-sleep electrocardiography (EEG) and 3, 6 min segments of electrocardiography recorded during polysomnography from 75 healthy children and adolescents were sampled during progressive cycles of slow wave sleep (SWS1, SWS2, SWS3). Three, 3 min segments of rapid eye movement sleep (REM) were also assessed, with REM1 marked at the last REM period before awakening. Studies that recorded REM3 prior to SWS3 were used for assessment. HRV variables include the following time domain values: mean NN (average RR intervals over given time), SDNN (Standard Deviation of RR intervals), and RMSSD (root Mean Square of beat-to-beat Differences). Frequency domain values include: low frequency (LF), high frequency (HF), and LF:HF.

Results: Mixed linear effects model analysis revealed a significant difference in time and frequency domain values between sleep cycles and stages. Mean NN was lowest (highest heart rate) during pre—sleep then significantly increased across SWS1-3. Mean NN in SWS1 was similar to all REM periods which was significantly lower than both SWS2 and SWS3. SDNN remained at pre-sleep levels until SWS3, and then significantly increased in REM1&2. There was a large drop in LF from pre-sleep to SWS1. As cycles progressed through the night, LF remains lower than awake but increases to awake like levels by REM2. RMSSD and HF were lowest in pre-sleep and increased significantly by SWS1 and remain high and stable across stages and cycles except during the REM3 period where RMSSD decreased.

Conclusion: Our results demonstrate that there are considerable changes in the spectral analysis of cardiac function occurring during different sleep stages and between sleep cycles across the night. Hence, time of night and sleep stage need to be considered when reporting any HRV differences.

Heat Synch: Inter- and Independence of Body-Temperature Fluctuations and Brain-State Alternations in Urethane-Anesthetized Rats

During sleep, warm-blooded animals exhibit cyclic alternations between rapid-eye-movement (REM) and nonrapid-eye-movement (non-REM) states, characterized by distinct patterns of brain activity apparent in electroencephalographic (EEG) recordings coupled with corresponding changes in physiological measures, including body temperature. Recently we have shown that urethane-anesthetized rats display cyclic alternations between an activated state and a deactivated state that are highly similar in both EEG and physiological characteristics to REM and non-REM sleep states, respectively. Here, using intracranial local field potential recordings from urethane-anesthetized rats, we show that brain-state alternations were correlated to core temperature fluctuations induced using a feedback-controlled heating system. Activated (REM-like) states predominated during the rising phase of the temperature cycle, whereas deactivated (non-REM-like) states predominated during the falling phase. Brain-state alternations persisted following the elimination of core temperature fluctuations by the use of a constant heating protocol, but the timing and rhythmicity of state alternations were altered. In contrast, thermal fluctuations applied to the ventral surface (and especially the scrotum) of rats in the absence or independently of core temperature fluctuations appeared to induce brain-state alternations. Heating brought about activated patterns, whereas cooling produced deactivated patterns. This shows that although alternations of sleeplike brain states under urethane anesthesia can be independent of imposed temperature variations, they can also be entrained through the activation of peripheral thermoreceptors. Overall, these results imply that brain state and bodily metabolism are highly related during unconsciousness and that the brain mechanisms underlying sleep cycling and thermoregulation likely represent independent, yet coupled oscillators.

The decade 1989-1998 in Spanish psychology: an analysis of research in psychobiology

In this paper, we present an analysis of the research published during the 1989-1998 decade by tenured Spanish faculty members from the area of psychobiology. Database search and direct correspondence with the 110 faculty members rendered a list of 904 psychobiological papers. Classification and analysis of these papers led to the definition of at least 70 different research trends. Topics are grouped into several specific research areas: Learning and Memory; Development and Neural Plasticity; Emotion and Stress; Ethology; Neuropsychology; Sensory Processing; and Psychopharmacology. The international dissemination of this research, published in journals of high impact index, and the increasing number of papers are two noteworthy features.

A persistent circhoral ultradian rhythm is identified in human core temperature

There have been inconclusive reports of intermittent rhythmic fluctuations in human core temperature, with the fluctuations having a period of about an hour. However, there has been no definitive demonstration of the phenomenon. This is likely due to the intermittency and seeming instability of the events. They have been assumed to be secondary rather than autonomous phenomena, putatively arising from the oscillation between rapid eye movement (REM) and non-REM (NREM) sleep. In this study, we report identification of a clear, persistent circhoral ultradian rhythm in core temperature with a period for this study sample of 64 +/- 8 minutes. It appeared simultaneously with an intact circadian core temperature rhythm, persisted despite complex perturbations in core temperature brought about by the sequelae of 40 h of sleep deprivation, and could not be attributed to sleep stage alternation or other endogenous or exogenous factors. Analysis of power spectra using the maximum entropy spectral analysis (MESA) method, which can uncover hidden rhythmicities, demonstrated that the apparent intermittency of the rhythm is due to periodic interference of this rhythm by other rhythmic events. The persistence of this oscillation suggests that, in this system as in the endocrine system, circhoral regulation is an integral component of thermoregulatory control. Identifying the source and functional role of this novel rhythm warrants further work.