Interaction Between Body Temperatures and the Direction of Sleep Stage Transition in Neonates
Véronique Bach, Frédéric Telliez, André Leke, Carlo Chiorri, Jean-Pierre Libert

A cool environment increases active sleep (AS) of neonates at the expense of quiet sleep (QS). With regard to the interaction between thermoregulation and sleep, the aim of this study was to determine whether the levels and patterns of body temperatures differ between AS and QS, and according to the outcome of an AS episode (QS or wakefulness). This has never been studied in neonates. Thirty-seven neonates were exposed to a thermoneutral and a cool environment. Esophageal, mean skin temperature and oxygen consumption (Vo₂) were scored during AS and QS episodes and at the sleep stage transitions (n=475). Analyses of variance were performed. The outcome of AS (complete cycle AS QS; incomplete cycle AS wakefulness [W]) was considered. In the cool environment, AS and incomplete cycles increased whereas QS decreased. There was no difference in the optimum range of body temperatures at which QS or wakefulness occurred after an AS episode. QS and AS episodes differed according to the magnitude and time patterns of body temperatures and Vo₂. Throughout QS, a progressive decline of Vo₂ and of body temperatures was found. The fall in Vo₂ commenced during the preceding episode of AS. Our results also suggest that in neonates exposed to a cool environment, thermoregulation prevails over the need to conserve energy since QS decreases and W increases.

Sleep and Wakefulness Auditory Processing: Cortical Units vs. Hippocampal Theta Rhythm
Marisa Pedemonte, Lucía Pérez-Perera, José L. Peña and Ricardo A. Velluti

A physiological approach to the understanding of the central nervous system auditory processing during behavior requires taking into account the mechanisms of perception, attention and sleep/wakefulness generation. The correlation of the neuronal discharge with the hippocampal theta rhythm has been described for motor and sensory modalities. In this article we address the question of the relationship between unitary activity in the auditory cortex (AI) and the hippocampal theta rhythm. We observed there is a phase-locking between the cortical units and theta waves that was not present after data "shuffling." It may or may not depend on the power of theta hippocampal field potential. On changing behavioral state, a temporal relationship—phase-locking—was found during wakefulness, slow wave sleep and paradoxical sleep. Besides, this correlation may shift when neurons are acoustically stimulated and the same neuron could show different correlation for the spontaneous and evoked activities. The influence that attention processes exert on hippocampal activity may indicate a point of interaction between those processes and the changes in the pattern of discharge of auditory neurons in sleep and wakefulness. Our results are indicative of a new approach for sensory processing analysis in relation to behavioral states and particularly with sleep.

Evidence for a Circadian Distribution of Eye Movement Density During REM Sleep in Humans
Clemens Witzenhausen, Frederik W. Bes and Hartmut Schulz

The aim of the present study was to assess the circadian variation of rapid eye movement density (REMD) in night sleep and daytime naps of young males. Daytime naps were scheduled in 12 healthy young males at 2-h intervals between 0800 and 2400 h. Each subject performed nine naps which were scheduled in randomized order across nine nonconsecutive days. A double-nap strategy was applied with 30 min of sleep in Nap A and one complete REM sleep episode in Nap B. Naps A and B were separated by a 10-min break. All night sleep recordings were performed for each subject at the beginning and the end of the series of naps. REM density was calculated for REM sleep episodes in Nap B and for each REM episode of the two nights. REM density was defined as the ratio of the number of 3-sec epochs of REM sleep with at least one rapid eye movement and the total number of all 3-sec epochs with REM sleep. REM density showed a steady decrease from morning to late evening. During night sleep, REM density increased from the first to the second and last third of the night. REM density paralleled the circadian distribution of tonic REM sleep parameters, which is roughly inverse to that of body temperature. These results show that not only tonic but also phasic parameters of REM sleep display a circadian distribution.

Pain and Sleep in Medical Diseases: Interactions and Treatment Possibilities
Asbjørn Mohr Drewes and Lars Arendt-Nielsen

Epidemiological and clinical studies have given support for a strong association between pain and sleep disturbances. The present article reviews the present literature on pain and sleep in different patient groups with focus on studies based on objective sleep measurements. In most studies of pain patients, different sleep disturbances with alterations in sleep structure and discrete electroencephalography (EEG) abnormalities, such as alpha-EEG anomaly, were seen. A majority of studies have included patients with musculoskeletal disorders, but also in other pain patients, sleep fragmentation and disturbances of sleep microstructure may aggravate the pain and contribute to the daytime symptoms. Experimental studies in healthy subjects have given support to the hypothesis based on the clinical findings, and it is hypothesized that increased sleep depth may facilitate the sleep continuity in pain patients. Although changes in sleep structure are frequent in pain patients, the importance in the individual patient is yet unknown. Thus, in the clinic, sleep recordings are only recommended in selected patients with severe complaints of disturbed sleep and/or related daytime complaints. Several analgesics have the potential to alter the sleep structure and this may limit the use of these drugs in pain patients. Most studies were, however, performed in healthy individuals and the long-term effect of analgesics on sleep structure should be evaluated in patients with chronic pain. Short-term use of hypnotics may be of some value in selected patients as they can improve sleep satisfaction and increase daytime energy. Pain, however, is probably only affected to a minor degree by these drugs and additional treatment must frequently be recommended. Future studies are highly recommended in this area and should rely on controlled, objective experiments where polysomnography is performed together with signal analysis of the EEG microstructure.

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