Section of Psychopharmacology and Sleep Research
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University of Zürich - Institute of Pharmacology and Toxicology Section of Psychopharmacology and Sleep Research |
BACKGROUND: It was recently reported that epochs of non-REM sleep (NREMS) with low muscle tone represent a partial correlate of REM sleep (REMS). To further investigate this phenomenon, episodes of restricted night-time sleep (23:00 - 03.00 h) and subsequent morning sleep (10:00-13:00 h) were analysed. RESULTS: Epochs of NREMS with low muscle tone (NLMT) were identified. Their frequency was higher in morning sleep than in night sleep. At night, the latency to the first occurrence of NLMT showed a bimodal distribution with modes at sleep onset and close to REMS onset. In morning sleep, the distribution was unimodal with the mode at sleep onset. An episode of NLMT at sleep onset occurred in 35.5% of the night sleep episodes and in 60.9% of the morning sleep episodes without sleep onset REMS (SOREMS). Also SOREMS occurred predominantly in morning sleep. REMS episodes were longer and NREMS episodes shorter in morning sleep than in night sleep, whereas cycle duration did not differ. Simulating the time course of slow-wave activity revealed a close correspondence between empirical and computed values for night sleep, and some discrepancies for morning sleep. CONCLUSIONS: The results provide further evidence that NREMS with low muscle tone is a marker of REMS regulation. NLMT at sleep onset may represent an early manifestation of REMS.
BMC Neursci. 2006 Jan 9;7(1):2
Sleep has been shown to play a facilitating role in memory consolidation, whereas sleep deprivation leads to performance impairment both in humans and rodents. The effects of 4-h sleep deprivation on recognition memory were investigated in the Djungarian hamster (Phodopus sungorus). Because sleep during the first hours after daily torpor has many similarities to recovery from sleep deprivation, the effects of spontaneous torpor on object recognition were also assessed. A 4-h sleep deprivation, starting immediately after an object learning task, diminished the ability of the hamsters to: (1) discriminate between an already encountered object (target) and a novel object presented in a novel context, (2) retrieve a target within a complex spatial scene, and (3) detect a spatial rearrangement of familiar objects in a familiar context. Plasma stress hormone levels were similar in sleep-deprived and control hamsters. The occurrence of a daily torpor episode during retention was associated with impaired old-new object discrimination performance in the more effortful complex spatial scene task only, and in a two-object choice situation in a novel context no torpor-induced deficit was found. Our results show that post learning sleep deprivation and daily torpor induce a deficit in familiar object retrieval performance in a complex spatial scene, while sparing familiarity-based recognition and novelty processing. Sleep deprivation during the first 4 h of memory consolidation hampered also recency memory for discrete objects. Stress was not a factor contributing to the sleep deprivation-induced impairment.
Physiol Behav., 2006 Jan 30;87(1)
Despite the widespread use of inbred mice in research, little is known about aging of the circadian system in female mice, although interactions between female gonadal hormones and circadian rhythms have been established. We investigated the influence of the estrus cycle on circadian aspects of running-wheel activity and changes in the course of aging in female C57BL/6 and C3H/He mice recorded continuously between the ages of 3 and 19 months. In the young, cycling mice the second part of the proestrus night was often, but not consistently, characterized by increased motor activity compared to the remaining estrus cycle nights. After estrus cycling had ceased in the course of ageing, the estrus-dependent day-to-day variability in activity was reduced. The amplitude of the daily rest-activity rhythm decreased progressively after the age of 8 months in C3H/He and 10 months in C57BL/6 mice. The capacity for resynchronisation of activity onset to the LD-cycle was compared in young and old mice after an 8-h phase advance of the LD-cycle. Resynchronisation was significantly slower in old C3H/He mice and unaffected by age in C57BL/6 mice. The circadian period in constant darkness did not change with age in either strain. However, the period was shorter in 17-month old C57BL/6 mice compared to an additional group, which was recorded at the same age, after at least 1-month adaptation to the recording conditions. The results show that the reproductive state as well as ageing influence motor activity patterns of female mice in a strain- and cohort-dependent manner.
Behav Brain Res., 2006 Feb 15;167(1):165-74.
Abstract follows.
Sleep., Vol 29. 1, 2006.
Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. Previous neuropsychological studies indicate that sleep deprivation causes impairments in prefrontal cortical function. Random number generation (RNG) is thought to provide a sensitive index of executive functions that rely on the prefrontal cortex. The present study tested the hypothesis that sleep deprivation would impair RNG and that caffeine would mitigate this impairment. Healthy young men (n ¼ 21) participated in two 40-h sleep deprivations 1 week apart. During each sleep deprivation period subjects received either caffeine or placebo according to a randomized, double-blind cross-over design, and they completed an oral RNG task at 3-h intervals. Comparison of test sessions at analogous times of day revealed that sleep deprivation was associated with significant drops in the number of responses, a threefold increase in the percentage of rule violations, 59% greater response redundancy and a 20% increase in stereotypy of adjacent response pairs. Sleep deprivation did not consistently alter counting tendency. Caffeine ameliorated the decrease in the number of responses but did not mitigate other deficits in RNG that arose during sleep deprivation. These findings are consistent with prior reports of diminished vigilance and increased perseveration during extended wakefulness. They support the conclusion that caffeine preserves simple aspects of cognitive performance during sleep deprivation, whereas caffeine may not prevent detrimental effects of sleep deprivation on some complex cognitive functions.
J. Sleep Res. (2006) 15, 31-40
We aimed to examine whether commonly observed individual differences in sleep architecture and the sleep electroencephalogram reflect individual traits, which are amenable to a genetic investigation of human sleep. We studied intraindividual stability and inter-individual variation in sleep and sleep electroencephalogram spectra across four baseline recordings of eight healthy young men. A similarity concept based on Euclidean distances between vectors was applied. Visually scored sleep variables served as feature vector components, along with electroencephalogram power spectra in non-rapid-eye-movement and rapid-eye-movement sleep. The distributions of similarity coefficients of feature vectors revealed a clear distinction between high within-subject similarity (i.e. stability), and low between-subject similarity (i.e. variation). Moreover, a cluster analysis based on electroencephalogram spectra in both non-rapid-eye-movement and rapid-eye-movement sleep segregated all four baseline nights of each individual into a distinct cluster. To investigate whether high and low sleep pressure affects the similarity coefficients, normalized non-rapid-eye-movement sleep electroencephalogram spectra of the first and second half of the recordings were compared. Because the electroencephalogram changes systematically in the course of the night, withinsubject variation no longer differed from between-subject variation. In conclusion, our data provide evidence for traitlike characteristics in the sleep electroencephalogram. Further studies may help to identify distinct phenotypes to search for genes underlying functional aspects of undisturbed human sleep.
Neuroscience 138 (2006) 321-356
The development of the 24-h rest-activity pattern was investigated in human infants under naturalistic conditions as assessed by continuous actigraphy. Seven infants and their mothers were recorded for 4 (n=1), 6 (n = 5) and 12 months (n = 1) after birth. Periodogram analysis of rest-activity data was performed over consecutive 10-day intervals. A weak 24-h rest-activity pattern was already present in some infants during the newborn period. The magnitude of the 24-h component in individual periodograms increased across the first months following a saturating function. The time constants of fitted saturating exponential functions – reflecting the rate of development of the 24-h pattern – ranged from 49 to 110 days (n = 6) indicating a large interindividual variability. Furthermore, intraindividual variation was observed; the magnitude of the 24-h rest-activity component showed fluctuations around the trend. Miniaturized actigraphs are ideal tools for long-term longitudinal monitoring of rest-activity behavior in infants.
Infant Behavior & Development (2006) 29, 143-152
Background: The prevalence and characteristics of sleep-wake disturbances in sporadic Creutzfeldt-Jakob disease (sCJD) are poorly understood. Methods: Seven consecutive patients with definite sCJD underwent a systematic assessment of sleep-wake disturbances, including clinical history, video-polysomnography, and actigraphy. Extent and distribution of neurodegeneration was estimated by brain autopsy in six patients. Western blot analyses enabling classification and quantification of the protease-resistant isoform of the prion protein, PrPSc, in thalamus and occipital cortex was available in four patients. Results: Sleep-wake symptoms were observed in all patients, and were prominent in four of them. All patients had severe sleep EEG abnormalities with loss of sleep spindles, very low sleep efficiency, and virtual absence of REM sleep. The correlation between different methods to assess sleep-wake functions (history, polysomnography, actigraphy, videography) was generally poor. Brain autopsy revealed prominent changes in cortical areas, but only mild changes in the thalamus. No mutation of the PRNP gene was found. Conclusions: This study demonstrates in sporadic Creutzfeldt-Jakob disease, first, the existence of sleep-wake disturbances similar to those reported in fatal familial insomnia in the absence of prominent and isolated thalamic neuronal loss, and second, the need of a multimodal approach for the unambiguous assessment of sleep-wake functions in these patients.
Neurology (2006), 1418-1424
Background: Large individual differences characterize the changes induced by sleep deprivation on neurobehavioral functions and rhythmic brain activity. To investigate adenosinergic mechanisms in these differences, we studied the effects of prolonged waking and the adenosine receptor antagonist caffeine on sustained vigilant attention and regional electroencephalogram (EEG) power in the ranges of theta
activity (6.25– 8.25 Hz) in waking and the slow oscillation (<1 Hz) in sleep. Activity in these frequencies is functionally related to sleep deprivation. In 12 subjectively caffeine-sensitive and 10 -insensitive young men, psychomotor vigilance task (PVT) performance andEEG were assessed at 3 h intervals before, during, and after one night without sleep. After 11 and 23 h waking, subjects received 200mgcaffeine and placebo in double-blind, cross-over manner. In the placebo condition, sleep deprivation impaired PVT speed more in caffeinesensitive than in caffeine-insensitive men. This difference was counteracted by caffeine. Theta power in waking increased more in a frontalEEGderivation than in a posterior derivation. Caffeine attenuated this power gradient in caffeine sensitive subjects. Sleep loss also differently affected the power distribution<1 Hz in non-rapid eye movement sleep between caffeine sensitive and insensitive subjects. Also, this difference was mirrored by the action of caffeine. The effects of sleep deprivation and caffeine on sustained attention and regional EEG power in waking and sleep were inversely related. These findings suggest that adenosinergic mechanisms contribute to individual differences in waking-induced impairment of neurobehavioral performance and functional aspects of EEG topography associated with sleep deprivation.
The Journal of Neurosience (2006), 26(41), 10472–10479