Auditory arousal thresholds of good sleepers and poor sleepers with and without flurazepam.

Auditory arousal thresholds of good (N = 12) and poor (N = 12) sleepers (sleep onset insomniacs) were obtained during stage 2, stage 4, and REM sleep at various times of the night. Despite claims of being "light" sleepers who are easily awakened by noise, poor sleeper auditory arousal thresholds were the same as those of good sleepers. Flurazepam (30 mg) increased the auditory arousal thresholds of poor sleepers (N = 6), but the increase was statistically significant only during the period of peak effect which occurred 1--2 hr after ingestion. Consistent with poor sleeper complaints of trouble falling asleep, the return to sleep (i.e., sleep latency) was significantly longer for poor than for good sleepers following stimulus arousals during the first stage 2 and first stage 4 periods of the night. Sleep latencies for good and poor sleepers did not differ significantly following subsequent arousals. The sleep latency following the first stage 2 stimulus arousal was significantly reduced in poor sleepers during flurazepam-induced sleep.     

Behavioral and psychophysiological correlates of irregularity in chronic sleep routines.

Behavioral and psychophysiological correlates of irregularity in chronic sleep routines were studied. Two groups each of 18 healthy male university students were classified as either irregular sleepers or control subjects according to retrospective questionnaires, and sleep chart criteria. The control group was composed of persons who slept naturally from 12-8:00 a.m. for 7-8 hr. Irregular sleepers were defined as those whose retiring and awakening times varied by about 2-4 hr. Measurements were obtained from an auditory reaction time task, a mood adjective check list, of sublingual temperature and pulse rate 30 min. after awakening in the (a) morning, at (b) noon, in the (c) afternoon and (d) early evening following an electroencephalographically recorded 12-8:00 a.m. sleep night. At various points in the diurnal cycle irregular sleepers compared with the control group had significantly lower levels of pulse rate and body temperature, but significantly longer reaction times. During the four time periods negative affects (deactivation-sleep, depression, general deactivation, inert-fatigued) were significantly greater and positive mood states (cheerful, energetic, general activation--significantly less in the irregular sleepers. The irregular sleepers averaged significantly less stage 4, and REM, but more stage 2 and transitions between sleep stages. The present results indicate that relatively lowered levels of physiological arousal indexes, psychomotor performance and subjective mood are associated with irregularity in chronic sleep routines of young adult males. These psychobehavioral correlates of chronically maintained sleep pattern variations complement and extend previous findings on degradations in waking functions following acute 2-4 hr temporal shifts of habitual sleep periods. It is postulated that there were psychobehavioral deficits in the irregular sleepers attributable either to selective sleep stage (REM and/or stage 4) deprivation or to the more general consequence of disturbed sleeping patterns per se or to both of these factors.     

Effects of alpha-fluoromethylhistidine on sleep-waking parameters in rats

Effects of alpha-fluoromethylhistidine (FMH), an irreversible inhibitor of histidine decarboxylase, on the sleep-waking parameters were studied in rats for 24 hours. Intraperitoneal administration of FMH (100 mg/kg) at 11:30 hr resulted in a longer sleep latency compared with the control values. Hour-to-hour analyses revealed that wakefulness (W) time decreased (from 20:00 to 07:00 hr) and slow wave sleep (SS) time increased (from 19:00 to 06:00 hr) in the night. Paradoxical sleep (PS) time did not parallel the SS changes; it was increased significantly from 07:00 to 11:00 hr in the next morning. The influence of FMH seemed to be divided into direct, immediate action (increase of W) and late, prolonged action (decrease of W), and the results obtained support the histamine arousal hypothesis.     

Experimentally induced arousals during sleep: a cross-modality matching paradigm

Micro-arousals occur spontaneously or in response to exogenous and endogenous sensory input during sleep. The function of micro-arousals remains unclear, for example, whether it reflects a disturbance or a preparatory response to environmental changes. The goal of this study was to assess arousal responsiveness when two types of sensory stimulations were used: auditory (AD) alone and the addition of a vibrotactile (VT) sensation. Ten normal sleepers participated in three nights of polygraphic recordings. The first night was for habituation and to rule out sleep disorders, and the second to collect baseline sleep data. During the third night, AD and VT + AD stimuli, with three levels of intensities for auditory and vibratory signals, were randomly given to induce arousal responses in sleep stages 2, 3 and 4 and rapid eye movement (REM). The frequency of the arousal responses increased with stimulus intensity for all sleep stages and was lowest in stages 3 and 4. In non-REM (NREM) sleep, combined VT + AD stimulation induced more frequent and more intense arousal responses than AD alone. In REM sleep, more frequent micro-arousals rather than awakenings were triggered by combined stimulations. In stage 2, the response rate of total induced K-complexes did not differ between both types of stimulations while more K-complexes followed by arousals were evoked by the combined VT + AD stimulation than by the AD alone. The induced arousals were associated with an increase in heart rate in all sleep stages. An increase in suprahyoid muscle tone was observed in NREM sleep only, REM being not associated with a rise in muscle tone following experimental stimulation. Most leg and body movements occurred in response to induced awakenings. These results suggest that the cross-modality sensory stimuli triggered more arousal responses in comparison with single-modality stimuli. In an attempt to wake a sleeping subject, the addition of a tactile stimulation, such as shaking the shoulder, is an effective strategy that increases the arousal probability.     

The relationship between frequency of rapid eye movements in REM sleep and SWS rebound

Previous studies have shown a decrease in rapid eye movement (REM) frequency during desynchronized sleep in recovery nights following total or partial sleep deprivation. This effect has been ascribed to an increase in sleep need or sleep depth consequent to sleep length manipulations. The aims of this study were to assess REM frequency variations in the recovery night after two consecutive nights of selective slow-wave sleep (SWS) deprivation, and to evaluate the relationships between REM frequency and SWS amount and auditory arousal thresholds (AAT), as an independent index of sleep depth. Ten normal males slept for six consecutive nights in the laboratory: one adaptation, two baseline, two selective SWS deprivation and one recovery night. SWS deprivation allowed us to set the SWS amount during both deprivation nights close to zero, without any shortening of total sleep time. In the ensuing recovery night a significant SWS rebound was found, accompanied by an increase in AAT. In addition, REM frequency decreased significantly compared with baseline. This effect cannot be attributed to a variation in prior sleep duration, since there was no sleep loss during the selective SWS deprivation nights. Stepwise regression also showed that the decrease in REM frequency is not correlated with the increase in AAT, the traditional index of sleep depth, but is correlated with SWS rebound.     

Ontogenetic variations in auditory arousal threshold during sleep

Developmental variations in auditory arousal thresholds during sleep were investigated in four groups of normal male subjects - children, preadolescents, adolescents, and young adults. Arousal thresholds were determined during NREM and REM sleep for tones presented via earphone insert on a single night following two adaptation nights of undisturbed sleep. Age-related relationships were observed for both awakening frequency and stimulus intensity required to effect awakening, with awakenings occurring more frequently in response to lower stimulus intensities with increasing age. Although stimulus intensities required for awakening were high and statistically equivalent across sleep stages in nonadults, higher intensity stimuli were required in Stage 4 relative to Stage 2 and REM sleep in adults. These results confirm previous observations of marked resistance to awakening during sleep in preadolescent children and suggest that processes underlying awakening from sleep undergo systematic modification during ontogenetic development.     

Waking quantitative electroencephalogram and auditory event-related potentials following experimentally induced sleep fragmentation

STUDY OBJECTIVES: Experimental sleep fragmentation involves inducing arousals by administering intrusive auditory stimuli throughout the night. It is intended to model the frequent and periodic disruption experienced in common sleep disorders. Sleep fragmentation leads to daytime sleepiness, although evidence of performance impairment has been inconsistent. The purpose of this study was to investigate brain physiology associated with this level of sleep disruption. Specifically, quantitative analysis of electroencephalography was carried out, and auditory event-related potentials were recorded during daytime performance assessment following sleep fragmentation in good sleepers. DESIGN: Participants spent 4 consecutive 24-hour periods in the laboratory. On nights 2 and 3, sleep was fragmented using auditory stimuli that were delivered with increasing intensity until an arousal was noted. This design aimed to investigate the cumulative effects of sleep fragmentation on daytime functioning. SETTING: Data were collected in a sleep research laboratory during a 96-hour protocol. PARTICIPANTS: Eight healthy adults (mean age = 33.25) with no sleep complaints. MEASUREMENTS AND RESULTS: During the day, participants performed a 40-minute computerized test battery at 2-hour intervals (9:00 am -7:00 pm). The battery was presented in a fixed order and included measures of mood, sleepiness, reaction time, and serial addition or subtraction. Results indicated that subjective sleepiness and mood were impaired following sleep-fragmentation nights, compared to both baseline and recovery conditions. No performance deficits were apparent. The alpha:theta ratio, reflecting relative slowing of the electroencephalogram, was dramatically reduced following the second night of sleep fragmentation. Reductions in N1 amplitude of the event-related potentials indicated that attention was impaired with respect to early encoding processes following sleep fragmentation. CONCLUSIONS: Electroencephalographic and event-related potentials data illustrate impairment in information-processing capabilities associated with reduced arousal elicited by experimental sleep fragmentation. This subtle degree of sleep disruption, where total sleep time is not reduced, leads to sustained impairment in alertness and attention.     

Habituation of the infant arousal response.

STUDY OBJECTIVES: Arousal is considered to be an important protective response in a sleeping infant and its depression could leave an infant vulnerable to a life threatening stimulus. We found previously that arousal to a non-respiratory (tactile) stimulus occurs in a sequence of events that begins with spinal, followed by brainstem responses, and then a cortical electroencephalographic (EEG) arousal response. We hypothesized that repeated stimuli would depress the arousal responses by habituation and that spinal and brainstem responses would be more resistant to habituation than cortical responses. PARTICIPANTS: We studied 22 normal infants. INTERVENTIONS: The infants underwent polysomnographic monitoring during a daytime nap. Tactile stimuli was applied to the infants foot at 5-second intervals. MEASUREMENTS AND RESULTS: We found that spinal, brainstem, and cortical responses occurred on the first trial of each test. Repeated trials during non-rapid eye movement (NREM) and rapid eye movement (REM) sleep resulted in a decrease in the incidence of each individual response and eventually elimination of the arousal responses. Cortical responses were eliminated first, followed by brainstem responses and finally spinal responses. The elimination of each of the responses occurred more rapidly during REM sleep that during NREM sleep. CONCLUSIONS: Habituation of the infant arousal sequence occurs with repeated tactile stimulation. There is a serial habituation of responses from the cortical to the spinal level, which occurs more rapidly during REM sleep. Rapid habituation to innocuous stimuli is probably beneficial in avoiding detrimental sleep disruptions. However, in situations requiring the protective functions of arousal, such habituation could be detrimental to an infant.     

The Reliability of Arousal Threshold During Sleep

Thirty-five subjects from two independent studies were awakened at EEG-defined periods during the night with 1000 Hz ascending tone series. Awakenings were made five to eight times per night during stage 2, stage 4, or REM sleep over a series of nights in good and poor sleepers. Reliability was assessed within stage, within night, between stages, and between nights. Good and poor sleepers did not differ in either depth of sleep or reliability of arousal threshold and were thus pooled in the analyses. From night to night, the most consistency was seen in stage 4 (r=.74), although REM reliability (r?₁= .49) and stage 2 reliability (r?₁= .50 and r?₁= .69 in the two respective studies) estimates were also greater than zero. Early sleep onset and morning arousals were more variable. Reliability estimates on arousal thresholds taken within the same night for stage 2 were r= .64 and r?₁= .77 for the two studies and r= .96 for REM. The depth of sleep was not correlated with awake auditory threshold. It was concluded that five or six carefully placed arousals could give a good estimate of an individual's usual arousal threshold.     

Effects of age and sleeping position on arousal from sleep in preterm infants

STUDY OBJECTIVES: Preterm infants are at increased risk of sudden infant death syndrome (SIDS). We investigated whether the prone sleeping position impaired arousal from sleep in healthy preterm infants and whether this impairment was related to cardiorespiratory variables, temperature or postnatal age. DESIGN: Longitudinal SETTING/PARTICIPANTS: 14 healthy preterm infants (mean 32 +/- 0.4 weeks) were studied using daytime polysomnography on 4 occasions: 36-38 weeks postconception age, 2 to 3 weeks postterm, 2 to 3 months postterm, and 5 to 6 months postterm. Interventions: N/A. MEASUREMENTS: Multiple measurements of arousal threshold (cm H2O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep and quiet sleep when infants slept both prone and supine. RESULTS: Arousal thresholds were significantly higher in both AS and QS when infants slept prone at 36 to 38 weeks postconception age and 2 to 3 months postterm but not at 2 to 3 weeks or 5 to 6 months postterm. These increases were independent of any sleep position-related changes in either rectal or abdominal skin temperature, respiratory rate, oxygen saturation or heart rate. CONCLUSIONS: At the age when the risk of SIDS is highest, the prone position significantly impairs arousal from both active sleep and quiet sleep in healthy infants born prematurely. This impairment in arousability occurred with no clinically significant changes in cardiorespiratory parameters or body temperature. Decreased arousability from sleep in the prone position may explain its role as a risk factor for SIDS.     

Spontaneous arousability in prone and supine position in healthy infants

STUDY OBJECTIVE: Compared with control infants, those who will be future victims of sudden infant death syndrome (SIDS) show a decreased arousability during sleep, with fewer cortical arousals and more-frequent subcortical activations. These findings suggest an incomplete arousal process in victims of SIDS. Prone sleep position, a major risk factor for SIDS, has been reported to reduce arousal responses during sleep. The present study was undertaken to evaluate whether the prone sleep position impairs the arousal process in healthy infants. METHODS: Twenty-four healthy infants were studied polygraphically during 1 night; 12 infants regularly slept supine and 12 infants regularly slept prone. Infants were matched for sex, gestational age, and age at recording. Arousals were differentiated into subcortical activations or cortical arousals, according to the presence of autonomic and/or electroencephalographic changes. Frequencies of subcortical activations and cortical arousals were compared in the prone- and the supine-sleeping infants. RESULTS: Compared with supine sleepers, prone sleepers had significantly fewer cortical arousals during rapid eye movement (REM) sleep (p = .043). There were no significant differences in cortical arousals between the 2 groups during non-REM sleep. No significant differences were seen in the frequencies of subcortical activations during both REM and non-REM sleep between supine and prone sleepers. The ratio of cortical arousal to subcortical activation showed no significant differences between the prone and the supine sleepers. CONCLUSIONS: Prone sleep position decreased the frequency of cortical arousals but did not change the frequency of subcortical activations, as has been previously found in SIDS victims. These results suggest specific pathways for impairment of the arousal process in SIDS victims.     

Increased production of evoked and spontaneous K-complexes following a night of fragmented sleep

STUDY OBJECTIVES: To determine whether K-complex production is better interpreted as being an arousal response or reflective of a sleep protective micro-state. DESIGN: A 3-night study--night 1 as a baseline night, night 2 as a sleep fragmentation night, followed immediately by night 3 as a recovery night. On nights 1 and 3, approximately 400 auditory stimuli were presented during nonREM sleep in the first two sleep cycles, using stimulus parameters previously found to be optimal for K-complex production. SETTING: The sleep research laboratory at the University of Melbourne. PARTICIPANTS: Six young healthy subjects (3 female). INTERVENTIONS: One night of sleep fragmentation. Ten-second auditory tones of up to 110 dB were presented throughout the entire night at approximately 1-minute intervals. MEASUREMENTS AND RESULTS: Sleep drive was increased on the recovery night, as indicated by increased amounts of slow wave sleep, increased sleep efficiency, and a reduction in stimulus-related alpha activity. The incidence of both evoked and spontaneous K-complexes increased significantly on the recovery night. When K-complex trials were averaged, neither N550 (Fz) amplitude nor latency differed between the 2 nights. When vertex sharp waves were averaged, N350 (Cz) amplitude was increased significantly on the recovery night. CONCLUSIONS: The increase in K-complex frequency together with the decrease seen in stimulus-related alpha activity supports the view that they reflect a sleep maintenance, rather than an arousal, response.     

Corticospinal excitability and sleep: a motor threshold assessment by transcranial magnetic stimulation after awakenings from REM and NREM sleep

Transcranial magnetic stimulation (TMS) is a recently established technique in the neurosciences that allows the non-invasive assessment, among other parameters, of the excitability of motor cortex. Up to now, its application to sleep research has been very scarce and because of technical problems it provided contrasting results. In fact delivering one single suprathreshold magnetic stimulus easily awakes subjects, or lightens their sleep. For this reason, in the present study we assessed motor thresholds (MTs) upon rapid eye movement (REM) and non-rapid eye movement (NREM) sleep awakenings, both in the first and in the last part of the night. Taking into account that a full re-establishment of wake regional brain activity patterns upon awakening from sleep needs up to 20-30 min, it is possible to make inferences about the neurophysiological characteristics of the different sleep stages by analyzing the variables of interest immediately after provoked awakenings. Ten female volunteers slept in the lab for four consecutive nights. During the first night the MTs were collected, following a standardized procedure: 5 min before lights off, upon stage 2 awakening (second NREM period), upon REM sleep awakening (second REM period), upon the final morning awakening (always from stage 2). Results showed that MTs increased linearly from presleep wakefulness to REM sleep awakenings, and from the latter to stage 2 awakenings. There was also a time-of-night effect on MTs upon awakening from stage 2, indicating that MTs decreased from the first to the second part of the night. The increase in corticospinal excitability across the night, which parallels the fulfillment of sleep need, is consistent with the linear decrease of auditory arousal thresholds during the night. The maximal reduction of corticospinal excitability during early NREM sleep can be related to the hyperpolarization of thalamocortical neurons, and is in line with the decreased metabolic activity of motor cortices during this sleep stage. On the contrary, the increase of MTs upon REM sleep awakenings should reflect peripheral factors. We conclude that our findings legitimate the introduction of the TMS technique as a new proper tool in sleep research.     

Of sleep state and postnatal age on arousal responses induced by mild hypoxia in infants

STUDY OBJECTIVES: It has been suggested that mild hypoxia may not be a potent stimulus for arousal during sleep in infants because infants frequently fail to arouse from quiet sleep (QS). Our aim was to characterize arousal responses of sleeping infants in both active sleep (AS) and QS under normoxic and mildly hypoxic (15% O2) conditions over the first 6 months of life. PARTICIPANTS: Five healthy term and 6 healthy preterm infants were each studied at 2 to 5 weeks, 2 to 3 months, and 5 to 6 months postterm. All infants underwent daytime polysomnography during which nasal airflow was monitored using a purpose-built pneumotachograph. All infants were studied under both normoxic (21% O2) and hypoxic (15% O2, balance N2) conditions (presentation order randomized) in each sleep state at each study age. Tests were terminated at arousal, O2 saturation falling below 85%, or 5 minutes (failure to arouse). MEASUREMENTS: Probability of failure to arouse and mean arousal latency were compared between each experimental condition, with each infant serving as its own control. RESULTS: Infants aroused more frequently under hypoxic conditions than under normoxic conditions. Overall, arousal latencies were shorter during hypoxia compared to normoxia in both sleep states at each age. Arousal latencies were longer in QS compared to AS in both hypoxic and normoxic conditions. CONCLUSION: In sleeping infants, mild hypoxia serves as a stimulus for arousal in both AS and QS. Of particular significance is our finding that arousal from AS is readily elicited by mild hypoxia.     

The effects of total sleep deprivation, selective sleep interruption and sleep recovery on pain tolerance thresholds in healthy subjects

The aim of this study was to compare the effects of total sleep deprivation (TSD), rapid eye movement (REM) sleep and slow wave sleep (SWS) interruption and sleep recovery on mechanical and thermal pain sensitivity in healthy adults. Nine healthy male volunteers (age 26--43 years) were randomly assigned in this double blind and crossover study to undergo either REM sleep or SWS interruption. Periods of 6 consecutive laboratory nights separated by at least 2 weeks were designed as follows: N1 Adaptation night; N2 Baseline night; N3 Total sleep deprivation (40 h); N4 and N5 SWS or REM sleep interruption; N6 Recovery. Sleep was recorded and scored using standard methods. Tolerance thresholds to mechanical and thermal pain were assessed using an electronic pressure dolorimeter and a thermode operating on a Peltier principle. Relative to baseline levels, TSD decreased significantly mechanical pain thresholds (-8%). Both REM sleep and SWS interruption tended to decrease mechanical pain thresholds. Recovery sleep, after SWS interruption produced a significant increase in mechanical pain thresholds (+ 15%). Recovery sleep after REM sleep interruption did not significantly increase mechanical pain thresholds. No significant differences in thermal pain thresholds were detected between and within periods. In conclusion this experimental study in healthy adult volunteers has demonstrated an hyperalgesic effect related to 40 h TSD and an analgesic effect related to SWS recovery. The analgesic effect of SWS recovery is apparently greater than the analgesia induced by level I (World Health Organization) analgesic compounds in mechanical pain experiments in healthy volunteers.     

The sleep of co-sleeping infants when they are not co-sleeping: evidence that co-sleeping is stressful

Co-sleeping proponents consider the practice to be "natural" and a potential protection against sudden infant death syndrome (SIDS); others consider the practice of an infant sleeping in the parents' bed for prolonged periods at night to place an infant at risk for harm or death. For this study, co-sleeping was investigated from a different perspective, that is, as a significant early experience to investigate as it may have implications for the infant's development. The sleep of 101 normal, full-term infants was recorded nonintrusively in the home for 24 hr periods when they were 5 weeks and 6 months old. Infants were assigned to three groups: short-term co-sleepers, long-term co-sleepers, and non-co-sleepers. Their sleep states and wakefulness were compared at the two ages and over age. At 5 weeks and 6 months, the long-term co-sleeping infants differed significantly from the non-co-sleepers on a number of measures: At 5 weeks, they showed more quiet sleep and longer bouts of quiet sleep; and at 6 months, they also showed less active sleep, fewer arousals in active sleep, and less wakefulness. Each of these differences indicates a markedly lower arousal level in the long-term co-sleeping infants. This sleep pattern has been repeatedly found to be an indicator of stress. We infer that a major source of stress for these infants is the experience of sleep disturbance documented for infants when they were co-sleeping. Based on extensive evidence for long-term effects of early stress, we conclude that co-sleeping should have significant implications for infants' neurobehavioral development.     

Influence of ambient temperature on sleep characteristics and autonomic nervous control in healthy infants

OBJECTIVE: To evaluate the influence of ambient temperature on infant's sleep and cardiorespiratory parameters during sleep. PATIENTS AND METHOD: 20 healthy infants with a median age of 11.5 weeks (range 7 to 18 weeks) were recorded polygraphically for one night. They were exposed to 3 different ambient temperatures (20 degrees C-25 degrees C-30 degrees C). Ambient and core temperatures were measured throughout the procedure. RESULTS: Influence of ambient temperature was seen in: RESPIRATORY PARAMETERS: The frequency of central apneas increased significantly with increasing temperatures in REM sleep, but not in NREM sleep. HEART RATE (HR) PARAMETERS AND HR SPECTRAL ANALYSIS: Elevation of temperature was characterized by significantly higher basal HR, shorter RR intervals, and lower parasympathetic activity in REM and NREM sleep. SATURATION IN OXYGEN: During total sleep time, rise in temperature induced a decrease in basal oxygen saturation. During REM sleep, a greater frequency of oxygen saturation drops was associated with central apneas. CORE TEMPERATURE: With increasing ambient temperature, the rise of rectal temperature was mild. Despite this lack of significant increase, similar results were found when sleep and cardiorespiratory parameters were evaluated according to rectal temperatures. CONCLUSION: Changes in ambient temperatures associated with mild increases in body temperature significantly modified cardiorespiratory parameters and autonomic controls in healthy infants. The changes associated with increases in temperature were mainly seen during REM sleep.     

Effects of sleep fragmentation on the arousability to resistive loading in NREM and REM sleep in normal men

STUDY OBJECTIVE: In healthy subjects, arousability to inspiratory resistive loading is greater during rapid eye movement (REM) sleep compared with non-REM (NREM) sleep but is poorest in REM sleep in patients with sleep apnea. We therefore examined the hypothesis that sleep fragmentation impairs arousability, especially from REM sleep. DESIGN: Two blocks of 3 polysomnographies (separated by at least 1 week) were performed randomly. An inspiratory-loaded night followed either 2 undisturbed control nights (LN(C)) or 2 acoustically fragmented nights (LN(F)) SETTING: Sleep laboratory. PARTICIPANTS: Sixteen healthy men aged 20 to 29 years. INTERVENTIONS: In both loaded nights, an inspiratory resistive load was added via a valved facemask every 2 minutes during sleep and turned off either when arousal occurred or after 2 minutes. MEASUREMENTS AND RESULTS: During LN(F), arousability remained significantly greater in REM sleep (71% aroused within 2 minutes) compared with stage 2 (29%) or stage 3/4 (16%) sleep. After sleep fragmentation, arousability was decreased in stage 2 sleep (LN(F): 29%; LN(C): 38%; p < .05) and low in early REM sleep, increasing across the night (p < .01). In stage 3/4 sleep, neither an attenuation nor a change across the night was seen after sleep fragmentation. CONCLUSIONS: Mild sleep fragmentation is already sufficient to attenuate arousability in stage 2 sleep and to decrease arousability in early, compared with late, REM sleep. This means that sleep fragmentation affects the arousal response to increasing resistance and that the effects are different in stage 2 and REM sleep. The biologic reason for this increase in the arousal response in REM sleep across the night is not clear.     

Spontaneous Skin Potential Responses in Sleeping Infants Between 24 and 41 Weeks of Conceptional Age

The goal of this study was twofold: at which conceptional age do the spontaneous skin potential responses (SPRs) appear in premature infants; are they related to the sleep cycle as they are in human adults. Twenty nine sleeping infants, conceptional age (CA) 24 to 41 weeks, were investigated with polygraphic recordings. SPRs first appeared at 28 weeks. Their number increased rapidly after 30 weeks CA. They appeared mostly simultaneously with slow wave EEG activity which in premature infants is the EEG pattern of active sleep. Unlike the spontaneous SPRs which in adults occur mainly in NREM sleep, they are in premature and full term newborns well correlated with active (or REM) sleep. The relationships between spontaneous SPRs and autonomic or phasic events of sleep are also studied.