The impact of chronic primary insomnia on the heart rate – EEG variability link

ObjectiveTo determine if chronic insomnia alters the relationship between heart rate variability and delta sleep determined at the EEG.MethodsAfter one night of accommodation, polysomnography was performed in 14 male patients with chronic primary insomnia matched with 14 healthy men. ECG and EEG recordings allowed the determination of High Frequency (HF) power of RR-interval and delta sleep EEG power across the first three Non Rapid Eye Movement (NREM)–REM cycles. Interaction between normalized HF RR-interval variability and normalized delta sleep EEG power was studied by coherency analysis.ResultsPatients showed increased total number of awakenings, longer sleep latency and wake durations and shorter sleep efficiency and REM duration than controls (p < .01). Heart rate variability across first three NREM–REM cycles and sleep stages (NREM, REM and awake) were similar between both groups. In each group, normalized HF variability of RR-interval decreased from NREM to both REM and awake. Patients showed decreased linear relationship between normalized HF RR-interval variability and delta EEG power, expressed by decreased coherence, in comparison to controls (p < .05). Gain and phase shift between these signals were similar between both groups.ConclusionsInteraction between changes in cardiac autonomic activity and delta power is altered in chronic primary insomniac patients, even in the absence of modifications in heart rate variability and cardiovascular diseases.SignificanceThis altered interaction could reflect the first step to cardiovascular disorders.     

No Effects of Slow Oscillatory Transcranial Direct Current Stimulation (tDCS) on Sleep-Dependent Memory Consolidation in Healthy Elderly Subjects

BackgroundStudies in young healthy volunteers provided evidence of a beneficial impact of an anodal time-varied transcranial direct current stimulation (tDCS) during early slow wave rich sleep on declarative memory but not on procedural memory.Objective/hypothesisThe present study investigated whether sleep-dependent memory consolidation can also be affected by slow oscillating tDCS in a population of elderly subjects.Methods26 subjects (69.1 years ± 7.7 years) received bi-frontal anodal stimulation (max. current density: 0.331 mA/cm²) during early NREM sleep in a double-blind placebo-controlled randomized crossover study. Stimulation effects on offline consolidation were tested by using a declarative and a procedural memory task. Furthermore, sleep stages were scored, EEG power was analyzed and spindle densities were assessed.ResultsIndependently from stimulation condition, performance in both memory tasks significantly decreased overnight. Stimulation revealed no significant effect on sleep-dependent memory consolidation. Verum tDCS was accompanied by significantly more time awake and significantly less NREM stage 3 sleep during five 1-min stimulation free intervals.ConclusionsThe results of the present study are in line with other studies showing that offline consolidation during sleep varies with age and is less pronounced in the elderly than in young or middle-aged subjects. Contrary to an almost identical positive study in young adults, slow oscillatory tDCS applied to the elderly failed to show a beneficial effect on memory consolidation in the present study.     

Slow oscillatory transcranial direct current stimulation (so-tDCS) during slow wave sleep has no effects on declarative memory in healthy young subjects

BackgroundThe manipulation of specific brain oscillations by applying transcranial electrical stimulation techniques in order to enhance memory processes during sleep has become an intriguing field of research. A seminal study found a positive effect of slow-oscillatory transcranial direct current stimulation (so-tDCS) on sleep-dependent consolidation of declarative memories. Since then several studies have tried to replicate this result with inconsistent findings.Objective/HypothesisThis study aimed to reexamine effects of so-tDCS on declarative memory observed in young participants based on a previously described stimulation protocol used in elderly subjects.Methods23 healthy participants (mean ± SD: 23.2 ± 1.9 years; 13 women) completed a word-pair test and a sequential finger tapping test before and after sleep. Participants received anodal so-tDCS bifrontaly at a frequency of 0.75 Hz or sham stimulation during NREM sleep N2, following a double-blind, placebo controlled, counterbalanced, randomized crossover design. Data were analyzed with respect to possible effects of stimulation on memory performances, sleep staging, spindle densities and EEG power in eight frequency bands.ResultsStimulation had no significant effect on sleep dependent memory consolidation or on sleep macro- and microstructure. Independent of stimulation, procedural memory performances increased and declarative memory performances decreased overnight. This decline was less pronounced when participants had more than one learning opportunity. Fast parietal but not slow frontal spindle densities diminished from baseline to stimulation-free intervals under both stimulation conditions.ConclusionThe present study could not reproduce the results of the seminal study in young subjects, but it is consistent with results observed in elderly subjects using the same protocol. Irrespective of stimulation, re-encoding opportunities in the word-pair test had an impact on memory strength and retrieval performance.     

Waking EEG functional connectivity in middle-aged and older adults with obstructive sleep apnea

ObjectivesThe present study aimed at investigating changes in waking electroencephalography (EEG), most specifically regarding spectral power and functional connectivity, in middle-aged and older adults with obstructive sleep apnea (OSA). We also explored whether changes in spectral power or functional connectivity are associated with polysomnographic characteristics and/or neuropsychological performance.MethodsIn sum, 19 OSA subjects (apnea-hypopnea index ≥ 20, age: 63.6 ± 6.4) and 22 controls (apnea-hypopnea index ≤ 10, age: 63.6 ± 6.7) underwent a full night of in-laboratory polysomnography (PSG) followed by a waking EEG and a neuropsychological assessment. Waking EEG spectral power and imaginary coherence were compared between groups for all EEG frequency bands and scalp regions. Correlation analyses were performed between selected waking EEG variables, polysomnographic parameters and neuropsychological performance.ResultsNo group difference was observed for EEG spectral power for any frequency band. Regarding the imaginary coherence, when compared to controls, OSA subjects showed decreased EEG connectivity between frontal and temporal regions in theta and alpha bands as well as increased connectivity between frontal and parietal regions in delta and beta 1 bands. In the OSA group, these changes in connectivity correlated with lower sleep efficiency, lower total sleep time and higher apnea-hypopnea index. No relationship was found with neuropsychological performance.ConclusionsContrary to spectral power, imaginary coherence was sensitive enough to detect changes in brain function in middle-aged and older subjects with OSA when compared to controls. Whether these changes in cerebral connectivity predict cognitive decline needs to be investigated longitudinally.     

A preliminary study of slow-wave EEG activity and insulin sensitivity in adolescents

ObjectiveThe objective was to evaluate the relationship between the time course of slow wave EEG activity (SWA) during NREM sleep and insulin sensitivity in adolescents.MethodsNine normal weight and nine overweight (BMI > 85th percentile) adolescents (13–18 years of age) participated. None of the participants had a history of sleep disordered breathing, confirmed by sleep study. Participants maintained a regularized sleep wake cycle for five days followed by overnight polysomnography in the lab or at home. An oral glucose tolerance test (OGTT) was administered after a 12 h fast and within two weeks of the sleep study. Whole body insulin sensitivity (WBISI) and homeostasis model assessment (HOMA-IR) determined insulin resistance. Power spectral analysis quantified slow-wave EEG activity (.05–3.9 Hz) and exponential regression evaluated SWA across successive NREM periods.ResultsThose who were insulin resistant and had low insulin sensitivity had less Stages 2, 3 and 4 of NREM sleep, more Stage 1, but did not sleep less than those with low resistance and high sensitivity. SWA power was significantly lower in the first NREM period and the decay rate of SWA across NREM sleep was significantly slower in the low insulin sensitivity group. Similar results were obtained after removing the influence of BMI and Tanner score.ConclusionsInsulin sensitivity in adolescents is related to SWA power and its time course, not total sleep time, regardless of BMI.     

Hippocampal slow EEG frequencies during NREM sleep are involved in spatial memory consolidation in humans

The hypothesis that sleep is instrumental in the process of memory consolidation is currently largely accepted. Hippocampal formation is involved in the acquisition of declarative memories and particularly of spatial memories. Nevertheless, although largely investigated in rodents, the relations between spatial memory and hippocampal EEG activity have been scarcely studied in humans. Aimed to evaluate the effects of spatial learning on human hippocampal sleep EEG activity, we recorded hippocampal Stereo‐EEG (SEEG) in a group of refractory epilepsy patients undergoing presurgical clinical evaluation, after a training on a spatial navigation task. We observed that hippocampal high‐delta (2–4 Hz range) activity increases during the first NREM episode after learning compared to the baseline night. Moreover, the amount of hippocampal NREM high‐delta power was correlated with task performance at retest. The effect involved only the hippocampal EEG frequencies inasmuch no differences were observed at the neocortical electrodes and in the traditional polysomnographic measures. The present findings support the crucial role of hippocampal slow EEG frequencies during sleep in the memory consolidation processes. More generally, together with previous results, they suggest that slow frequency rhythms are a fundamental characteristic of human hippocampal EEG during both sleep and wakefulness, and are related to the consolidation of different types of memories. © 2014 Wiley Periodicals, Inc.     

Sleep and risk for high blood pressure and hypertension in midlife women: the SWAN (Study of Women’s Health Across the Nation) Sleep Study

ObjectiveInadequate self-reported sleep is related to high blood pressure (BP). Our study investigated cross-sectional and longitudinal relationships between poor sleep measured by in-home polysomnography (PSG) and BP.MethodsMidlife participants (132 black, 164 white, and 59 Chinese) were from the SWAN (Study of Women’s Health Across the Nation) ancillary sleep study. In-home PSG measured sleep apnea, duration, efficiency, and electroencephalogram (EEG) total delta and beta power during nonrapid eye movement (NREM) sleep. Women subsequently were followed annually for 4.5 (1–7) years for BP and hypertensive status (>140/90 mmHg or use of antihypertensive medication). Covariates were age, race, site, and educational attainment, with time-covariates of BP medications, body mass index, diabetes mellitus (DM), cigarette smoking, and menopausal status.ResultsSleep duration and efficiency were unrelated to BP cross-sectionally or longitudinally in multivariate models. Women with higher total beta power were more likely to be hypertensive at the time of the sleep study; women with lower total delta power were more likely to show increases in diastolic BP (DBP) and to be at risk for incident hypertension across follow-up.ConclusionsLow NREM delta power may be a risk factor for future hypertension. Quantitative EEG measures are worthy of future investigations of hypertension risk.     

Unaltered EEG spectral power and functional connectivity in REM microstates in frequent nightmare recallers: are nightmares really a REM parasomnia?

BackgroundFrequent nightmares show signs of hyperarousal in NREM sleep. Nevertheless, idiopathic nightmare disorder is considered a REM parasomnia, but the pathophysiology of REM sleep in relation to frequent nightmares is controversial. Cortical oscillatory activity in REM sleep is largely modulated by phasic and tonic REM periods and seems to be linked to different functions and dysfunctions of REM sleep. Here, we examined cortical activity and functional synchronization in frequent nightmare recallers and healthy controls, during phasic and tonic REM.MethodsFrequent nightmare recallers (N = 22) and healthy controls (N = 22) matched for high dream recall spent two nights in the laboratory. Phasic and tonic REM periods from the second nights' recordings were selected to examine differences in EEG spectral power and weighted phase lag index (WPLI) across groups and REM states.ResultsPhasic REM showed increased power and synchronization in delta and gamma frequency bands, whereas tonic REM featured increased power and synchronization in the alpha and beta bands. In the theta band, power was higher during tonic, and synchronization was higher during phasic REM sleep. No differences across nightmare and control participants or patterns representing interactions between the groups and REM microstates emerged.ConclusionsOur findings do not support the idea that abnormal REM sleep power and synchronization play a role in the pathophysiology of frequent nightmares. Altered REM sleep in nightmare disorder could have been confounded with comorbid pathologies and increased dream recall, or might be linked to more specific state factors (nightmare episodes).     

Periodic limb movements both in non-REM and REM sleep: Relationships between cerebral and autonomic activities

ObjectiveTo investigate the temporal relationship between cerebral and autonomic activities before and during periodic limb movements in NREM and REM sleep (PLMS).MethodsPatterns of EEG, cardiac and muscle activities associated with PLMS were drawn from polysomnographic recordings of 14 outpatients selected for the presence of PLMS both in NREM and REM sleep. PLMS were scored during all sleep stages from tibial EMG. Data from a bipolar EEG channel were analyzed by wavelet transform. Heart rate (HR) was evaluated from the electrocardiogram. EEG, HR and EMG activations were detected as transient increase of signal parameters and examined by analysis of variance and correlation analysis independently in NREM and REM sleep. Homologous parameters in REM and NREM sleep were compared by paired t-test.ResultsThe autonomic component, expressed by HR increase, took place before the motor phenomenon both in REM and NREM sleep, but it was significantly earlier during NREM. In NREM sleep, PLM onset was heralded by a significant activation of delta-EEG, followed by a progressive increase of all the other bands. No significant activations of delta EEG were found in REM sleep. HR and EEG activations positively correlated with high frequency EEG activations and negatively (in NREM) with slow frequency ones.ConclusionsOur findings suggested a heralding role for delta band only in NREM sleep and for HR during both NREM and REM sleep. Differences in EEG and HR activation between REM and NREM sleep and correlative data suggested a different modulation of the global arousal response.SignificanceIn this study, time–frequency analysis and advanced statistical methods enabled an accurate comparison between brain and autonomic changes associated to PLM in NREM and REM sleep providing indications about interaction between autonomic and slow and fast EEG components of arousal response.     

Impaired sleep-related consolidation of declarative memories in idiopathic focal epilepsies of childhood

ObjectiveDeclarative memory is consolidated during sleep in healthy children. We tested the hypothesis that consolidation processes are impaired in idiopathic focal epilepsies (IFE) of childhood in association with frequent interictal epileptiform discharges (IEDs) during sleep.MethodsA verbal (word-pair association) and a nonverbal (2D object location) declarative memory task were administrated to 15 children with IFEs and 8 control children 6–12 years of age. Patients had either centrotemporal (11 patients) or occipital (4 patients) IEDs. All but 3 patients had a history of unprovoked seizures, and 6 of them were treated with valproate (VPA). The learning procedure (location of object pairs presented on a grid; association of word pairs) was executed in the evening. Retrieval was tested immediately after learning and on the next morning after a night of sleep. Participants were tested twice, once in natural home conditions and one month later in the unfamiliar conditions of the sleep unit under EEG monitoring.ResultsOvernight recall performance was lower in children with IFE than in control children on both tasks (ps < 0.05). Performance in home conditions was similar to that in hospital conditions. Higher spike–wave index (SWI) during nonrapid eye movement (NREM) sleep was associated with poorer performance in the nonverbal task (p < 0.05). Valproate treatment was not associated with overnight recall performance for both tasks (ps > 0.05).ConclusionMemory consolidation is impaired in IFE of childhood. The association between higher SWI during NREM sleep and poorer nonverbal declarative memory consolidation supports the hypothesis that interictal epileptic activity could disrupt sleep memory consolidation.     

Association between waking electroencephalography and cognitive event-related potentials in patients with obstructive sleep apnea

ObjectiveSleepiness, cognitive deficits, abnormal event-related potentials (ERP), and slowing of the waking electroencephalography (EEG) activity have been reported in patients with obstructive sleep apnea (OSA). Our study aimed at evaluating if an association exists between the severity of ERP abnormalities and EEG slowing to better understand cerebral dysfunctions in OSA.MethodsTwelve OSA patients and 12 age-matched controls underwent an overnight polysomnographic recording, an EEG recording of 10 min of wakefulness, and an auditory ERP protocol known to specifically recruit attention. P300 and P3a ERP components were measured as well as the spectral power in each frequency band of the waking EEG. Pearson product moment correlations were used to measure associations between ERP characteristics and EEG spectral power in OSA patients and control subjects.ResultsA positive correlation between the late P300 amplitude and θ power in the occipital region was observed in OSA subjects (P < .01). A positive correlation was also found between P3a amplitude and β1 power in central region in OSA subjects (P < .01). No correlation was observed for control subjects.ConclusionsERP abnormalities observed in an attention task are associated with a slowing of the waking EEG recorded at rest in OSA.     

The relationship of alpha and delta EEG frequencies to pain and mood in 'fibrositis' patients treated with chlorpromazine and L-tryptophan

Aspects of sleep stage evaluation and analysis of alpha and delta EEG frequencies in sleep were shown to be related to musculo-skeletal pain and mood disturbance in patients with 'fibrositis syndrome'. Patients were treated at bedtime for 3 weeks with either chlorpromazine, 100 mg (8 patients), or L-tryptophan, 5 g (7 patients). Chlorpromazine, but not L-tryptophan, was associated with increased slow wave sleep and amelioration of pain and mood symptoms. Mean percent time/min or mean percent power/min of alpha frequency during NREM and REM sleep corrlated with overnight increase in pain measures, hostility, and decrease in energy. On the other hand, mean percent time/min of delta in NREM sleep was related to overnight decrease in pain and mean percent delta power/min was associated with decreased anxiety and hostility, and increased energy.     

Longitudinal assessment of NREM sleep EEG in typically developing and medication-free ADHD adolescents: first year results

ObjectiveClinical observation and structural MRI studies suggest that delayed brain maturation is a major cause of attention deficit hyperactivity disorder (ADHD). Sleep electroencephalogram (EEG) which exhibits major changes across adolescence provides an opportunity to investigate brain electrophysiology evidence for maturational delay. We present data from an ongoing longitudinal study of sleep EEG in medication-free ADHD and typically developing adolescents to investigate brain electrophysiological evidence for this maturational delay.MethodsNine adolescents diagnosed with ADHD (combined presentation, DSM-V criteria, mean age 12.39 ± 0.61 years, 2 females), and nine typically developing controls (12.08 ± 0.35 years, 4 females) were recruited. Subjects underwent an adaptation night and all night polysomnography twice yearly at the Laboratory.ResultsBasic sleep structure did not differ between the ADHD and control groups. In addition, we found no group differences on delta power (p = 0.77), but found a possible trend toward higher theta power (p = 0.057) for the ADHD group. The decline of standardized delta power across the 4 non-rapid eye movement (NREM) periods differed by group (p < 0.05) with the percent delta power in the first NREM period being lower in the ADHD group.ConclusionsOur data support the preponderant evidence that basic sleep structure is unaltered with ADHD. Our data do suggest altered sleep homeostatic recuperative processes in ADHD. The theta findings from the first two recordings are suggestive of a maturational delay associated with ADHD, but follow-up data-points are needed.     

Quantitative analysis of sleep EEG microstructure in the time–frequency domain

A number of phasic events influence sleep quality and sleep macrostructure. The detection of arousals and the analysis of cyclic alternating patterns (CAP) support the evaluation of sleep fragmentation and instability.Sixteen polygraphic overnight recordings were visually inspected for conventional Rechtscaffen and Kales scoring, while arousals were detected following the criteria of the American Sleep Disorders Association (ASDA). Three electroencephalograph (EEG) segments were associated to each event, corresponding to background activity, pre-arousal period and arousal. The study was supplemented by the analysis of time–frequency distribution of EEG within each subtype of phase A in the CAP.The arousals were characterized by the increase of alpha and beta power with regard to background. Within NREM sleep most of the arousals were preceded by a transient increase of delta power.The time–frequency evolution of the phase A of the CAP sequence showed a strong prevalence of delta activity during the whole A1, but high amplitude delta waves were found also in the first 2/3 s of A2 and A3, followed by desynchronization.Our results underline the strict relationship between the ASDA arousals, and the subtype A2 and A3 within the CAP: in both the association between a short sequence of transient slow waves and the successive increase of frequency and decrease of amplitude characterizes the arousal response.     

Estimation of parasympathetic nerve function during sleep in patients with obstructive sleep apnea by instantaneous time–frequency analysis

Background and objectivesThe pathophysiologic aspects of parasympathetic nerve (PN) function during sleep in patients with obstructive sleep apnea (OSA) studied by classical power spectrum analysis on heart rate variability (HRV) are highly controversial. The controversy is attributed to methodologic concerns, such as poor time resolution involved in power spectrum analysis. We aimed to establish the appropriate method for the investigation of PN function in OSA patients with apneas and hypopneas using instantaneous time–frequency analysis with complex demodulation (CD) and sufficient time resolution.MethodsA total of 30 patients with PSG-confirmed mild to severe OSA were recruited for the analysis of frequency spectra contained in R-R intervals (RRI) of overnight electrocardiograph (ECG) tracings. High-frequency (HF) domains ranging between 0.15 and 0.40 Hz were selected for analysis. Among these domains, the HF domain with the maximum instantaneous amplitude was defined as the main HF peak and was used as the surrogate marker of PN discharge. Based on density spectrum array (DSA) map for main HF peak constructed with a time scale of 1 s and a frequency resolution of 0.002 Hz (HF-DSA map), the shift in central frequency (CF) of main HF peak over time was continuously monitored. When the main HF peak with the same CF lasted for more than 20 s or 5 min on HF-DSA map, the PN function was considered to be stable or very stable. The measurements were then repeated after continuous positive airway pressure (CPAP) treatment.ResultsThe extent of PN-evoked modulation of RRI was enhanced in nonrapid eye movement (NREM) sleep, though the stability was reduced in both NREM and rapid eye movement (REM) sleep. These peculiar behaviors of PN function were reversed by CPAP treatment.ConclusionWe found that instantaneous time–frequency analysis allowed estimation of transitional changes in PN function during sleep in OSA patients.     

Optimizing computation of overnight decline in delta power: Evidence for slower rate of decline in delta power in insomnia patients

ObjectiveTo determine the best of commonly used methods for computing the rate of decline in non-rapid eye movement (NREM) sleep EEG delta power overnight (Delta Decline) in terms of vulnerability to missing data and to evaluate whether this rate is slower in insomnia patients than healthy controls (HC).MethodsFifty-one insomnia patients and 53 HC underwent 6 nights of polysomnography. Four methods for estimating Delta Decline were compared (exponential and linear best-fit functions using NREM (1) episode mean, (2) peak, and (3) total delta power and (4) delta power for all available NREM epochs). The best method was applied to compare groups on linear and exponential rates of Delta Decline.ResultsBest-fit models using all available NREM epochs were significantly less vulnerable to deviation due to missing data than other methods. Insomnia patients displayed significantly slower linear and exponential Delta Decline than HC.ConclusionsComputing Delta Decline using all available NREM epochs was the best of the methods studied for minimizing the effects of missing data. Insomnia patients display slower Delta Decline, which is not explained by differences in total sleep time or wake after sleep onset.SignificanceThis study supports using all available NREM epochs in Delta Decline computation and suggests a slower rate in insomnia.     

Evaluation of an automated pipeline for large-scale EEG spectral analysis: the National Sleep Research Resource

Study objectivesWe present an automated sleep electroencephalogram (EEG) spectral analysis pipeline that includes an automated artifact detection step, and we test the hypothesis that spectral power density estimates computed with this pipeline are comparable to those computed with a commercial method preceded by visual artifact detection by a sleep expert (standard approach).MethodsEEG data were analyzed from the C3-A2 lead in a sample of polysomnograms from 161 older women participants in a community-based cohort study. We calculated the sensitivity, specificity, accuracy, and Cohen's kappa measures from epoch-by-epoch comparisons of automated to visual-based artifact detection results; then we computed the average EEG spectral power densities in six commonly used EEG frequency bands and compared results from the two methods using correlation analysis and Bland–Altman plots.ResultsAssessment of automated artifact detection showed high specificity [96.8%–99.4% in non-rapid eye movement (NREM), 96.9%–99.1% in rapid eye movement (REM) sleep] but low sensitivity (26.7%–38.1% in NREM, 9.1–27.4% in REM sleep). However, large artifacts (total power > 99th percentile) were removed with sensitivity up to 87.7% in NREM and 90.9% in REM, with specificities of 96.9% and 96.6%, respectively. Mean power densities computed with the two approaches for all EEG frequency bands showed very high correlation (≥0.99). The automated pipeline allowed for a 100-fold reduction in analysis time with regard to the standard approach.ConclusionDespite low sensitivity for artifact rejection, the automated pipeline generated results comparable to those obtained with a standard method that included manual artifact detection. Automated pipelines can enable practical analyses of recordings from thousands of individuals, allowing for use in genetics and epidemiological research requiring large samples.     

Reduced fronto-cortical brain connectivity during NREM sleep in Asperger syndrome: An EEG spectral and phase coherence study

Objective

To investigate whether sleep macrostructure and EEG power spectral density and coherence during NREM sleep are different in Asperger syndrome (AS) compared to typically developing children and adolescents.

Methods

Standard all night EEG sleep parameters were obtained from 18 un-medicated subjects with AS and 14 controls (age range: 7.5–21.5 years) after one adaptation night. Spectral, and phase coherence measures were computed for multiple frequency bands during NREM sleep.

Results

Sleep latency and wake after sleep onset were increased in AS. Absolute power spectrum density (PSD) was significantly reduced in AS in the alpha, sigma, beta and gamma bands and in all 10 EEG derivations. Relative PSD showed a significant increase in delta and a decrease in the sigma band for frontal, and in beta for centro-temporal derivations. Intrahemispheric coherence measures were markedly lower in AS in the frontal areas, and the right hemisphere over all EEG channels. The most prominent reduction in intrahemispheric coherence was observed over the fronto-central areas in delta, theta, alpha and sigma EEG frequency bands.

Conclusion

EEG power spectra and coherence during NREM sleep, in particular in fronto-cortical derivations are different in AS compared to typically developing children and adolescents.

Significance

Quantitative analysis of the EEG during NREM sleep supports the hypothesis of frontal dysfunction in AS.     

Baseline and post-deprivation recovery sleep in SCN-lesioned rats

In humans, advancing age alters sleep patterns, reducing high voltage NREM sleep, sleep bout length, and delta power during NREM sleep. Although the mechanism by which these alterations occur is unknown, age-related changes in normal circadian processes may play a role. Increased age produces histological and functional changes in the suprachiasmatic nucleus (SCN), and alters the amplitude and phase of circadian rhythms. To examine the relationship between SCN function and age-related changes in sleep, we produced radiofrequency (RF) lesions of the SCN in rats of different ages and examined sleep behavior before and after sleep deprivation. Three-, 12- and 18-month-old rats received RF or sham lesions of the SCN. After verifying loss of circadian rhythm, 24-h EEG/EMG/temperature recordings were made in dim light before and after 24 h of sleep deprivation using the disk-over-water method. Age-related changes in NREM sleep, sleep bout length, and delta EEG power persisted despite SCN lesions. SCN lesions in all age groups increased baseline NREM sleep by 4% and NREM delta power by 15%, and decreased REM sleep by 10%. Although SCN lesions initially produced more REM and NREM sleep during recovery, 24-h values did not differ. Deteriorating SCN function is unlikely to cause the characteristic changes in sleep that occur with age. Our data also imply that an intact SCN slightly inhibits NREM sleep in the rat. Changes in NREM sleep and delta EEG power during recovery in lesioned rats suggest that the SCN may influence homeostatic regulation.     

Sigma (12-15 Hz) and delta (0.3-3 Hz) EEG oscillate reciprocally within NREM sleep

Sleep EEG in the sigma and delta frequency bands was subjected to spectral analysis in 8 normal young adults. In each subject, power density of sigma and delta oscillated reciprocally during NREM sleep, confirming an observation made initially with period/amplitude analysis. In REM sleep, power density for both frequency bands was at its lowest levels. Correlation coefficients between power density of delta vs. 1/sigma for all artifact-free 20-s epochs of NREM sleep/night were highly significant for each subject. These results show that cyclic oscillation of EEG within sleep is not limited to delta frequencies. The reciprocal relation of sigma to delta holds implications for the EEG mechanisms of NREM sleep. This dynamic pattern may also prove useful for sleep stage scoring and for a finer empirical analysis of sleep in psychiatric and neurological disorders.