NREM Period Research Articles

Decreased coherence in higher frequency ranges (beta and gamma) between central and frontal EEG in patients with schizophrenia: A preliminary report

Schizophrenia is associated with a dysfunction of cognitive integration that may be due to abnormalities in inhibitory neural circuitry. A previous study found a failure of gamma band (25–45 Hz) synchronization in patients with schizophrenia compared to controls. Another recent study also stressed the importance of investigating high frequencies in the scalp-recorded sleep electroencephalogram (EEG). In this study, we compared coherence between first episode drug-naïve patients with schizophrenia ( n = 8) and age- and sex-matched normal controls ( n = 8) using two 32-s epochs of C4 and F4 EEG. The coherence was obtained using 4096 data points (128 Hz signal) using cross-spectral analysis with Blackman–Tukey window in beta (15.25–24.75 Hz) and gamma (25–44.75 Hz) frequency bands. We used wake, non-rapid eye movement (NREM) and rapid eye movement (REM) sleep periods for the analyses. Our results show a significant decrease in coherence in both beta and gamma frequency bands in patients. Post-hoc ‘ t’ tests revealed a significantly lower coherence only during the wake stage in patients with schizophrenia in beta as well as gamma frequency bands. These results further support the importance of the analyses of high-frequency bands in the EEG and support previous findings of abnormal neural synchrony in patients with schizophrenia. These results have been discussed further in relation to wake and sleep stages.

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.

Electroencephalographic Activities During Wakefulness and Sleep in the Frontal Cortex of Healthy Older People: Links with “Thinking”

Separate studies have shown for the frontal cortex that: i) sleep electroencephalogram (EEG) activity less than 1 Hz may be linked to waking recovery, and ii) waking frontal theta activity may reflect "cortical workload." We explored the potential linkage between (i) and (ii) in relation to specific waking theta frequencies and 0.5-Hz to 1.0-Hz activity in sleep. A correlational study Laboratory-based waking EEGs under different (eyes-closed) contrived "thinking" conditions (mostly localized to the left frontal area), and night sleep EEGs at home. Twelve right-handed, healthy, good-sleeping, older adults (mean age, 67.3 years) EEGs comprised 4 bipolar derivations (Fp1-F3; Fp2-F4; O1-P3; O2-P4). Power in the 7-8-Hz bin was the only waking frequency significantly (positively) correlated with power in the 0.5- to 1.0-Hz bin during the first NREM period and only for the left frontal EEG. Interestingly, 7- to 8-Hz power immediately after lights out at bedtime, and before the appearance of EEG sleepiness, showed an even higher positive correlation with 0.5- to 1.0-Hz power during sleep. This wake-sleep EEG link was confirmed in another sample of 8 similar participants. Waking frontal 7- to 8-Hz EEG may not be typical theta, but "kappa" activity, believed to be associated with thinking Within limits of the EEG, and for the left frontal area, waking thinking may be reflected by putative cortical reorganization during the first NREM period.

Sleep microstructure around sleep onset differentiates major depressive insomnia from primary insomnia.

In the present study we investigate whether alterations of sleep propensity or of wake propensity are implicated in sleep initiation disturbances encountered in major depressive insomnia and in primary insomnia. For this purpose, the time course of electroencephalogram (EEG) power density during the period preceding sleep onset and during the first non-rapid eye movement (REM) period was examined in three age and gender matched groups of 10 women and 11 men (healthy controls, primary insomniacs and depressive insomniacs). In contrast to healthy controls and depressive insomniacs, patients with primary insomnia did not experience a gradual decrease of their alpha and beta1 power during the sleep onset period and had a lower delta activity in the 5 min preceding sleep onset. Compared with the two other groups, depressive patients exhibit less dynamic changes in slow wave activity during the first non-REM period. The present results suggest that hyperarousal (high 'Process W') may mainly be implicated in the sleep initiation difficulties of primary insomniacs whereas the homeostatic sleep regulation process seems to be partially maintained. In our major depressed patients, the sleep initiation disturbances appeared to relate to a lower sleep pressure (low 'Process S') rather than to hyperarousal. This study supports the idea that different mechanisms are implicated in sleep disturbances experienced by primary insomniacs and major depressive insomniacs.

Selective alterations of the first NREM sleep cycle in humans by a dopamine D1 receptor antagonist (NNC-687)

This paper details the first study of the effects of dopamine D1 receptor antagonism on the regulation of human sleep EEG (electroencephalogram). The investigational drug NNC-687 (NNC 01-0687/CEE 03-310) was administered to 20 healthy young men in doses of 5, 10, and 15 mg in a double blinded, placebo controlled, crossover design. In rats, dopamine D1 receptor antagonism can produce large increases in the amounts of both rapid eye-movement (REM) and non-rapid eye-movement (NREM) sleep. In this study, drug effects were most prominent in the first NREM period. D1 antagonism markedly reduced the peak-amplitude of delta EEG waves but increased their instantaneous frequency as well as enhancing the total number, incidence, and burst-duration of sleep spindles. The length of the first NREM period was increased up to 47% over baseline. Despite these large increases in NREM sleep time, the amount of delta EEG power accumulated over the first NREM period was conserved at baseline levels. We note that the sleep-EEG profile of D1 antagonism is very similar to that of GABA a (gamma-aminobutyric acid) receptor modulators and suggest that D1 antagonism may alter the properties of the neuronal networks which generate delta and spindle, and K-complex EEG waveforms through the upstream modulation of GABA a receptor activity.

Kinetics of non-rapid eye movement delta production across sleep and waking in young and elderly normal subjects: theoretical implications.

To perform a within-subject analysis of the changes in absolute and normalized rates of non-rapid eye movement (NREM) delta power production across daytime naps and baseline sleep, specifically to determine whether these rates change linearly or exponentially. Subjects were studied in a 2-day protocol after screening for sleep disorders. The first night was a baseline sleep recording that was followed by a nap the next day at one of the following times: 900, 1200, 1500, 1800 with the nap order varied between subjects. Sleep was then recorded on the postnap night with the baseline bedtime schedule. Subjects completed all 4 nap conditions. A 4-bed sleep research laboratory. Each subject slept in a separate bedroom. Not applicable. Subjects were young normal (YNs, mean age 22.4 yrs) and elderly normal (ENs, mean age 71.4 yrs) adults. Electroencephalography was recorded continuously during baseline, nap, and postnap sleep. Fast Fourier transform and period-amplitude analysis and visual scoring were performed. Delta power/min and period-amplitude integrated amplitude/min were significantly lower in EN than YN subjects. Both measures declined linearly across NREM periods and increased linearly across naps in the two age groups. The linear slopes for absolute power and integrated amplitude were significantly flatter in the elderly. However, when normalized to each individual subject's baseline rate of delta production, the slopes of the ENs closely approximated those of the YNs. The observation of linear changes in delta across NREM periods and daytime naps contradicts the exponential assumptions of the two-process model. The similarity of the normalized slopes shows that waking and sleep exert the same proportionate change in NREM delta in YNs and ENs. This raises the possibility that homeostatic drive is similar in the two groups despite different rates of absolute delta production. The data here, taken in association with other findings, lead us to hypothesize that NREM delta is specifically homeostatic for the neuronal systems that underlie consciousness.

Spectral analysis of all-night human sleep EEG in narcoleptic patients and normal subjects.

To investigate the pathophysiology of narcoleptic patients' sleep in detail, we analysed and compared the whole-night polysomnograms of narcoleptic patients and normal human subjects. Eight drug-naive narcoleptic patients and eight age-matched normal volunteers underwent polysomnography (PSG) on two consecutive nights. In addition to conventional visual scoring of the polysomnograms, rapid eye movement (REM)-density and electroencephalograph (EEG) power spectra analyses were also performed. Sleep onset REM periods and fragmented nocturnal sleep were observed as expected in our narcoleptic patients. In the narcoleptic patients, REM period duration across the night did not show the significant increasing trend that is usually observed in normal subjects. In all narcoleptic patient REM periods, eye movement densities were significantly increased. The power spectra of narcoleptic REM sleep significantly increased between 0.3 and 0.9 Hz and decreased between 1.0 and 5.4 Hz. Further analysis revealed that non-rapid eye movement (NREM) period duration and the declining trend of delta power density in the narcoleptic patients were not significantly different from the normal subjects. Compared with normal subjects, the power spectra of narcoleptic NREM sleep increased in the 1.0-1.4 Hz and 11.0-11.9 Hz frequency bands, and decreased in a 24.0-26.9 Hz frequency band. Thus, increased EEG delta and decreased beta power densities were commonly observed in both the NREM and REM sleep of the narcoleptic patients, although the decrease in beta power during REM sleep was not statistically significant. Our visual analysis revealed fragmented nocturnal sleep and increased phasic REM components in the narcoleptic patients, which suggest the disturbance of sleep maintenance mechanism(s) and excessive effects of the mechanism(s) underlying eye movement activities during REM sleep in narcolepsy. Spectral analysis revealed significant increases in delta components and decreases in beta components, which suggest decreased activity in central arousal mechanisms. These characteristics lead us to hypothesize that two countervailing mechanisms underlie narcoleptic sleep pathology.

EEG activities during elicited sleep onset REM and NREM periods reflect different mechanisms of dream generation. Electroencephalograms. Rapid eye movement.

To be the first to compare EEG power spectra during sleep onset REM periods (SOREMP) and sleep onset NREM periods (NREMP) in normal individuals and relate this to dream appearance processes underlying these different types of sleep periods. Eight healthy undergraduates spent 7 consecutive nights in the sleep lab including 4 nights for SOREMP elicitation using the Sleep Interruption Technique. This enabled us to control preceding sleep processes between SOREMP and NREMP. EEG power spectra when participants did and did not report 'dreams' were compared between both types of sleep. Sleep stages, subjective measurements including dream property scores, sleepiness, mood, and tiredness after awakenings were also examined to determine their consistency with EEG findings. Increased alpha EEG activities (11.72-13.67 Hz) observed mainly in the central area were related to the absence of SOREMP dreams and appearance of NREMP dreams. Analyses of sleep stages combining two studies (16 participants) also supported the Fast Fourier Transform findings, showing that when dreams were reported there were decreased amounts of stage 2 and increased stage REM in SOREMP and increased stage W in NREMP. SOREMP dreams were more bizarre than NREMP dreams. Participants felt more tired after SOREMP with dreams than without dreams, while the opposite was observed after NREMP episodes. EEG power spectra patterns reflected different physiological mechanisms underlying generation of SOREMP and NREMP dreams. The same relationships were also reflected by sleep stage analyses as well as subjective measurements including dream properties and tiredness obtained after awakenings. This study not only supports the hypothesized relationships between REM mechanisms and REM dreams as well as arousal processes and NREM dreams, it also provides a new perspective to dream research due to its unique techniques to awaken participants and collect REM dreams during experimentally induced SOREMP.

Prognostic value of evoked potentials and sleep recordings in the prolonged comatose state of children. Preliminary data

Objectives – Sleep recordings and evoked potentials (EPs) were used in five comatose children to evaluate their predictive value for outcome following a severe comatose state. Methods and subjects – The protocol included EEG, Brainstem Evoked Responses (BERs), Somatosensory Evoked Potentials (SEPs) and polysomnography. From 10 to 15 days post-coma (D10 to D15), EEG and clinical examinations were carried out every second day, then one day in four from 15 to 30 days post-coma (D15 to D30), and one day in seven from D30 to six months (M6). Evoked potentials and Polysomnography were recorded on D10–D15 or D30 in the second month (M2) and in M6. Of the five children, three were in anoxic coma and two in traumatic coma. All had extensive lesions and a Glasgow Coma Scale (GCS) score of less than five. The results of the EEG, polysomnographic and EP recordings were compared to the clinical outcome. Results and conclusion – In the three anoxic comas we observed BER abnormalities and the absence of SEP N20 associated with wide cortical lesions with brainstem extension. Sleep recordings showed major alterations of the wake-sleep cycle without any improvement in M6. Abnormalities included loss of the normal REM-sleep pattern associated with alteration of NREM sleep and periods of increase in motor activity without EEG arousal. This sleep pattern appeared to be associated with involvement of the brainstem. In the two traumatic comas, alterations of the early cortical SEP responses were less severe and the BERs were normal. Some sleep spindles were observed as well as the persistence of sleep cycles in the first weeks post-coma. The combined use of EEG, EPs and polysomnography improved the outcome prediction in comparison with the use of just one modality. EPs and sleep recordings were far superior to clinical evaluation and to GCS in the appreciation of the functional status of comatose children. The reappearence of sleep patterns is considered to be of favorable prognosis for outcome of the coma state, as is the presence of sleep spindles in post-trauma coma. This study showed that EPs and sleep recordings help to further distinguish between patients with good or bad outcomes.

Dynamics of electroencephalographic slow wave activity and body temperature during monophasic and biphasic human sleep

Dynamics of electroencephalographic (EEG) slow wave activity (0.5–4.5 Hz) and body temperature, as estimates, respectively, of the process S and process C, regulating sleep and waking alternate occurrence, were measured during monophasic and biphasic sleep patterns that occurred spontaneously in a 35-year-old woman who lived for 105 days in a winter-type photoperiod (10–14 h light–dark). In monophasic nights, rate of EEG synchronization showed a decreasing trend across the first three non-rapid eye movement (NREM) periods. In biphasic nights, rate of EEG synchronization increased during the third NREM period which precedes the nocturnal awakening. Temperature cycle was not different between biphasic and monophasic nights. Those results confirm that EEG dynamics reflects homeostatic sleep regulatory mechanism, and suggest that the period of prolonged wakefulness in the middle of biphasic night is pre-programmed.

Dynamics of Slow-Wave Activity During the NREM Sleep of Sleepwalkers and Control Subjects

To compare the number and distribution of awakenings from slow-wave sleep (SWS) and both the power and dynamics of EEG slow-wave activity (SWA) in sleepwalkers and controls. Somnambulism is considered to be a disorder of arousal from NREM sleep and related to anomalous SWS and SWA. Power spectral analyses have never been used to quantify patients' SWA across sleep cycles. N/A SETTING: N/A PATIENTS: A polysomnographic study was performed on 15 adult sleepwalkers and 15 age- and sex-matched controls. N/A MEASUREMENTS & RESULTS: Sleepwalkers had a significantly greater number of awakenings from SWS than did control subjects. Controls showed a greater decrease in SWA across NREM cycles. Sleepwalkers had a significantly lower level of SWA during the first NREM period, where most awakenings take place. Sleepwalkers appear to suffer from an abnormality in the neural mechanisms responsible for the regulation of SWS.

Temporal Characteristics of Delta Activity During NREM Sleep in Depressed Outpatients and Healthy Adults: Group and Sex Effects

The primary aim was to evaluate group and sex differences in delta activity across non-rapid eye movement (NREM) sleep in depressed patients and healthy controls. Repeated-measures ANOVA contrasted delta power, amplitude and incidence in the first three NREM periods (stages 2, 3, and 4) of sleep. The time course of delta activity was evaluated with exponential regressions. Age effects on delta were evaluated with linear regression analysis. Two consecutive nights were spent in the laboratory, the first of which served as adaptation. Twenty-two (9 men, 13 women) symptomatic, but unmedicated, outpatients with major depressive disorder (MDD) and 23 healthy controls (15 men, 8 women) participated in the study. Delta power and amplitude showed significant group by sex interactions. Men with MDD showed lower power and amplitude in NREM sleep compared to women with MDD, but did not differ significantly from controls. However, the time course of delta power and amplitude was significantly different in men with MDD, with lower accumulation and slower dissipation across NREM sleep than all other groups. Women with MDD showed no evidence of lower delta power and amplitude or an abnormal time course compared to control women or men. Age had a differential influence on delta activity between the groups, with little age-related change in delta activity in the depressed groups. It was concluded that slow-wave sleep deficiencies may be characteristic of men, but not women, with MDD. It was also concluded that the influence of age on delta activity varied as a function of both psychiatric status and sex.

Slow-wave activity in NREM sleep: sex and age effects in depressed outpatients and healthy controls

The amplitude and time course of slow-wave activity (SWA) during NREM sleep were compared in 76 outpatients with depression and 55 healthy control subjects. Lower SWA amplitude was evident in the depressed group, especially among depressed men. For the most part, significant differences between patients and control subjects were restricted to the first NREM period and only in those 20–30 years of age. Significant age-related declines in SWA amplitude were evident in control subjects but not in depressed patients. In addition, sex differences in the depressed group were twice as large as those seen in control subjects. The time course of SWA amplitude, presumed to reflect homeostatic sleep regulation of SWA, was only abnormal in depressed men with lower accumulation and slower dissipation over NREM sleep. Depressed women showed no evidence of an abnormal SWA time course. Furthermore, no sex differences in the time course of SWA were evident in control subjects, and age-related changes in this aspect of regulation were not striking in any group. Thus, the amplitude of SWA showed strong age effects in healthy individuals but not in those with MDD whereas the time course showed very subtle age effects. It was suggested that men, but not women, with MDD show impaired SWA regulation that is evident from 20 to 40 years of age. These findings provide further support that the pathophysiology of depression differs for men and women and suggest that maturational effects on SWA in depression differ from those observed in healthy individuals.

Towards a neurobiology of dysfunctional arousal in depression: the relationship between beta EEG power and regional cerebral glucose metabolism during NREM sleep

This study sought to clarify the neurobiological basis of variations in one aspect of central nervous system ‘arousal’ in depression by characterizing the functional neuroanatomic correlates of beta electroencephalographic (EEG) power density during non-rapid eye movement (NREM) sleep. First, nine healthy ( n=9) subjects underwent concurrent EEG sleep studies and [ 18F]2-fluoro-2-deoxy- d-glucose ([ 18F]FDG) positron emission tomography (PET) scans during their first NREM period of sleep in order to generate hypotheses about specific brain structures that show a relationship between increased beta power and increased relative glucose metabolism. Second, brain structures identified in the healthy subjects were then used as a priori regions of interest in similar analyses from identical studies in 12 depressed subjects. Statistical parametric mapping was used to identify the relationship between beta power and relative regional cerebral glucose metabolism (rCMRglu) during NREM sleep. Regions that demonstrated significant correlations between beta power and relative cerebral glucose metabolism in both the healthy and depressed subjects included the ventromedial prefrontal cortex and the right lateral inferior occipital cortex. During a baseline night of sleep, depressed patients demonstrated a trend toward greater beta power in relation to a separate age- and gender-matched healthy control group. In both healthy and depressed subjects, beta power negatively correlated with subjective sleep quality. Finally, in the depressed group, there was a trend for beta power to correlate with an indirect measure of absolute whole brain metabolism during NREM sleep. This study demonstrates a similar relationship between electrophysiological arousal and glucose metabolism in the ventromedial prefrontal cortex in depressed and healthy subjects. Given the increased electrophysiological arousal in some depressed patients and the known anatomical relations between the ventromedial prefrontal cortex and brain activating structures, this study raises the possibility that the ventromedial prefrontal cortex plays a significant role in mediating one aspect of dysfunctional arousal found in more severely aroused depressed patients.

Relationship between rapid eye movement sleep and testosterone secretion in normal men.

The relation between the pituitary-gonadal hormones' rhythm and sleep physiology in men is not fully elucidated. To examine whether the reproductive hormones are correlated with sleep architecture, we determined the nocturnal serum levels of testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) in six healthy young men. Serum hormone levels were obtained every 15 minutes from 1900 to 0700 hours with simultaneous polysomnographic sleep recordings. Hourly testosterone levels were lowest when subjects were awake (1900-2200 hours) than during sleep (2300-0700 hours). Testosterone nocturnal rise antedated the first REM by about 90 minutes. The rise in testosterone levels was slower when REM latency was longer. Mean nocturnal testosterone levels did not correlate with the number of rapid eye movement (REM) episodes. Also, pre-non-REM (NREM) testosterone levels were higher as compared with the pre-REM periods and lower during the first NREM period as compared with other nocturnal NREM periods. Serum LH levels disclosed a nocturnal rise that preceeded a similar rise in testosterone by about an hour. We conclude that in young adult men, testosterone levels begin to rise on falling asleep, peak at about the time of first REM, and remain at the same levels until awakening.

Electroencephalographic sleep correlates of episode and vulnerability to recurrence in depression

The study of electroencephalogram (EEG) sleep in depressed patients before and after treatment with psychotherapy can distinguish episode-related and persistent biological features. With longitudinal follow-up, we can also assess whether EEG sleep measures are associated with recurrence of depression. In the current study, we examined EEG sleep during the depressed state and during symptomatic remission after treatment with interpersonal psychotherapy in 42 outpatients with major depression. Analyses included both visually-scored and computer-analyzed measures. Patients showed significant increases in sleep latency (p = .01) and rapid eye movement (REM) latency (p = .04) from baseline to remission, as well as a decrease in REM sleep percent (p = .03). Total delta EEG counts decreased from baseline to remission (p = .03), specifically in the second nonrapid eye movement (NREM) period (p = .03); as a result, the relative distribution of delta activity shifted toward sleep onset (i.e., increased delta sleep ratio; p = .03). Automated REM counts also decreased from depression to remission (p = .006). Compared to patients who remained well through one year of follow-up, those who suffered a recurrence of depression had less delta EEG activity at baseline and remission (p = .01), particularly in the lowest delta frequency band of 0.5-1.0 Hz. Specific components of sleep (total delta activity, delta ratio, REM activity) constitute episode-related biological features. Other components (slowest delta activity) may represent vulnerability factors for recurrence.

Flunitrazepam effects on human sleep eeg spectra II: Sigma and beta alterations during NREM sleep

Flumtrazepam (FNZ) is known to enhance the higher EEG frequencies, including sigma (10–15 Hz) and beta (20–28 Hz). Both sigma and beta frequency bands show an inverse relationship with delta (0.3–3 Hz) during NREM periods, as we have previously reported. It is not known whether generation of these two EEG frequencies is mediated by the same or different neuronal mechanisms. In this report, we compare alterations of delta, sigma and beta EEG induced by FNZ (4 mg) orally administered to five healthy male subjects for seven consecutive nights. Sleep EEG on the baseline night (BLN), and the fourth and seventh drug nights (4DN, 7DN) was subjected to fast Fourier transform (FFT) analysis. On drug nights, sigma was enhanced without regard to delta amount, but beta was enhanced only during epochs containing low delta. Thus, sigma and beta EEG were altered differently by the same pharmacological agent. These results suggest that sigma and beta EEG are mediated by different neuronal mechanisms.

Sleep EEG analysis by linear prediction: frequency changes of slow-wave activity within NREM and REM sleep episodes in healthy men.

The linear prediction method was applied to obtain a power spectra estimate of sleep EEG in 10 healthy young men. In order to analyze frequency changes of the slow-wave activity (EEG power in the delta band, 0.05-2.88 Hz), the delta mean frequency was computed for each 20-second sleep epoch. A mean delta mean frequency was calculated for each sleep stage in each individual. Our observations indicate that the delta mean frequency decreases during NREM periods and increases mainly at the onset of the REM episodes. This finding, in parallel with the detailed analysis of slow-wave power variations, leads to an additional description of sleep characteristics during transitions between the NREM-REM sleep episodes.

Trends in Electroencephalographic Synchronization Across Nonrapid Eye Movement Sleep in Infants

The trend of synchronized (high-voltage, low-frequency) electroencephalographic (EEG) activity was determined across nonrapid eye movement (NREM) sleep periods of night sleep in two groups of infants (eight "young infants", age 2-19 weeks; eight "older infants", age 21-54 weeks) and, a reference, in a group of eight adults (age 16-45 years). By automatic analysis of the sleep EEG, a parameter was derived that represents the degree of synchronized (high-amplitude, low-frequency) EEG activity for successive 30-second epochs. For each subject, the average level of EEG synchronization for each NREM period and the time of the NREM period midpoints were determined. In all three groups, synchronized EEG activity tended to decrease across successive NREM periods. This trend was weaker for infants than for adults and, surprisingly, weaker for older than for young infants. This suggests that the decreasing trend typical for adults is already present in the first months after birth. The difference in trend between infants and adults may be caused by differences in the 24-hour sleep-wakefulness distribution, whereas the distinction between young and older infants could be related to a restructuring of sleep in the second semester, in particular to the emergence of slow-wave sleep and its peculiar distribution across NREM periods of night sleep.

A New Paradigm for Dream Research: Mentation Reports Following Spontaneous Arousal from REM and NREM Sleep Recorded in a Home Setting

The "Nightcap," a relatively nonintrusive and "user-friendly" sleep monitoring system, was used by 11 subjects on 10 consecutive nights in their homes. Eighty-eight sleep mentation reports were obtained after spontaneous awakenings from Nightcap-identified REM sleep and 61 were obtained from NREM awakenings. Sleep mentation was recalled in 83% of REM reports and 54% of NREM reports. The median length of REM reports was 148 words compared to 21 words for NREM reports. Twenty-four percent of the REM reports were over 500 words long; no NREM reports over 500 words were obtained. REM report lengths were lowest during the first 15 min of the REM cycle and longest 15–45 min into the period. In contrast, 7 of the 9 NREM reports more than 100 words long occurred within the first 15 min of NREM periods. The Nightcap thus appears to be an effective and efficient method of collecting large numbers of sleep mentation reports with correlated sleep staging under normal ecological conditions.