The mismatch negativity to frequency deviant stimuli during natural sleep

Eight subjects spent a single night in the sleep laboratory. Event-related potentials (ERPs) were recorded during the presentation of two auditory "oddball' stimulus conditions in which tonal frequency was manipulated. In the first condition, 1000 Hz "standard' and 2000 Hz "deviant' tones were presented. In the second condition, the deviant tone was reduced to 1050 Hz. In both conditions, deviant probability was 0.2. Stimuli were presented every 600 ms during wakefulness and stages 2, 4, and REM of sleep. A distinctive N1 wave was visible in both stimulus conditions when the subject was awake. The deviant stimuli elicited a "mismatch negativity' (MMN) that inverted in polarity at the mastoid. In REM sleep, an N1 and a MMN were also elicited in both conditions. In the large deviance condition, the MMN had a slightly attenuated amplitude and was shorter in duration while in the small deviant condition, its peak latency was unusually early. Neither the N1 nor the MMN could be recorded in non-REM sleep.     

Respiratory and body movements as indicators of sleep stage and wakefulness in infants and young children

Conventional polysomnographic (PSG) sleep staging to sleep staging based on a static-charge-sensitive bed (SCSB) recording in infants and young children was compared. The study consisted of whole-night clinical sleep studies in 22 children at 24 weeks (SD 24, range 1-79 weeks) of age. Most of the children presented with respiratory disturbances during sleep. From the SCSB record, sleep stages were differentiated according to regularity of breathing, presence of body movements, and most important, presence of high-frequency components of breathing (SCSB spikes). With both methods, three sleep/wake stages were distinguished: rapid eye movement (REM) sleep, non-rapid eye movement (NREM) sleep and wakefulness. The average interscorer reliability of the PSG sleep staging controlled in nine subjects was 88%. The average concordance between the two methods ranged from 82 to 85%, depending on the criteria used for scoring the SCSB. The mean sensitivity of the SCSB to detect NREM sleep ranged from 77 to 90% and the mean sensitivity to detect REM sleep ranged from 61 to 86%. The mean positive predictive value was 89-96% for NREM sleep and 54-67% for REM sleep. In conclusion, REM sleep is characterized by irregular breathing with superimposed fast respiratory movements. These changes are specific enough to allow distinction between episodes of NREM sleep, REM sleep and wakefulness with the non-invasive SCSB method in infants and young children. Incomplete concordance between PSG and SCSB score was most frequently observed during sleep stage transition periods, where the behavioural state and electrophysiological criteria disagreed. When combined with the PSG, the SCSB provides complementary information about the behavioural state of child.     

Predicting duration of sleep from the three process model of regulation of alertness

OBJECTIVES: Irregular working hours severely disturb sleep and wakefulness. This paper presents a modification of the quantitative (computerised) three process model of regulation of alertness to predict duration of sleep in connection with irregular sleep patterns. METHODS: The model uses a circadian "C" (sinusoidal) and homeostatic "S" (exponential) component (the duration of previous periods awake and asleep), which are summed to yield predicted alertness (on a scale of 1-16). It assumes that waking from sleep will occur at a given alertness level (S' + C') when recuperation is complete. Variables of electroencephalographic duration of sleep from two studies of irregular sleep were used to model the S and C variables in a regression approach to maximise prediction. The model performance was cross validated against published field and laboratory data. RESULTS: The model parameters were defined with a high degree of precision R2 = 0.99 and the validation yielded similar values R2 = 0.98-0.95, depending on the acrophase. The paper also describes a simplified graphical version of the computation model seen as a two dimensional duration of sleep nomogram. CONCLUSION: The model seems to predict group means for duration of sleep with high precision and may serve as a tool for evaluating work and rest schedules to reduce risks of sleep disturbances.     

Absence of tonic electromyographic activity during sleep in normal and spastic nonmimetic skeletal muscles in man

An electromyographic study of nonmimetic skeletal muscles was carried out in 8 normal adults and 4 patients with spastic hemiparesis during all stages of sleep for a total of 21 nights. All normal subjects showed absence of tonic electromyographic activity in all nonmimetic skeletal muscles in all stages of sleep. Also, during quiet, relaxed wakefulness, tonic muscle discharges disappeared in the normal subjects. Three patients with upper motor neuron spasticity demonstrated results during sleep similar to those obtained in the normal subjects. In the fourth patient, tonic muscle discharges persisted into stage 2 non-REM sleep, disappeared within 30 to 240 seconds following the onset of stage 2 sleep, and were absent during stages 3 and 4 sleep and REM sleep.     

Influence of sleep states on laryngeal and abdominal muscle response to upper airway occlusion in lambs

This study was aimed at describing abdominal and laryngeal muscle responses to upper airway occlusion (UAO) in early life and the effect of sleep states on these responses. Twelve nonsedated, 9-26-d-old lambs were studied. We simultaneously recorded 1) airflow (pneumotachograph + face mask); 2) sleep states (electrocorticogram and electrooculogram); 3) abdominal muscle (external obliquus) electromyogram (EMG); and 4) glottic constrictor (thyroarytenoid) and dilator (posterior cricoarytenoid and cricothyroid) muscle EMGs. The pneumotachograph was repeatedly occluded for 15-30 s in wakefulness and natural sleep. We analyzed 90 occlusions during wakefulness (11 lambs), 28 during non-rapid eye movement (nREM) sleep (six lambs), and 23 during rapid eye movement (REM) sleep (five lambs). A phasic expiratory external obliquus EMG was present during baseline and progressively increased throughout UAO in wakefulness and nREM sleep, but not in REM sleep. Phasic thyroarytenoid EMG progressively increased during inspiratory efforts throughout UAO in wakefulness and nREM sleep, paralleling the increase in glottic dilator (posterior cricoarytenoid and cricothyroid) EMG. In contrast, glottic muscle response to UAO in REM sleep was severely blunted or disorganized by frequent swallowing movements. We conclude that UAO triggers complex and coordinated laryngeal and abdominal muscle responses during wakefulness and nREM sleep in lambs; these responses are largely absent, however, in REM sleep. These unique results, together with the defective arousal response in REM sleep, suggest that vulnerability to airway occlusion could be increased during REM sleep in early life. Possible implications for understanding severe postnatal apneas are discussed.     

State-related changes in upper airway caliber and surrounding soft-tissue structures in normal subjects

State-dependent changes in upper airway caliber were studied with magnetic resonance imaging (MRI) techniques. We hypothesized that changes in airway caliber during sleep in normal subjects would result from positional and dimensional changes in upper airway soft-tissue structures, including the lateral pharyngeal walls, tongue, and soft palate. We used MRI to study 15 normal subjects during wakefulness and sleep. Sleep was facilitated by one night of sleep deprivation prior to MRI. During sleep, the volume of the retropalatal (RP) airway was reduced by 19% (p = 0.03). The volume of the retroglossal (RG) airway was not significantly reduced during sleep, suggesting that the RP region may be more likely to collapse. The mean minimal cross-sectional airway area was reduced by 228% (p = 0.004) in the RP and by 22% (p = 0.02) in the RG region during sleep as compared with values in anatomically matched axial images during wakefulness. Airway anteroposterior (AP) and lateral dimensions were also significantly reduced in the RP region. Airway narrowing in the RP region was associated with a 7% increase in thickness of the lateral pharyngeal walls (p = 0.04). In nine subjects, sagittal data showed significant posterior displacement of the soft palate during sleep as compared with wakefulness. Multiple linear regression analyses indicated that reduction in the RP airway area during sleep resulted from posterior movement of the soft palate, thickening of the lateral pharyngeal walls, and an increase in tongue oblique distance. We conclude that the lateral pharyngeal walls play an important role in upper airway narrowing during sleep in normal subjects.     

Respiratory-related pharyngeal constrictor muscle activity in normal human adults

Electromyographic activity of the superior, middle, and inferior pharyngeal constrictor (PC) muscles was examined in 10 normal adult humans during wakefulness and sleep. Wire electrodes were inserted close to the midline of the posterior pharyngeal wall at the level of the soft palate (superior PC), tip of the epiglottis (middle PC), and corniculate tubercle (inferior PC). In general, the three PC muscles exhibited similar patterns of activation. The PCs were activated during swallows, repetitive "pa" sounds, changes in head position, and the last portions of slow inspiratory and expiratory vital capacity maneuvers. Respiratory-related PC activity was infrequent during quiet breathing during wakefulness; variable and inconsistent phasic activation in expiration in one or more of the PCs was present in seven of the 10 subjects, particularly after a swallow. Progressive hyperoxic hypercapnia and progressive isocapnic hypoxia were associated with recruitment of phasic PC activity, which was predominantly expiratory; however, variable discharge patterns were observed within a given muscle and a given subject. When phasic PC activity was present, preactivation during late inspiration was frequently observed. PC activity was absent in NREM sleep and exhibited sporadic, nonrespiratory-related bursts of activity during REM sleep. Passively induced hypocapnic hyperventilation in NREM sleep was not associated with PC activation. The results indicate that the PCs have very similar patterns of activation and exhibit phasic expiratory activity during relatively high ventilatory output states in wakefulness.     

Effects of NREM sleep on dynamic within-breath changes in upper airway patency in humans

The purpose of our study was to compare inspiratory- and expiratory-related changes in retropalatal cross-sectional area (CSA) during wakefulness to those during non-rapid-eye-movement (NREM) sleep. We studied 18 subjects in whom the severity of sleep-disordered breathing varied. Relative changes in CSA were visualized by using fiber-optic endoscopy. For each breath analyzed (wakefulness n = 4-13; sleep n = 7-16), the CSA was measured at fixed points within inspiration and expiration (0, 25, 50, and 100% of the inspiratory and expiratory duration); these measurements were expressed as a percentage of the CSA that occurred at the start of inspiration. During wakefulness, there was a statistically significant increase in the retropalatal CSA (compared with the start of inspiration) only during early expiration (group mean: expiration, 0% = 112.6 +/- 3.2 (SE) %; 25% = 122.8 +/- 6.2%; 50% = 110.6 +/- 3.8%). In contrast, during sleep, significant changes in CSA occurred during both inspiration and expiration (group mean: inspiration, 25% = 75.3 +/- 6.0%; 50% = 66.7 +/- 7.7%; 75% = 64.6 +/- 8.1%; expiration, 0% = 126.8 +/- 11.8%; 25% = 125.3 +/- 6.9%). The expiratory-related increase in CSA was followed by narrowing such that at end expiration the caliber of the airway was returned to that occurring at the beginning of inspiration (group mean at end expiration = 98.6 +/- 3.1%). The largest changes in CSA occurred in the subjects with an increased body mass index (BMI). We conclude that, during NREM sleep, significant changes in CSA occur during both inspiration and expiration and that the magnitude of these changes is significantly influenced by BMI.     

Topographic analysis of coherence and propagation of EEG activity during sleep and wakefulness

Overnight sleep EEG recorded from 21 derivations was studied in 8 healthy subjects. The vector autoregressive model was fitted to all 21 channels simultaneously. Ordinary, multiple and partial coherences and directed transfer functions were estimated for sleep stages and wakefulness. Ordinary coherences give rather trivial information that coherence decreases with distance. Partial coherences revealed specific structure that was well repeatable for the subjects studied. Differences in coherence patterns between sleep stages were found by means of statistical tests. An increase of coherence was found for sleep stages 2, 3 and 4. Directed transfer function made possible the identification of the main centers from which EEG activity is spreading during sleep and wakefulness. During sleep the influence of subcortical structures was manifested by propagation of activity from the fronto-central region. The range of this interaction was highest in sleep stages 3 and 4. An EEG analysis, based on the approach of treating time series as a realization of one process and on the simultaneous (not pair-wise) evaluation of signals offers new possibilities in the investigation of synchronization and functional relations in the brain.     

Frontal Electroencephalogram Alpha Asymmetry During Sleep: Stability and Its Relation to Affective Style.

Electroencephalogram (EEG) alpha (8-12 Hz) asymmetries were collected from the mid-frontal and central regions during presleep wakefulness and Stage 1, Stage 2, and rapid eye movement (REM) sleep in 11 healthy right-handed participants who were free of psychiatric, neurological, and sleep problems. The authors found significant correlations between presleep wakefulness and different stages of sleep in the frontal, but not central, EEG alpha asymmetry measure. The strongest correlation was between presleep waking and REM sleep, replicating and extending relation earlier work to a normal population. The high degree of association between presleep waking and REM sleep may be a result of high cortical activation common to these states and may reflect a predisposition to different styles of emotional reactivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in the extracellular matrix on the surface of sintered bovine bone implanted in the femur of a rabbit: an immunohistochemical study

The neuroanatomical substrates controlling and regulating sleeping and waking, and thus consciousness, are located in the brain stem. Most crucial for bringing the brain into a state conducive for consciousness and information processing is the mesencephalic part of the brain stem. This part controls the state of waking, which is generally associated with a high degree of consciousness. Wakefulness is accompanied by a low-amplitude, high-frequency electroencephalogram, due to the fact that thalamocortical neurons fire in a state of tonic depolarization. Information can easily pass the low-level threshold of these neurons, leading to a high transfer ratio. The complexity of the electroencephalogram during conscious waking is high, as expressed in a high correlation dimension. Accordingly, the level of information processing is high. Spindles, and alpha waves in humans, mark the transition from wakefulness to sleep. These phenomena are related to drowsiness, associated with a reduction in consciousness. Drowsiness occurs when cells undergo moderate hyperpolarizations. Increased inhibitions result in a reduction of afferent information, with a lowered transfer ratio. Information processing subsides, which is also expressed in a diminished correlation dimension. Consciousness is further decreased at the onset of slow wave sleep. This sleep is controlled by the medullar reticular formation and is characterized by a high-voltage, low-frequency electroencephalogram. Slow wave sleep becomes manifest when neurons undergo a further hyperpolarization. Inhibitory activities are so strong that the transfer ratio further drops, as does the correlation dimension. Thus, sensory information is largely blocked and information processing is on a low level. Finally, rapid eye movement sleep is regulated by the pontine reticular formation and is associated with a "wake-like" electroencephalographic pattern. Just as during wakefulness, this is the expression of a depolarization of thalamocortical neurons. The transfer ratio of rapid eye movement sleep has not yet been determined, but seems to vary. Evidence exists that this type of sleep, associated with dreaming, with some kind of perception and consciousness, is involved in processing of "internal" information. In line with this, rapid eye movement sleep has higher correlation dimensions than slow-wave sleep and sometimes even higher than wakefulness. It is assumed that the "near-the-threshold" depolarized state of neurons in the thalamus and cerebral cortex is a necessary condition for perceptual processes and consciousness, such as occurs during waking and in an altered form during rapid eye movement sleep.     

Adenosine: a mediator of the sleep-inducing effects of prolonged wakefulness

Both subjective and electroencephalographic arousal diminish as a function of the duration of prior wakefulness. Data reported here suggest that the major criteria for a neural sleep factor mediating the somnogenic effects of prolonged wakefulness are satisfied by adenosine, a neuromodulator whose extracellular concentration increases with brain metabolism and which, in vitro, inhibits basal forebrain cholinergic neurons. In vivo microdialysis measurements in freely behaving cats showed that adenosine extracellular concentrations in the basal forebrain cholinergic region increased during spontaneous wakefulness as contrasted with slow wave sleep; exhibited progressive increases during sustained, prolonged wakefulness; and declined slowly during recovery sleep. Furthermore, the sleep-wakefulness profile occurring after prolonged wakefulness was mimicked by increased extracellular adenosine induced by microdialysis perfusion of an adenosine transport inhibitor in the cholinergic basal forebrain but not by perfusion in a control noncholinergic region.     

Brain networks affected by synchronized sleep visualized by positron emission tomography

Nineteen lightly sleep-deprived healthy volunteers were examined with H2(15)O and positron emission tomography (PET). Scanning was performed during wakefulness and after the subjects had fallen asleep. Sleep stage was graded retrospectively from electroencephalogram (EEG) recordings, and scans were divided into two groups: wakefulness or synchronized sleep. Global flow was quantified, revealing no difference between sleep and wakefulness. A pixel-by-pixel-blocked one-way analysis of variance (ANOVA) was performed after correcting for differences in anatomy and global flow. The sum of squares of the z-score distribution showed a highly significant (P < 0.00001) omnibus difference between sleep and wakefulness. The z-score images indicated decreased flow in the thalamus and the frontal and parietal association cortices and increased flow in the cerebellum during sleep. A principal component (PC) analysis was performed on data after correction for global flow and block effects, and a multivariate analysis of variance (MANOVA) on all PC scores revealed significant (P = 0.00004) differences between sleep and wakefulness. Principal component's 2 and 5 correlated to sleep and revealed distinct networks consisting of PC 2, cerebellum and frontal and parietal association cortices, and PC 5, thalamus.     

Induction of visual imagery during NREM sleep

In an attempt to induce eye movements (EMs) in non-rapid eye movement sleep, light and sound stimuli were presented to human subjects (at below-waking threshold) during stage 2 sleep. EMs were used as an indicator of ponto-geniculo-occipital (PGO) wave activity. When at least one concurrent EM in response to the stimuli was observed, the subjects were awakened and mentation reports collected. Compared to equivalent control periods with no stimulation, awakenings from the stage 2 stimulation condition showed a higher frequency of visual imagery reports, electroencephalogram alpha activity, and k-complexes. Additional control and stimulation conditions elicited from rapid eye movement sleep awakenings showed no significant differences in the frequency of visual imagery reports. When the amount of alpha activity before stage 2 awakenings from which imagery was reported was compared to that from which imagery was not reported, imagery awakenings showed significantly more alpha. Results can be interpreted as evidence for a link between PGO activity and dreaming in humans or in terms of an arousal-window hypothesis of visual hallucinations.     

Changes in EEG power density during sleep laboratory adaptation

First- and second-night effects on the electroencephalogram (EEG) were investigated by means of polygraphic sleep recordings and all-night spectral analysis. Eighteen normal subjects were studied for three consecutive nights in a hospital sleep laboratory. Visual sleep scoring showed that there was a first-night effect in normal subjects similar to that reported previously [increased wakefulness; decreased total sleep time, sleep efficiency, and rapid eye movement (REM) sleep]. Spectral analysis of the sleep EEG revealed important changes, most of which occurred in REM sleep. Increased delta, theta, and beta1 power densities accompanied by decreased mean frequency were seen in REM sleep in the second night. On the basis of REM sleep deprivation results previously published, our data suggest that the second night could be affected by partial REM sleep deprivation that occurred in the first night. Delta and theta power density values decreased in the first non-rapid eye movement episode of nights 1 and 2; this could result from increased REM sleep pressure. The overall consistency of spectral data in the first and second night with REM sleep findings derived from visual scoring in the first night lends further support to this hypothesis. The sleep disturbance experienced during the first night in a sleep laboratory may be a useful and valid model of transient insomnia. Therefore, we conclude that data from all nights recorded should be included in assessing a subject's sleep.     

Use of dynamic two-dimensional transesophageal echocardiography for renal cell carcinoma with cavoatrial tumor thrombus

Previous investigations involving continuous blood pressure (BP) monitoring have shown an important alteration of the 24-hour BP profile in patients with obstructive sleep apnea syndrome (OSAS). We investigated the impact of REM sleep on the 24-hour BP cycle in 16 severe OSAS male patients (mean respiratory disturbance index = 66 +/- 16 events/hour of sleep), with hypertension (mean BP 162 +/- 21/105 +/- 11 mmHg World Health Organization (WHO) protocol). Two successive nights of polysomnography were performed, and arterial BP was monitored continuously during the second 24-hour period after brachial artery cannulation. During the daytime, subjects were kept awake and supine. At 3 p.m. BP was continuously monitored during quiet supine wakefulness for 20 minutes. Systolic, diastolic and mean BP and heart rate (HR) were analyzed and tabulated in mean values of 5 minute segments. Sleep/wake information were correlated with cardiovascular variables. Each uninterrupted REM sleep period was identified and comparison between the period of quiet supine wakefulness and REM sleep HR and BP values was performed. 8 OSAS patients presented a normal drop of the mean arterial BP during the nocturnal REM sleep periods compared to quiet supine wakefulness (mean value = -10.8 +/- 7.3 mmHg) ("dippers") while the other 8 subjects ("REM sleep non dippers"), revealed an elevated mean arterial BP during REM sleep (mean value = 18.9 +/- 10.9 mm Hg). The absence of the normal circadian BP dip seen during the nocturnal sleep period is considered as an indication of vascular risk. The REM sleep non dipping may play a role in this risk.     

Calbindin-D 28 kD and parvalbumin in the horizontal cells of rat retina during development

Restless legs syndrome (RLS) and periodic limb movements in sleep (PLMS) are disorders that are common and disturbing to uremic patients. The treatment of these is problematic. Eight patients on chronic hemodialysis and continuous peritoneal dialysis completed a double-blind placebo-controlled crossover study using incremental doses of pergolide up to 0.25 mg at bedtime for treatment of RLS and sleep disruption. Five patients (62.5%) noted subjective improvement in restless legs symptoms and sleep quality. Objective results were improved only slightly by treatment. The percentage of the first hour in bed during which leg movements occurred decreased from 20.5 +/- 6.0 to 11.5 +/- 3.3, p < 0.05. However, findings during sleep were less positive. The following measures were not significant between placebo and treatment: leg movements per hour of sleep [53.7 +/- 22.3 vs 35.8 +/- 11.8 (p = 0.2)]; and percentage of sleep time spent with leg movements [5.5% +/- 3.2 vs 4.4% +/- 1.4 (p = 0.37)]. Patients continued to have very disrupted sleep, and we could not document an objective improvement in sleep architecture. Thus, although pergolide at the dose of 0.25 mg at bedtime provided subjective improvement in symptoms of restless legs and quality of sleep, and objectively decreased leg movements during the first hour in bed, objectively sleep continued to be disrupted. In this small patient group, the response to pergolide was not uniform, and further investigation is required to test effectiveness at higher doses.     

Compensatory sleep responses to wakefulness induced by the dopamine autoreceptor antagonist (-)DS121

The effect of the dopamine autoreceptor antagonist (-)DS121 on wakefulness, locomotor activity, body temperature and subsequent compensatory sleep responses was examined in the rat. Animals entrained to a light-dark cycle were treated at 5 h after lights-on (CT-5) with 0.5, 1, 5 or 10 mg/kg i.p. (-)DS121 or methylcellulose vehicle. An additional group received 5 mg/kg i.p. (-)DS121 or vehicle 6 h after lights-off (CT-18). At CT-5, (-)DS121 dose-dependently increased wakefulness, locomotor activity and body temperature, and decreased both non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM) during the first 4 h post-treatment relative to vehicle controls. REM interference lasted up to 3 h longer than NREM. Low doses of (-)DS121 (0.5 and 1 mg/kg) produced relatively little waking that was not followed by significant compensatory sleep responses. In contrast, higher doses (5 and 10 mg/kg) produced compensatory hypersomnolence (robust increases in NREM immediately after the primary waking effect) that was proportional to the duration of drug-induced wakefulness. NREM recovery 24 h post-treatment was the same for the 5 mg/kg (65.4 +/- 9.9 min) and 10 mg/kg (64.8 +/- 9.3 min) doses, but was not proportional to prior wake duration. NREM displaced by drug-induced wakefulness was recovered completely by 24 h post-treatment at the 5 mg/kg dose, but only 63.5% recovered at 10 mg/kg. In contrast, equivalent wakefulness produced by sleep deprivation yielded 100% NREM recovery. At CT-18, (-)DS121 (5 mg/kg) increased wakefulness without disproportionately increasing locomotor activity, and was compensated fully by 24 h post-treatment. These data show that (-)DS121 dose-dependently increases wakefulness, which is followed by hypersomnolence that is proportional to drug-induced wake-promoting efficacy.     

A finger-tapping task and a reaction time task as behavioral measures of the transition from wakefulness to sleep: which task interferes less with the sleep onset process

The aim of this study was to assess whether a finger-tapping task (FTT), in which normal subjects repeatedly tap on a button while falling asleep, could be less disturbing and provide comparable information on the sleep onset period (SOP) with respect to a reaction-time task (RTT) to acoustic stimuli, in which the onset of sleep can be delayed by the arousing effect of the acoustic stimuli. Twelve subjects slept at their homes and six slept in a sleep laboratory for four consecutive nights. After one adaptation night and one baseline night, subjects were required to fall asleep in the third and fourth nights, bimanually performing either a RTT or a FTT. The results indicate that the FTT interfaces less with the SOP compared to the RTT and suggest that the FTT provides further advantages as a behavioral measure of the transition from wakefulness to sleep. In fact, the tapping task is associated with significantly shorter behavioral and polysomnographic sleep onset latencies and with a greater proportion of slow-wave sleep (SWS) during the transition from wakefulness to sleep compared with the RTT. Furthermore, correlations among subjective, behavioral, and electroencephalograph (EEG) latencies confirm the validity of the finger-tapping task as a behavioral measure of sleep onset.     

Polysomnographic sleep measures in patients with uremic and idiopathic restless legs syndrome

In the present study, the nocturnal electroencephalographic sleep pattern, the number of periodic leg movements (PLM) during sleep and wakefulness, and the subjective sleep parameters of patients with uremic (n = 10) and idiopathic (n = 17) restless legs syndrome (RLS) were compared. The main finding was that the total number of PLM (p = 0.019), the PLM index (p = 0.018), and the PLM index while awake (p = 0.003) were significantly higher in patients with uremic RLS compared with patients who had idiopathic RLS. Additionally, both groups showed a distinct time-of-night pattern of PLM activity. Polysomnographic measures of sleep continuity (total sleep time, sleep efficiency, sleep onset latency, time awake) and sleep architecture (amount of nonrapid eye movement sleep stages 1, 2, 3, and 4 and the amount of rapid eye movement sleep) did not differ between uremic and idiopathic RLS patients. With regard to subjective parameters, sleep quality was estimated to be worse in uremic RLS (p = 0.033), whereas other parameters (for example, severity of RLS, quality of life) did not differ between the two groups. It is suggested that uremia itself worsens the motor symptoms of RLS, probably as a result of increased excitability.