Maxime Elbaz

Disruption of hierarchical predictive coding during sleep

Significance Sleeping disrupts the conscious awareness of external sounds. We investigated the stage of processing at which this disruption occurs. In the awake brain, when a regular sequence of sounds is presented, a hierarchy of brain areas uses the available regularities to predict forthcoming sounds and to respond with a series of “prediction error” signals when these predictions are violated. Using simultaneous recordings of electroencephalography and magnetoencephalography signals, we discovered that both short-term and long-term brain responses to auditory prediction errors are disrupted during non-rapid eye movement and rapid eye movement sleep; however, the brain still exhibits detectable auditory responses and a capacity to habituate to frequently repeated sounds. Thus, sleep appears to selectively affect the brain’s prediction and error detection systems. When presented with an auditory sequence, the brain acts as a predictive-coding device that extracts regularities in the transition probabilities between sounds and detects unexpected deviations from these regularities. Does such prediction require conscious vigilance, or does it continue to unfold automatically in the sleeping brain? The mismatch negativity and P300 components of the auditory event-related potential, reflecting two steps of auditory novelty detection, have been inconsistently observed in the various sleep stages. To clarify whether these steps remain during sleep, we recorded simultaneous electroencephalographic and magnetoencephalographic signals during wakefulness and during sleep in normal subjects listening to a hierarchical auditory paradigm including short-term (local) and long-term (global) regularities. The global response, reflected in the P300, vanished during sleep, in line with the hypothesis that it is a correlate of high-level conscious error detection. The local mismatch response remained across all sleep stages (N1, N2, and REM sleep), but with an incomplete structure; compared with wakefulness, a specific peak reflecting prediction error vanished during sleep. Those results indicate that sleep leaves initial auditory processing and passive sensory response adaptation intact, but specifically disrupts both short-term and long-term auditory predictive coding.

In flight automatic detection of vigilance states using a single EEG channel

Sleepiness and fatigue can reach particularly high levels during long-haul overnight flights. Under these conditions, voluntary or even involuntary sleep periods may occur, increasing the risk of accidents. The aim of this study was to assess the performance of an in-flight automatic detection system of lowvigilance states using a single electroencephalogram channel. Fourteen healthy pilots voluntarily wore a miniaturized brain electrical activity recording device during long-haul flights (10 ± 2.0 h, Atlantic 2 and Falcon 50 M, French naval aviation). No subject was disturbed by the equipment. Seven pilots experienced at least a periodofvoluntary(26.8 ± 8.0 min, n = 4)orinvoluntarysleep (N1 sleep stage, 26.6 ± 18.7 s, n = 7) during the flight. Automatic classification (wake/sleep) by the algorithm was made for 10-s epochs (O1-M2 or C3-M2 channel), based on comparison of means to detect changes in α, β, and θ relative power, or ratio [(α + θ)/β], or fuzzy logic fusion (α, β). Pertinence and prognostic of the algorithm were determined using epoch-by-epoch comparison with visual-scoring (two blinded readers, AASM rules). The best concordance between automatic detection and visualscoring was observed within the O1-M2 channel, using the ratio [(α + θ)/β] (98.3 ± 4.1% of good detection, K = 0.94 ± 0.07, with a 0.04 ± 0.04 false positive rate and a 0.87 ± 0.10 true positive rate). Our results confirm the efficiency of a miniaturized single electroencephalographic channel recording device, associated with an automatic detection algorithm, in order to detect low-vigilance states during real flights.

Napping Reverses the Salivary Interleukin-6 and Urinary Norepinephrine Changes Induced by Sleep Restriction

CONTEXT Neuroendocrine and immune stresses imposed by chronic sleep restriction are known to be involved in the harmful cardiovascular effects associated with poor sleep. OBJECTIVES Despite a well-known beneficial effect of napping on alertness, its effects on neuroendocrine stress and immune responses after sleep restriction are largely unknown. DESIGN This study was a strictly controlled (sleep-wake status, light environment, caloric intake), crossover, randomized design in continuously polysomnography-monitored subjects. SETTING The study was conducted in a laboratory-based study. PARTICIPANTS The subjects were 11 healthy young men. INTERVENTION We investigated the effects on neuroendocrine and immune biomarkers of a night of sleep restricted to 2 h followed by a day without naps or with 30 minute morning and afternoon naps, both conditions followed by an ad libitum recovery night starting at 20:00. MAIN OUTCOME MEASURES Salivary interleukin-6 and urinary catecholamines were assessed throughout the daytime study periods. RESULTS The increase in norepinephrine values seen at the end of the afternoon after the sleep-restricted night was not present when the subjects had the opportunity to take naps. Interleukin-6 changes observed after sleep deprivation were also normalized after napping. During the recovery day in the no-nap condition, there were increased levels of afternoon epinephrine and dopamine, which was not the case in the nap condition. A recovery night after napping was associated with a reduced amount of slow-wave sleep compared to after the no-nap condition. CONCLUSIONS Our data suggest that napping has stress-releasing and immune effects. Napping could be easily applied in real settings as a countermeasure to the detrimental health consequences of sleep debt.

Effects of acute and chronic sleep deprivation on daytime alertness and cognitive performance of healthy snorers and non-snorers

BACKGROUND Respiratory events during sleep usually lead to micro arousals resulting in consecutive daytime sleepiness even in healthy snorers. The present study investigated the evolution of subjective and objective daytime sleepiness and reaction time in healthy snorers submitted to acute and chronic sleep deprivation. METHODS Objective sleepiness was measured by the MSLT, subjective sleepiness by the Karolinska Sleepiness Scale (KSS), and reaction time (RT) by the Psychomotor Vigilance Test. Mean sleep latencies, KSS scores and performance were analyzed through repeated measures ANOVAs with one between-factor (snorers and non-snorers) and two within-factors (sleep deprivation [baseline, acute, and chronic sleep deprivation] and time-of-day). RESULTS The findings reveal that sleep deprivation does not enhance snoring but that, during baseline, objective daytime sleepiness is higher in snorers than in non-snorers (shorter sleep latencies) with no difference in subjective assessments. The effects of acute and chronic sleep deprivation on sleep are similar in both groups, but, after acute sleep deprivation, RT and attentional lapses (RT >500 ms) are higher in snorers. Chronic sleep deprivation produces similar results in both groups. CONCLUSION These results suggest that respiratory efforts may be involved in the increased vulnerability to sleep deprivation of healthy snorers when compared to non-snorers.

Association between insomnia symptoms, job strain and burnout syndrome: a cross-sectional survey of 1300 financial workers

Objectives Professional burnout is closely related to work stress but less frequently associated with disturbed sleep. This study determines whether job strain and sleep disturbances are associated risk factors of burnout among financial workers. Design Observational study. Participants 1300 employees (725 female) of a financial company. Primary measures Self-reported questionnaires (Maslach Burnout Inventory, Job Content Questionnaire, Sleep questionnaire based on ICSD-3 classification), the Epworth sleepiness scale and the Hospital Anxiety and Depression Scale (HADS). Result The prevalence of burnout was 10.2% (9.0% moderate and 1.2% severe). 23.3% of workers were considered with high job strain, and 93.1% had a high level of job satisfaction. 16.8% of individuals had insomnia and 97% reported non-restorative sleep. The bivariate analyses demonstrate a higher risk of burnout in participants with insomnia (OR=14.7, 95% CI 9.8 to 21.9), non-restorative sleep (OR=9.9, 95% CI 5.1 to 19.5) and anxiety (OR=10.2, 95% CI 6.8 to 15.3). High job strain was associated with burnout (OR=1.9, 95% CI 1.1 to 3.6). This association was not maintained after adjustment for sleep parameters. Job satisfaction was another independent risk factor for burnout (OR=124, 95% CI 65 to 237). Conclusions In our sample of financial workers, job strain represents a burnout risk factor only if associated with insomnia. Insomnia can be considered as a relevant clinical marker that should be targeted in mental health prevention programmes at the workplace.

Using actigraphy versus polysomnography in the clinical assessment of chronic insomnia (retrospective analysis of 27 patients)

AIM The current study was conducted in order to investigate whether several different methods of characterizing sleep and insomnia symptoms produce different diagnoses. METHOD To this aim, we performed a retrospective study in order to compare the outcome of the assessment obtained using actigraphy with that obtained using polysomnography (PSG) in 27 outpatients complaining of chronic insomnia. Subjects were recruited from a database consisting of patients referred to the sleep centre of the Hôtel-Dieu Hospital (Paris) complaining of chronic insomnia. Patients were divided into different groups with regard to type of insomnia. RESULTS As far as type of insomnia was concerned, the comparison between actigraphy and PSG showed quite a good contingency coefficient value (C=0.64). CONCLUSION Although this was a preliminary and retrospective study, our results seemed to indicate that actigraphy and PSG were able to lead to a similar output particularly with regard to type of insomnia. Beyond PSG, actigraphy might have a clinical utility in assessing sleep disorders in adults complaining of chronic insomnia.

Alzheimer's Disease Severity is Not Significantly Associated with Short Sleep: Survey by Actigraphy on 208 Mild and Moderate Alzheimer's Disease Patients.

BACKGROUND In epidemiological surveys, cognitive decline has been found to be associated with both short and long sleep duration. OBJECTIVE Our goal was to objectively determine how total sleep time (TST) at night was associated or not with apathy or severity scores in patients with Alzheimer s disease (AD). METHODS During an observational first step of a clinical trial, sleep was assessed in institutionalized patients with mild or moderate AD using actigraphy (MW8, Camtech, Cambridge, UK) for 14 consecutive 24-hour periods. Sleep parameters analyzed were: TST, time in bed (TIB), wake after sleep onset (WASO), sleep efficiency (SE) defined by the ratio TST/TIB, in percentage), the number and length of awakenings, the night fragmentation index, the interdaily stability, and intradaily variability indexes. Statistical association analyses were tested between these values and AD apathy and severity scores. RESULTS 208 individuals coming from 82 centers worldwide (France, Germany, Spain, Italy, Portugal, Poland, United States, Canada, and Australia) and≥50 years old participated. Their average TST was 7 hours and 35 minutes and the average WASO 58 minutes. TST and SE were significantly higher in patients with apathy and the number of awakenings was significantly lower. TST was also positively associated with functional disability (ADCS-ADL scores), but it was not found significantly greater in patients with a moderate AD severity compared to the mild. CONCLUSION Despite several and long awakenings, TST was not shorter in patients with AD. TST was even significantly increased with disability and apathy.

ActiWave : nouvelle technologie d’enregistrement du sommeil Test et faisabilité

Resume Dix sujets ont beneficie d’un enregistrement polygraphique ambulatoire de sommeil par la nouvelle technologie ActiWave. Tous les resultats des dix patients ont ete telecharges avec succes. Les signaux EEG/EOG et EMG sont d’une qualite acceptable. La legerete et l’ergonomie de l’appareillage permettent au patient de dormir d’une maniere confortable. Des etudes complementaires, comparant cette nouvelle technologie aux mesures standard de reference, sont necessaires afin de valider l’utilisation de ce materiel.

Sleep and biological parameters in professional burnout: A psychophysiological characterization

Professional burnout syndrome has been described in association with insomnia and metabolic, inflammatory and immune correlates. We investigated the interest of exploring biological parameters and sleep disturbances in relation to burnout symptoms among white-collar workers. Fifty-four participants with burnout were compared to 86 healthy control participants in terms of professional rank level, sleep, job strain (Karasek questionnaire), social support, anxiety and depression (HAD scale). Fasting concentrations of glycaemia, glycosylated hemoglobin (HbA1C), total-cholesterol, triglycerides, C-reactive protein (CRP), thyroid stimulating hormone (TSH), 25-hydroxyvitamin D (25[OH]D), and white blood cell (WBC) counts were assessed. Analysis of variance and a forward Stepwise Multiple Logistic Regression were made to identify predictive factors of burnout. Besides reporting more job strain (in particular job control p = 0.02), higher levels of anxiety (p<0.001), and sleep disorders related to insomnia (OR = 21.5, 95%CI = 8.8–52.3), participants with burnout presented higher levels of HbA1C, glycaemia, CRP, lower levels of 25(OH)D, higher number of leukocytes, neutrophils and monocytes (P<0.001 for all) and higher total-cholesterol (P = 0.01). In particular, when HbA1c is > 3.5%, the prevalence of burnout increases from 16.6% to 60.0% (OR = 4.3, 95%CI = 2.8–6.9). Strong significant positive correlation existed between HbA1C and the two dimensions (emotional exhaustion and depersonalization (r = 0.79 and r = 0.71, p<0.01)) of burnout. Models including job strain, job satisfaction, anxiety and insomnia did not predict burnout (p = 0.30 and p = 0.50). However, when HbA1C levels is included, the prediction of burnout became significant (P = 0.03). Our findings demonstrated the interest of sleep and biological parameters, in particular HbA1C levels, in the characterization of professional burnout.

Évaluation d’un nouvel Actigraphe MotionWatch8 en comparaison à la Polysomnographie sur 20 bons dormeurs et 50 patients suspectés d’avoir des troubles du sommeil

Le Karolinska Drowsiness Test (KDT) est une méthode itérative d’évaluation objective de la somnolence. Ce test repose sur le calcul de la puissance spectrale dans la bande de fréquence alphatheta de l’électroencéphalogramme (EEG) purifié. La réjection visuelle d’artefacts (mouvements, clignements) est réalisée par un expert de l’EEG de veille. Cette procédure, longue et fastidieuse, est un obstacle à l’utilisation de ce test. L’objet de l’étude est la mise au point d’un algorithme automatique de réjection d’artefact de l’EEG de veille. Vingt-cinq volontaires (20—75 ans) ont participé à cette étude incluant deux protocoles de 40 h de constant routine, comprenant chacun 11 KDT de quatre minutes, réalisés toutes les 3h45. L’analyse visuelle repose sur les signaux EEG Fz, Cz, Oz référencés à A2, ainsi que sur les signaux EOG, EMG et ECG. L’algorithme automatique, qui utilise uniquement le signal Fz, a été mis au point sur les KDT de trois sujets, soit 66 tests. Il a ensuite été évalué sur 20 autres KDT venant de 20 sujets. La réjection d’artefact a été réalisée automatiquement (A) et manuellement à deux reprises espacées d’un mois (M1 et M2l) La puissance spectrale du signal Fz dans la bande 6—9 Hz est calculée par époques de quatre secondes d’EEG purifié, puis moyennée pour arriver à une valeur par test. Ce calcul est réalisé sur chaque EEG purifié par A, M1, M2. La comparaison des méthodes porte sur le nombre d’époques rejetées et le résultat du test qui en découle. Les pourcentages moyens d’époques rejetées sont de 33 % (A), 45 % (M1), et 44 % (M2). L’ANOVA sur les résultats des tests n’a montré aucun effet scoreur. En conclusion, il n’y a pas de différence significative entre les valeurs de puissance theta-alpha selon que le type de purification des signaux EEG a été réalisé par l’algorithme ou par l’expert. Bien que l’analyse automatique rejette une plus faible quantité d’époques, elle fournit un résultat d’analyse spectrale comparable à celui de l’expert avec un gain significatif de temps. Ce résultat suggère que l’information contenue dans une seule dérivation EEG est suffisante réaliser un test KDT.