Experimental Night Research Articles

P173 Bi-frontal transcranial direct current stimulation does modulate sleep, but does not affect sleep-related memory consolidation

The crucial role of a hippocampal-cortical replay that gradually strengthens hippocampus-independent cortico-cortical connections has been recently emphasized for the prefrontal cortex (PFC). In a prior analysis, we demonstrated that bi-frontal anodal tDCS significantly decreased total sleep time in healthy participants. To further elucidate the relevance of prefrontal activity levels for sleep-related memory consolidation, we explore the effects of bi-frontal tDCS on pre-post sleep memory consolidation. 18 healthy participants (13 females, age 53.1 ± 6.6 years) underwent three experimental nights with one of three counterbalanced tDCS protocols (anodal, cathodal, sham) immediately prior to polysomnography (11 pm to 7 am, interval of 3–7 d). tDCS was transferred via two pairs of electrodes (5 × 7 cm over FP1/FP2 and 10 cm x 10 cm over P3/P4) covered with electrode cream (1 mA over each target electrode, ramp up/down of 30 s, interstimulus interval 20 min). At 8 pm, 46 semantically related word-pairs were presented in a randomized order (Presentation® software) followed by repeatedly tapping a five-element sequence of numbers as fast and accurately as possible. At 8 am on the following morning, memory retrieval was assessed in a cued recall test for word-pairs (percentage of correctly retrieved referred to encoded words) and in a finger tapping test session (percentage of average speed and accuracy improvement). Bi-frontal tDCS did not result in significant changes in pre-post sleep memory consolidation in either of the examined memory systems. Specifically, repeated measures analyses of variance detected no significant condition effect for the percentage of correct word pairs ( F = 0.2, p = 0.820, pETA 2 = 0.012), finger tapping speed ( F = 1.9, p = 0.167, pETA 2 = 0.113) or accuracy ( F = 0.1, p = 0.827, pETA 2 = 0.010). In contrast to our finding of a decreased total sleep time in healthy participants following bi-frontal anodal tDCS, the stimulation protocol did not influence sleep-related memory consolidation. As mainly remote memory has been proposed to be dependent on the PFC, the test interval could have been too short to detect long-term memory effects. Besides, the results support that sleep modulating tDCS can be considered a safe and promising tool without severe adverse cognitive effects.

Experimental illumination of a forest: no effects of lights of different colours on the onset of the dawn chorus in songbirds.

Light pollution is increasing exponentially, but its impact on animal behaviour is still poorly understood. For songbirds, the most repeatable finding is that artificial night lighting leads to an earlier daily onset of dawn singing. Most of these studies are, however, correlational and cannot entirely dissociate effects of light pollution from other effects of urbanization. In addition, there are no studies in which the effects of different light colours on singing have been tested. Here, we investigated whether the timing of dawn singing in wild songbirds is influenced by artificial light using an experimental set-up with conventional street lights. We illuminated eight previously dark forest edges with white, green, red or no light, and recorded daily onset of dawn singing during the breeding season. Based on earlier work, we predicted that onset of singing would be earlier in the lighted treatments, with the strongest effects in the early-singing species. However, we found no significant effect of the experimental night lighting (of any colour) in the 14 species for which we obtained sufficient data. Confounding effects of urbanization in previous studies may explain these results, but we also suggest that the experimental night lighting may not have been strong enough to have an effect on singing.

Slow wave and REM sleep deprivation effects on explicit and implicit memory during sleep.

It has been debated whether different stages in the human sleep cycle preferentially mediate the consolidation of explicit and implicit memories, or whether all of the stages in succession are necessary for optimal consolidation. Here we investigated whether the selective deprivation of slow wave sleep (SWS) or rapid eye movement (REM) sleep over an entire night would have a specific effect on consolidation in explicit and implicit memory tasks. Participants completed a set of explicit and implicit memory tasks at night, prior to sleep. They had 1 control night of undisturbed sleep and 2 experimental nights, during which either SWS or REM sleep was selectively deprived across the entire night (sleep conditions counterbalanced across participants). Polysomnography recordings quantified precisely the amount of SWS and REM sleep that occurred during each of the sleep conditions, and spindle counts were recorded. In the morning, participants completed the experimental tasks in the same sequence as the night before. SWS deprivation disrupted the consolidation of explicit memories for visuospatial information (ηp2 = .23), and both SWS (ηp2 = .53) and REM sleep (ηp2 = .52) deprivation adversely affected explicit verbal recall. Neither SWS nor REM sleep deprivation affected aspects of short-term or working memory, and did not affect measures of verbal implicit memory. Spindle counts did not correlate significantly with memory performance. These findings demonstrate the importance of measuring the sleep cycles throughout the entire night, and the contribution of both SWS and REM sleep to memory consolidation. (PsycINFO Database Record

EPV 10. Bi-frontal transcranial direct current stimulation does not modulate sleep continuity in patients with insomnia

Objective and background The most influential neurobiological model of insomnia disorder is the ‘hyperaorusal model’, which states increased level of arousal during day and nighttime as a fundamental characteristic of the disorder ( Riemann et al., 2010 ). Prior work emphasizes the crucial role of cortical activity levels and cortico-thalamic feedback in this disorder ( Nofzinger et al., 2004 ). In a prior study, our research group demonstrated that bi-frontal anodal tDCS significantly decreased total sleep time (TST) and increased cortical arousal during wakefulness as indexed by resting state EEG gamma power in healthy participants ( Frase et al., 0000 ). To further elucidate the relevance of prefrontal activity levels in insomnia disorder, we tested the hypothesis that bi-frontal cathodal tDCS results in an increase of TST by reducing cortical hyperarpousal in patients with insomnia with anodal tDCS inducing reverse effects. Methods Nineteen patients with nonorganic insomnia (13 females, 6 males, age 43.8 ± 15.1 years, 20–60 years) were included in the analysis. After adaptation to the sleep laboratory conditions, each participant underwent a baseline and three experimental nights in intervals of 3–7 days with a tDCS protocol immediately prior to polysomnography (11 pm to 7 am) according to standard procedures. The polysomnographic parameter total sleep time (TST) was defined as the main outcome parameter for of sleep continuity. Three different conditions (activation, deactivation, sham) were applied in a counterbalanced order. tDCS was delivered by a battery-driven, micro-processor-controlled constant current stimulator (Neuro-conn, Illmenau, Germany) and transferred by two pairs of electrodes (5 cm × 7 cm and 10 cm × 10 cm) covered with electrode cream positioned over FP1/FP2, respectively over P3/P4. A current of 1 mA was applied over each target electrode with a ramp up/ramp down of 30 s at the start and end of each stimulation and an interstimulusinterval (ISI) of 20 min. Results In contrast to our hypothesis, bi-frontal tDCS did not result in significant changes in sleep continuity or architecture. Analyses of subjective sleep ratings detected no differences between conditions (Repeated measures ANOVAs conducted for all three conditions separately, all p > 0.6). Discussion In contrast to our findings in healthy participants, the current results in patients with insomnia do not show differences in sleep continuity after tDCS. Instead, the sleep pattern in insomnia patients appears to be robust to cortical stimulation, which could be caused by persistant hyperarousal overriding possible tDCS-effects.

Behavioural plasticity in the onset of dawn song under intermittent experimental night lighting

The disruption of daily rhythms is one of the most studied ecological consequences of light pollution. Previous work showed that several songbird species initiated dawn song earlier in areas with light pollution. However, the mechanisms underlying this shift are still unknown. Individuals may immediately adjust their timing of singing to the presence of artificial light (behavioural plasticity), but the observed effect may also be due to phenotype-dependent habitat choice, effects of conditions during early life or micro-evolution. The main aim of this study was to experimentally investigate how males of four common passerine species respond to day-to-day variation in the presence of artificial night lighting in terms of the timing of singing. During two consecutive breeding seasons, we manipulated the presence of light throughout the night in a cyclic fashion in several naturally undisturbed forest patches. We show that individuals of all four species immediately and reversibly adjusted their onset of dawn singing in response to artificial light. The effect was strongest in the European robin, but relatively small in the blue tit, the great tit and the blackbird. The effect in the latter two species was smaller than expected from the correlational studies. This may be coincidence (small sample size of this study), but it could also indicate that there are longer-term effects of living in light-polluted urban areas on timing of dawn singing, or that birds use compensatory behaviours such as light avoidance. We found no evidence that our light treatment had carryover effects into the subsequent dark period, but robins progressively advanced their dawn singing during the light treatment.

Modulation of Total Sleep Time by Transcranial Direct Current Stimulation (tDCS).

Arousal and sleep are fundamental physiological processes, and their modulation is of high clinical significance. This study tested the hypothesis that total sleep time (TST) in humans can be modulated by the non-invasive brain stimulation technique transcranial direct current stimulation (tDCS) targeting a 'top-down' cortico-thalamic pathway of sleep-wake regulation. Nineteen healthy participants underwent a within-subject, repeated-measures protocol across five nights in the sleep laboratory with polysomnographic monitoring (adaptation, baseline, three experimental nights). tDCS was delivered via bi-frontal target electrodes and bi-parietal return electrodes before sleep (anodal 'activation', cathodal 'deactivation', and sham stimulation). Bi-frontal anodal stimulation significantly decreased TST, compared with cathodal and sham stimulation. This effect was location specific. Bi-frontal cathodal stimulation did not significantly increase TST, potentially due to ceiling effects in good sleepers. Exploratory resting-state EEG analyses before and after the tDCS protocols were consistent with the notion of increased cortical arousal after anodal stimulation and decreased cortical arousal after cathodal stimulation. The study provides proof-of-concept that TST can be decreased by non-invasive bi-frontal anodal tDCS in healthy humans. Further elucidating the 'top-down' pathway of sleep-wake regulation is expected to increase knowledge on the fundamentals of sleep-wake regulation and to contribute to the development of novel treatments for clinical conditions of disturbed arousal and sleep.

Artificial light on water attracts turtle hatchlings during their near shore transit.

We examined the effect of artificial light on the near shore trajectories of turtle hatchlings dispersing from natal beaches. Green turtle (Chelonia mydas) hatchlings were tagged with miniature acoustic transmitters and their movements tracked within an underwater array of 36 acoustic receivers placed in the near shore zone. A total of 40 hatchlings were tracked, 20 of which were subjected to artificial light during their transit of the array. At the same time, we measured current speed and direction, which were highly variable within and between experimental nights and treatments. Artificial lighting affected hatchling behaviour, with 88% of individual trajectories oriented towards the light and spending, on average, 23% more time in the 2.25 ha tracking array (19.5 ± 5 min) than under ambient light conditions (15.8 ± 5 min). Current speed had little to no effect on the bearing (angular direction) of the hatchling tracks when artificial light was present, but under ambient conditions it influenced the bearing of the tracks when current direction was offshore and above speeds of approximately 32.5 cm s−1. This is the first experimental evidence that wild turtle hatchlings are attracted to artificial light after entering the ocean, a behaviour that is likely to subject them to greater risk of predation. The experimental protocol described in this study can be used to assess the effect of anthropogenic (light pollution, noise, etc.) and natural (wave action, current, wind, moonlight) influences on the in-water movements of sea turtle hatchlings during the early phase of dispersal.

Learning and sleep-dependent consolidation of spatial and procedural memories are unaltered in young men under a fixed short sleep schedule

ObjectiveTo investigate if a fixed short sleep schedule impairs one of the main functions of sleep, which is to consolidate newly learned memories. MethodsSixteen young men participated in two experimental conditions, each of which lasted for 3 consecutive days and nights in our laboratory: a short sleep schedule (4.25-h sleep opportunity per night) versus a normal sleep schedule (8.5h per night). In the evening after two experimental nights, participants learned locations of 15 card pairs (spatial memory task) and a procedural finger tapping sequence task. Post-sleep retrieval of both memory tasks was tested the next morning. ResultsThe short sleep schedule, compared with the normal sleep schedule, considerably altered sleep characteristics, e.g. the proportion of time in slow-wave sleep increased across the three experimental nights. In contrast, neither learning in the evening of day 2, nor subsequent overnight memory consolidation (i.e. concerning the change in memory performance between pre-sleep learning on day 2 and post-sleep retrieval on day 3) differed between the normal and short sleep schedule conditions. ConclusionsOur findings suggest that learning in the evening and subsequent sleep-dependent consolidation of procedural and spatial memories are unaltered in young men living under a fixed short sleep schedule. Future studies are warranted to validate our findings in other groups (e.g. adolescents and older subjects) and after more prolonged chronic sleep loss paradigms.

A 30-Minute, but Not a 10-Minute Nighttime Nap is Associated with Sleep Inertia.

To assess sleep inertia following 10-min and 30-min naps during a simulated night shift. Thirty-one healthy adults (aged 21-35 y; 18 females) participated in a 3-day laboratory study that included one baseline (BL) sleep (22:00-07:00) and one experimental night involving randomization to either: total sleep deprivation (NO-NAP), a 10-min nap (10-NAP) or a 30-min nap (30-NAP). Nap opportunities ended at 04:00. A 3-min psychomotor vigilance task (PVT-B), digit-symbol substitution task (DSST), fatigue scale, sleepiness scale, and self-rated performance scale were undertaken pre-nap (03:00) and at 2, 17, 32, and 47 min post-nap. The 30-NAP (14.7 ± 5.7 min) had more slow wave sleep than the 10-NAP (0.8 ± 1.5 min; P < 0.001) condition. In the NO-NAP condition, PVT-B performance was worse than pre-nap (4.6 ± 0.3 1/sec) at 47 min post-nap (4.1 ± 0.4 1/sec; P < 0.001). There was no change across time in the 10-NAP condition. In the 30-NAP condition, performance immediately deteriorated from pre-nap (4.3 ± 0.3 1/sec) and was still worse at 47 min post-nap (4.0 ± 0.5 1/sec; P < 0.015). DSST performance deteriorated in the NO-NAP (worse than pre-nap from 17 to 47 min; P < 0.008), did not change in the 10-NAP, and was impaired 2 min post-nap in the 30-NAP condition (P = 0.028). All conditions self-rated performance as better than pre-nap for all post-nap test points (P < 0.001). This study is the first to show that a 10-min (but not a 30-min) nighttime nap had minimal sleep inertia and helped to mitigate short-term performance impairment during a simulated night shift. Self-rated performance did not reflect objective performance following a nap.

Effect of conditioned stimulus exposure during slow-wave sleep on fear memory extinction in humans

STUDY OBJECTIVES Repeated exposure to a neutral conditioned stimulus (CS) in the absence of a noxious unconditioned stimulus (US) elicits fear memory extinction. The aim of the current study was to investigate the effects of mild tone exposure (CS) during slow wave sleep (SWS) on fear memory extinction in humans. DESIGN The healthy volunteers underwent an auditory fear conditioning paradigm on the experimental night, during which tones served as the CS, and a mild shock served as the US. They were then randomly assigned to four groups. Three groups were exposed to the CS for 3 or 10 min or an irrelevant tone (control stimulus, CtrS) for 10 min during SWS. The fourth group served as controls and was not subjected to any interventions. All of the subjects completed a memory test 4 h after SWS-rich stage to evaluate the effect on fear extinction. Moreover, we conducted similar experiments using an independent group of subjects during the daytime to test whether the memory extinction effect was specific to the sleep condition. PARTICIPANTS Ninety-six healthy volunteers (44 males) aged 18-28 y. MEASUREMENTS AND RESULTS Participants exhibited undisturbed sleep during 2 consecutive nights, as assessed by sleep variables (all P > 0.05) from polysomnographic recordings and power spectral analysis. Participants who were re-exposed to the 10 min CS either during SWS and wakefulness exhibited attenuated fear responses (wake-10 min CS, P < 0.05; SWS-10 min CS, P < 0.01). CONCLUSIONS Conditioned stimulus re-exposure during SWS promoted fear memory extinction without altering sleep profiles.

Diurnal Emotional States Impact the Sleep Course.

BackgroundDiurnal emotional experiences seem to affect several characteristics of sleep architecture. However, this influence remains unclear, especially for positive emotions. In addition, electrodermal activity (EDA), a sympathetic robust indicator of emotional arousal, differs depending on the sleep stage. The present research has a double aim: to identify the specific effects of pre-sleep emotional states on the architecture of the subsequent sleep period; to relate such states to the sympathetic activation during the same sleep period.MethodsTwelve healthy volunteers (20.1 ± 1.0 yo.) participated in the experiment and each one slept 9 nights at the laboratory, divided into 3 sessions, one per week. Each session was organized over three nights. A reference night, allowing baseline pre-sleep and sleep recordings, preceded an experimental night before which participants watched a negative, neutral, or positive movie. The third and last night was devoted to analyzing the potential recovery or persistence of emotional effects induced before the experimental night. Standard polysomnography and EDA were recorded during all the nights.ResultsFirstly, we found that experimental pre-sleep emotional induction increased the Rapid Eye Movement (REM) sleep rate following both negative and positive movies. While this increase was spread over the whole night for positive induction, it was limited to the second half of the sleep period for negative induction. Secondly, the valence of the pre-sleep movie also impacted the sympathetic activation during Non-REM stage 3 sleep, which increased after negative induction and decreased after positive induction.ConclusionPre-sleep controlled emotional states impacted the subsequent REM sleep rate and modulated the sympathetic activity during the sleep period. The outcomes of this study offer interesting perspectives related to the effect of diurnal emotional influences on sleep regulation and open new avenues for potential practices designed to alleviate sleep disturbances.

Sophisticated evaluation of possible effect of distinct auditory stimulation during REM sleep on dream content

Introducti o n : Studies have revealed significant impacts of different external stimuli during sleep on dream content and have reported various incorporation rates. The present study was performed to evaluate possible effect of auditory stimulation with sophisticated method. Materials and Methods: For this purpose, fifteen healthy male volunteers, who were tested for having normal auditory sensation, slept for two consecutive nights on sleep laboratory and monitored by polysomnography device. Subjects were not informed about content and time in which the sound was played. Traffic ambience sound (40‐60 decibel for 1 minute) played during second Rapid eye movement (REM) sleep of experimental (second) night and self-written dream report has collected after second and fourth REM sleep of both nights. Dream reports were coded by two independent coders according the Hall and de castle coding rules. Results: Dreaming something related to traffic sound (according to coding rules) was reported significantly more in dream reports of second REM of experimental night (in which sound was played) in comparison to dream reports of second REM of control night(p=0.033). Direct incorporation of traffic sound was reported in 78% subjects. Conclusion: Our finding revealed that information processing of auditory stimuli continues during sleep and can affect dream content, much more than previously estimated. The evaluation of possible correlated EEG changes when dream has been affected by external auditory stimuli is needed in future studies.

The Impact of Nocturnal Hypoglycemia on Sleep in Subjects With Type 2 Diabetes.

The aim of this trial was to investigate the impact of nocturnal hypoglycemia on sleep patterns (assessed by polysomnography) and counterregulatory hormones. In this single-blinded, crossover trial, 26 subjects with type 2 diabetes attended two experimental night visits (one normoglycemic and one hypoglycemic) in randomized order. Plasma glucose (PG) levels were controlled by hyperinsulinemic glucose clamping. On the hypoglycemic night, hypoglycemia was induced after reaching sleep stage N2 by turning off glucose infusion until the PG target of 2.7-2.8 mmol/L was reached and maintained for 15 min. Thereafter, subjects were brought back to normoglycemia for the rest of the night. On the normoglycemic night, PG was maintained at 5.0-7.0 mmol/L throughout the night. During the first 4 h of sleep (0-4 h; after reaching sleep stage N2), no difference between experimental nights was observed in the rate of electroencephalography-identified arousals or awakenings, but the rate of awakenings was 27% lower during 4-8 h and 20% lower during 0-8 h on the hypoglycemic night than on the normoglycemic night (both statistically significant). Total sleep time tended to be longer on the hypoglycemic night (observed means 366 vs. 349 min, P nonsignificant). Statistically significantly higher counterregulatory hormonal responses (adrenaline, growth hormone, and cortisol) to hypoglycemia were observed compared with normoglycemia. Nocturnal hypoglycemia in patients with type 2 diabetes caused a decrease in awakening response in the 4-8-h period following the event. These findings underscore the risks associated with nocturnal hypoglycemia because nocturnal hypoglycemia potentially affects the patient's ability to wake up and respond with an adequate intake of carbohydrates.

Slow oscillating transcranial direct current stimulation during non-rapid eye movement sleep improves behavioral inhibition in attention-deficit/hyperactivity disorder.

Background: Behavioral inhibition, which is a later-developing executive function (EF) and anatomically located in prefrontal areas, is impaired in attention-deficit and hyperactivity disorder (ADHD). While optimal EFs have been shown to depend on efficient sleep in healthy subjects, the impact of sleep problems, frequently reported in ADHD, remains elusive. Findings of macroscopic sleep changes in ADHD are inconsistent, but there is emerging evidence for distinct microscopic changes with a focus on prefrontal cortical regions and non-rapid eye movement (non-REM) slow-wave sleep. Recently, slow oscillations (SO) during non-REM sleep were found to be less functional and, as such, may be involved in sleep-dependent memory impairments in ADHD.Objective:By augmenting slow-wave power through bilateral, slow oscillating transcranial direct current stimulation (so-tDCS, frequency = 0.75 Hz) during non-REM sleep, we aimed to improve daytime behavioral inhibition in children with ADHD.Methods: Fourteen boys (10–14 years) diagnosed with ADHD were included. In a randomized, double-blind, cross-over design, patients received so-tDCS either in the first or in the second experimental sleep night. Inhibition control was assessed with a visuomotor go/no-go task. Intrinsic alertness was assessed with a simple stimulus response task. To control for visuomotor performance, motor memory was assessed with a finger sequence tapping task.Results: SO-power was enhanced during early non-REM sleep, accompanied by slowed reaction times and decreased standard deviations of reaction times, in the go/no-go task after so-tDCS. In contrast, intrinsic alertness, and motor memory performance were not improved by so-tDCS.Conclusion: Since behavioral inhibition but not intrinsic alertness or motor memory was improved by so-tDCS, our results suggest that lateral prefrontal slow oscillations during sleep might play a specific role for executive functioning in ADHD.

Analysing chemical attraction of gravid Anopheles gambiae sensu stricto with modified BG-Sentinel traps.

BackgroundCues that guide gravid Anopheles gambiae sensu lato to oviposition sites can be manipulated to create new strategies for monitoring and controlling malaria vectors. However, progress towards identifying such cues is slow in part due to the lack of appropriate tools for investigating long-range attraction to putative oviposition substrates. This study aimed to develop a relatively easy-to-use bioassay system that can effectively analyse chemical attraction of gravid Anopheles gambiae sensu stricto.MethodsBG-Sentinel™ mosquito traps that use fans to dispense odourants were modified to contain aqueous substrates. Choice tests with two identical traps set in an 80 m2 screened semi-field system were used to analyse the catch efficacy of the traps and the effectiveness of the bioassay. A different batch of 200 gravid An. gambiae s.s. was released on every experimental night. Choices tested were (1) distilled versus distilled water (baseline) and (2) distilled water versus soil infusion. Further, comparisons were made of distilled water and soil infusions both containing 150 g/l of Sodium Chloride (NaCl). Sodium Chloride is known to affect the release rate of volatiles from organic substrates.ResultsWhen both traps contained distilled water, 45 % (95 confidence interval (CI) 33–57 %) of all released mosquitoes were trapped. The proportion increased to 84 % (95 CI 73–91 %) when traps contained soil infusions. In choice tests, a gravid female was twice as likely to be trapped in the test trap with soil infusion as in the trap with distilled water (odds ratio (OR) 1.8, 95 % CI 1.3–2.6). Furthermore, the attraction of gravid females towards the test trap with infusion more than tripled (OR 3.4, 95 % CI 2.4–4.8) when salt was added to the substrates.ConclusionMinor modifications of the BG-Sentinel™ mosquito trap turned it into a powerful bioassay tool for evaluating the orientation of gravid mosquitoes to putative oviposition substrates using olfaction. This study describes a useful tool for investigating olfactory attraction of gravid An. gambiae s.s. and provides additional evidence that gravid mosquitoes of this species are attracted to and can be baited with attractive substrates such as organic infusions over a distance of several metres.

Role of sleep for encoding of emotional memory

Total sleep deprivation (TSD) has been consistently found to impair encoding of information during ensuing wakefulness, probably through suppressing NonREM (non-rapid eye movement) sleep. However, a possible contribution of missing REM sleep to this encoding impairment after TSD has so far not been systematically examined in humans, although such contribution might be suspected in particular for emotional information. Here, in two separate experiments in young healthy men, we compared effects of TSD and of selective REM sleep deprivation (REMD), relative to respective control conditions of undisturbed sleep, on the subsequent encoding of neutral and emotional pictures. The pictures were presented in conjunction with colored frames to also assess related source memory. REMD was achieved by tones presented contingently upon initial signs of REM sleep. Encoding capabilities were examined in the evening (18:00h) after the experimental nights, by a picture recognition test right after encoding. TSD significantly decreased both the rate of correctly recognized pictures and of recalled frames associated with the pictures. The TSD effect was robust and translated into an impaired long term memory formation, as it was likewise observed on a second recognition testing one week after the encoding phase. Contrary to our expectation, REMD did not affect encoding in general, or particularly of emotional pictures. Also, REMD did not affect valence ratings of the encoded pictures. However, like TSD, REMD distinctly impaired vigilance at the time of encoding. Altogether, these findings indicate an importance of NonREM rather than REM sleep for the encoding of information that is independent of the emotionality of the materials.

Effect of conditioned stimulus exposure during slow wave sleep on fear memory extinction in humans.

Repeated exposure to a neutral conditioned stimulus (CS) in the absence of a noxious unconditioned stimulus (US) elicits fear memory extinction. The aim of the current study was to investigate the effects of mild tone exposure (CS) during slow wave sleep (SWS) on fear memory extinction in humans. The healthy volunteers underwent an auditory fear conditioning paradigm on the experimental night, during which tones served as the CS, and a mild shock served as the US. They were then randomly assigned to four groups. Three groups were exposed to the CS for 3 or 10 min or an irrelevant tone (control stimulus, CtrS) for 10 min during SWS. The fourth group served as controls and was not subjected to any interventions. All of the subjects completed a memory test 4 h after SWS-rich stage to evaluate the effect on fear extinction. Moreover, we conducted similar experiments using an independent group of subjects during the daytime to test whether the memory extinction effect was specific to the sleep condition. Ninety-six healthy volunteers (44 males) aged 18-28 y. Participants exhibited undisturbed sleep during 2 consecutive nights, as assessed by sleep variables (all P > 0.05) from polysomnographic recordings and power spectral analysis. Participants who were re-exposed to the 10 min CS either during SWS and wakefulness exhibited attenuated fear responses (wake-10 min CS, P < 0.05; SWS-10 min CS, P < 0.01). Conditioned stimulus re-exposure during SWS promoted fear memory extinction without altering sleep profiles.

Sleep depth and continuity before and after chronic exercise in older men: Electrophysiological evidence

During later life sleep depth (slow-wave sleep, SWS) and maintenance exhibit deleterious changes, with possible negative effects on daytime function. This study assessed the effect of chronic, supervised exercise on sleep using laboratory-based polysomnography (PSG) and repeated measures in older adults. Thirteen men aged 64±3served as their own controls and had their sleep measured for a total of 6 nights: 3 before and 3 after the 16-week training intervention. Each sequence involved 1 familiarization trial followed by 2 experimental nights (exercise night; nonexercise night) measured using 13-channel PSG (combined electroencephalography, electromyography, and electro-oculography). The exercise challenges consisted of inclined treadmill brisk walking (60min, 68–69% V˙O2peak). The intervention successfully improved some parameters of aerobic fitness, i.e. ventilatory thresholds 1 and 2 (P<0.05). Acute exercise triggered increases in circulating free fatty acids and lactate levels both at baseline and after the intervention (P<0.05). Noteworthy, acute exercise following training resulted in a 71% increase in SWS during subsequent sleep in comparison with the nonexercise condition before training, respectively 2.4% and 1.4% (P<0.05). Following training, acute exercise reduced total wake time by 30% and REM onset latency by 14% (P<0.05). Acute exercise improved sleep continuity by decreasing total wake time. These results show that aerobic training could increase sleep depth and continuity, during active days, in elderly men. In habitual exercisers, these effects of aerobic exercise on sleep, although modest, might counteract those resulting from aging.

Cognitive workload and sleep restriction interact to influence sleep homeostatic responses.

Determine the effects of high versus moderate workload on sleep physiology and neurobehavioral measures, during sleep restriction (SR) and no sleep restriction (NSR) conditions. Ten-night experiment involving cognitive workload and SR manipulations. Controlled laboratory environment. Sixty-three healthy adults (mean ± standard deviation: 33.2 ± 8.7 y; 29 females), age 22-50 y. Following three baseline 8 h time in bed (TIB) nights, subjects were randomized to one of four conditions: high cognitive workload (HW) + SR; moderate cognitive workload (MW) + SR; HW + NSR; or MW + NSR. SR entailed 5 consecutive nights at 4 h TIB; NSR entailed 5 consecutive nights at 8 h TIB. Subjects received three workload test sessions/day consisting of 15-min preworkload assessments, followed by a 60-min (MW) or 120-min (HW) workload manipulation comprised of visually based cognitive tasks, and concluding with 15-min of postworkload assessments. Experimental nights were followed by two 8-h TIB recovery sleep nights. Polysomnography was collected on baseline night 3, experimental nights 1, 4, and 5, and recovery night 1 using three channels (central, frontal, occipital [C3, Fz, O2]). High workload, regardless of sleep duration, increased subjective fatigue and sleepiness (all P < 0.05). In contrast, sleep restriction produced cumulative increases in Psychomotor Vigilance Test (PVT) lapses, fatigue, and sleepiness and decreases in PVT response speed and Maintenance of Wakefulness Test (MWT) sleep onset latencies (all P < 0.05). High workload produced longer sleep onset latencies (P < 0.05, d = 0.63) and less wake after sleep onset (P < 0.05, d = 0.64) than moderate workload. Slow-wave energy-the putative marker of sleep homeostasis-was higher at O2 than C3 only in the HW + SR condition (P < 0.05). High cognitive workload delayed sleep onset, but it also promoted sleep homeostatic responses by increasing subjective fatigue and sleepiness, and producing a global sleep homeostatic response by reducing wake after sleep onset. When combined with sleep restriction, high workload increased local (occipital) sleep homeostasis, suggesting a use-dependent sleep response to visual work. We conclude that sleep restriction and cognitive workload interact to influence sleep homeostasis.

Slow sleep spindle activity, declarative memory, and general cognitive abilities in children.

Functional interactions between sleep spindle activity, declarative memory consolidation, and general cognitive abilities in school-aged children. Healthy, prepubertal children (n = 63; mean age 9.56 ± 0.76 y); ambulatory all-night polysomnography (2 nights); investigating the effect of prior learning (word pair association task; experimental night) versus nonlearning (baseline night) on sleep spindle activity; general cognitive abilities assessed using the Wechsler Intelligence Scale for Children-IV (WISC-IV). Analysis of spindle activity during nonrapid eye movement sleep (N2 and N3) evidenced predominant peaks in the slow (11-13 Hz) but not in the fast (13-15 Hz) sleep spindle frequency range (baseline and experimental night). Analyses were restricted to slow sleep spindles. Changes in spindle activity from the baseline to the experimental night were not associated with the overnight change in the number of recalled words reflecting declarative memory consolidation. Children with higher sleep spindle activity as measured at frontal, central, parietal, and occipital sites during both baseline and experimental nights exhibited higher general cognitive abilities (WISC-IV) and declarative learning efficiency (i.e., number of recalled words before and after sleep). Slow sleep spindles (11-13 Hz) in children age 8-11 y are associated with inter-individual differences in general cognitive abilities and learning efficiency.