Alain Hoeft

EEG spectral power and cognitive performance during sleep inertia: the effect of normal sleep duration and partial sleep deprivation.

Sleep inertia (SI) is a transient period occurring immediately after awakening, usually characterized by performance decrement. When sleep is sufficient, SI is moderate, and produces few or no deficit. When it is associated with prior sleep deprivation, SI shows dose-dependent negative effects on cognitive performance, especially when subjects have been awaken in slow wave sleep (SWS). In the present study, spectral analysis was applied during the last 10 min before and the first 10 min after awakening, and during 1 h after awakening while subjects performed the Stroop test. Seventeen subjects were divided into a Control group who slept 8 h, and a Sleep Deprived group who slept only 2 h. The results show that performance was normal in the Control group, whereas reaction time was increased during the first half hour and error level during the second half hour in the Sleep Deprived group. Spectral analysis applied on the waking EEG during the whole test session showed that alpha activity was increased in both groups, but theta power only in the Sleep Deprived group. There was a high positive correlation in sleep deprived subjects between delta power during the last 10 min of sleep and subsequent performance decrement in speed and accuracy. Comparison of individual records showed a high positive correlation between spectral power before and after awakening in the Control group (generally in the sense of an increased frequency band), but no correlation was found in the Sleep Deprived group who exhibited a rather disorganized pattern. We discuss these results in terms of incoherence in the EEG continuity during sleep offset after prior sleep loss, which could partly account for the performance decrement observed during SI in sleep deprived subjects.

Infants born very preterm react to variations of the acoustic environment in their incubator from a minimum signal-to-noise ratio threshold of 5 to 10 dBA

Introduction:Very early preterm infants (VPIs) are exposed to unpredictable noise in neonatal intensive care units. Their ability to perceive moderate acoustic environmental changes has not been fully investigated.Results:Physiological values of the 598 isolated sound peaks (SPs) that were 5–10 and 10–15 dB slow-response A (dBA) above background noise levels and that occured during infants’ sleep varied significantly, indicating that VPIs detect them. Exposure to 10–15 dBA SPs during active sleep significantly increased mean heart rate and decreased mean respiratory rate and mean systemic and cerebral oxygen saturations relative to baseline.Discussion:VPIs are sensitive to changes in their nosocomial acoustic environment, with a minimal signal-to-noise ratio (SNR) threshold of 5–10 dBA. These acoustic changes can alter their well-being.Methods:In this observational study, we evaluated their differential auditory sensitivity to sound-pressure level (SPL) increments below 70–75 dBA equivalent continuous level in their incubators. Environmental (SPL and audio recording), physiological, cerebral, and behavioral data were prospectively collected over 10 h in 26 VPIs (GA 28 (26–31) wk). SPs emerging from background noise levels were identified and newborns’ arousal states at the time of SPs were determined. Changes in parameters were compared over 5-s periods between baseline and the 40 s following the SPs depending on their SNR thresholds above background noise.

Impact of motivation on cognitive control in the context of vigilance lowering: an ERP study.

We assessed the effects of time-on-task on cognitive control expressed by the CRN/Nc and the extent to which motivation modulates this relationship. We utilized two groups of participants, who were told that their performance would (evaluation condition) or would not (control condition) be evaluated online. Both groups performed a version of the Eriksen Flanker Task for 60 min. We observed classical vigilance lowering, manifested by a progressive performance decline with time-on-task, in the control, but not in the evaluation, condition. In the latter, performance remained stable throughout the task. ERP analysis indicated the same interaction in our main component of interest, the CRN/Nc, whose amplitude decreased from the first to the last period in the control condition but remained stable over time in the evaluation condition. To our knowledge, this study is the first to demonstrate the impact of motivation on monitoring processes as indexed by the correct response negativity, in the context of a prolonged task. Vigilance lowering caused by a repetitive and prolonged flanker task, results in compromised response control and compromised control of correct responses. Our results suggest that alterations in ACC functioning may underlie vigilance decline and can be viewed as evidence that the action monitoring functions of the ACC can be positively affected by motivation.

INTERACTION OF AGE WITH TIME OF DAY AND MENTAL LOAD IN DIFFERENT COGNITIVE TASKS

Extensive research has demonstrated that shiftwork produces deleterious effects on health because of the desynchrony it induces in the biological clock. The problem is even more crucial for older workers who present, in addition, various decrements in their cognitive functioning, particularly on attention and memory. The present study assessed whether age was related to task complexity as a function of time of day and time-on-task in a rapid rotating work-rest schedule. 24 subjects (12 juniors: 20–30 years and 12 seniors: 50–60 years) performed either a simple task (visual discrimination) or a complex task (descending subtraction) on three different moments of the day simulating the main shifts (morning, evening, and night). Analysis indicated that an age effect was only present on the more complex task, which was demanding in attentional resources and memory load. Seniors had no deficit in performance on the simple task compared to juniors. The effect of time of day was restricted to the simple task for both age groups. However, some differential strategies appear to distinguish juniors and seniors, specifically on accuracy during the night, suggesting that subjects of different ages cope with cognitive tasks in different ways and that perhaps some adverse effects apparently associated with aging could be counteracted by efficient strategies, but not others.

Regulation of local sweating in sleep-deprived exercising humans

SummaryThermoregulatory sweating [total body (msw,b), chest (msw,c) and thigh (msw,t) sweating], body temperatures [oesophageal (Toes) and mean skin temperature (Tsk)] and heart rate were investigated in five sleep-deprived subjects (kept awake for 27 h) while exercising on a cycle (45 min at approximately 50% maximal oxygen consumption) in moderate heat (Tair andTwall at 35° C. Themsw,c andmsw,t were measured under local thermal clamp (Tsk,1), set at 35.5° C. After sleep deprivation, neither the levels of body temperatures (Toes,Tsk) nor the levels ofmsw, b,msw, c ormsw, t differed from control at rest or during exercise steady state. During the transient phase of exercise (whenTsk andTsk,1 were unvarying), themsw, c andmsw, t changes were positively correlated with those ofToes. The slopes of themsw, c versusToes, ormsw, t versusToes relationships remained unchanged between control and sleep-loss experiments. Thus the slopes of the local sweating versusToes, relationships (msw, c andmsw, t sweating data pooled which reached 1.05 (SEM 0.14) mg·cm−2·min−1°C−1 and 1.14 (SEM 0.18) mg·cm−2·min−1·°C−1 before and after sleep deprivation) respectively did not differ. However, in our experiment, sleep deprivation significantly increased theToes threshold for the onset of bothmsw, c andmsw, t (+0.3° C,P<0.001). From our investigations it would seem that the delayed core temperature for sweating onset in sleep-deprived humans, while exercising moderately in the heat, is likely to have been due to alterations occurring at the central level.

VISUAL RESOLUTION IN HUMANS FLUCTUATES OVER THE 24H PERIOD

The present experiment was designed to assess daily fluctuations of visual discriminability, a function reflecting the resolution power of the visual sensitivity by measure of a differential threshold. Sixteen subjects underwent a visual discrimination threshold task (using the constant method) in a protocol allowing one point every 2h over the 24h period. The results show that the visual discrimination threshold is low in the morning and increases progressively over the day, reaching a first peak at 22:00. During the night, the same pattern occurs, with low threshold levels at the beginning of the night and high levels at the end. This profile is quite different from that of detection threshold variations, suggesting that the two visual functions are under the control of different underlying mechanisms. Two interpretations could account for this discrepancy. The first relates to different oscillators in the eye for detection and discrimination. The second refers to a possible linkage of visual discriminability with the sleep-wake cycle since threshold measures were systematically low (i.e., high resolution power) after long sleep periods. (Chronobiology International, 17(12), 187–195, 2000)

Humans under showers : thermal sensitivity, thermoneutral sensations, and comfort estimates

Thirty male subjects participated in four experiments under showers to explore the sensitivities to water temperature and to its slow or rapid fluctuations. After having set the water temperature, at constant flow rate, at either a thermoneutral or a preferred level, subjects were asked to detect thermal changes or to report their thermosensory and affective judgments associated with water temperature changes. Results of water temperature, skin temperature, and subjective estimates showed that skin temperature for thermally neutral sensation under a shower were very similar to those observed in air, and such a thermoneutral level produced no discomfort. Preferred water temperature was slightly warmer and led to slightly elevated skin temperatures, warmth, and pleasantness estimates. Skin sensitivity to water thermal changes was very acute during slow and even more acute during rapid thermal transients. The conclusions of the present study are of value in the production of appropriate equipment to provide thermal comfort to people taking showers.

Are OSAS patients impaired in their driving ability on a circuit with medium traffic density

OBJECTIVES Many studies have demonstrated that patients with Obstructive Sleep Apnea Syndrome (OSAS), a very common sleep-related breathing disorder, are usually impaired in their driving ability because of decreased sleep quality. However, most of the simulation procedures in laboratories are designed to create monotonic conditions with low traffic density, if any, thereby leading to a dramatic decrease in performance in OSAS patients because of the lack of stimulation. The aim of this study was therefore to evaluate driving abilities in OSAS patients involved in a driving simulation task with medium traffic density, in order to replicate as far as possible real world conditions. The behavioral and physiological attributes likely to predict driving performance in these patients were also investigated. METHODS After a normal night of sleep, 12 OSAS patients and 8 healthy controls performed 6 driving sessions during a 24-h period of sustained wakefulness. Driving performances (speed, lateral position, distances...) were measured and correlated to sleep parameters and to a waking EEG recorded during the task. RESULTS Compared to controls, patients showed difficulties in speed adjustment. However, they maintained longer inter-vehicle distances, including during overtaking. Their waking EEG, while driving, showed increased spectral power in theta (3.9-7.8Hz) but also in beta (12.7-29.2Hz) activity, alpha power (7.9-12.6Hz) being increased in both groups due to sustained wakefulness. Poor sleep indices were correlated to increased theta and beta activities, as well as to more cautious behavior. DISCUSSION In medium traffic density conditions, driving performance in OSAS patients remained at near normal levels, but with more cautious behavior than controls. This could be the result of a bigger effort to stay awake, as suggested by an increased beta activity in these patients.

Leg skin temperature and thigh sweat output: possible central influence of local thermal inputs

SummaryTo demonstrate whether or not the skin temperature of one lower limb can have an influence on the sweat rate of the contralateral leg, the two legs of five subjects were exposed inside leg-chambers to specific local thermal conditions while sweat rates were measured on both limbs. Three experiments (C I,II,III) of 3 h were carried out: each included two phases A and B. During A, the right leg was not ventilated, while the left leg was (C I) or was not (C II–III) ventilated. During B, the legs were either removed from the leg-chambers (C I) or ventilated inside the chambers at differently controlled levels of leg skin temperature (C II–III). At all times, sweat capsules on both legs measured the sweat rates of local areas of the thigh which were also temperature-controlled. Results showed that, at constant or slightly increased mean skin and core temperatures, the sweat output of one leg could be decreased at constant (C II) or higher local skin temperature (C III) probably due to a decrease in the temperature of the opposite leg. This finding is interpreted as a consequence of a central negative effect, originating from contralateral thermal inputs.

Skin temperatures, thermosensory and pleasantness estimates in case of heterogeneity in the thermal environment

1. 1. Seven thermal conditions were imposed on male sitting subjects (slightly clothed: 0.6 clo). 2. 2. A thermal mannikin was also used to determine the exact operative temperature, T0. 3. 3. Conditions were: uniform (UN: all parameters at 24.5°C, air velocity at 0.15 ms−1), heated ceiling (HC at 45°C), heated floor (HF at 34°C), cold floor (CF at 14°C), two conditions of one cold wall at 6°C (CW1 and CW2 respectively with and without air temperature compensation) and increased air velocity (AV at 0.4 ms−1). 4. 4. Local skin temperatures and answers to questionnaires were obtained. 5. 5. Skin temperature variations were affected by conditions and slight T0 changes. 6. 6. Comfort judgments were fairly well related to T0, especially when expressed as differences between actual non-uniform environment and the uniform one. 7. 7. It is concluded that, in case of non-uniform environments close to thermoneutral zone, thermal comfort or discomfort reflects the climate alterations better than the thermal sensation does.