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Biomedical subjects

A Muzet

Publications and source records attributed to A Muzet.

At least 19 recordsLinked to original sources
PubMed2005

Oculomotor changes due to road events during prolonged monotonous simulated driving.

The possible influence of occuring external events on driver attention and vigilance level was assessed during a prolonged simulated driving task. Special attention was given to the duration of the task, as well as to the influence of time of day and of individual factors. Thirty six subjects drove for two hours. Blinking activity and eye movements associated with glances to the speedometer were recorded during the entire driving task and particularly during specific road events. During significant events, blinking and ocular activity decreased, attesting a higher attention of the driver. With increased duration of driving, the reduction in blinking and ocular activity was progressively smaller for the less significant events, indicating a reduction in attention. During driving, women blinked more frequently than men. With increased duration of driving, drivers adopted different behavioural strategies depending on their age and sex to reach a safe and adapted method of driving.

Adult↗
PubMed2003

Effects of a moderate nocturnal cold stress on daytime sleep in humans.

The effects of a nocturnal exposure to a cool environment on daytime recovery sleep was studied in eight young (20-25 years old) healthy volunteers. A set of standardized clothing (KSU ensemble type) was provided to each individual (estimated total thermal resistance: 0.6 clo). The subject kept awake was passively exposed from 22.30 to 07.30 hours to environments perceived as neutral (N) and comfortable or slightly cold (C) and uncomfortable. They were then allowed to sleep ad libitum (light out at 08.00 hours) under thermoneutral conditions (air temperature: 21 degrees C to 22 degrees C; clothing: cotton tee-shirt and pajama-pants; covering: one cotton sheet and one wool blanket). Sleep was recorded and scored according to the Rechtchaffen and Kales standard procedures. Esophageal temperature (T(es)) was recorded from 21.30 hours until the end of sleep. The nocturnal drops in T(es) were significantly different between N and C (p<0.01), this difference disappearing during sleep. No statistical difference was found between conditions for most of the sleep variables. Compared to N however, C resulted in a significant increase in rapid eye movement (REM) sleep duration (+35%, p<0.01) during the subsequent daytime sleep. It is hypothesized that the REM-sleep increase induced by the exposure to moderate cold is due to the thermal discomfort stress consciously perceived by the subject.

Adaptation, Physiological↗
PubMed2001

Innovative working schedule: introducing one short nap during the night shift.

In order to test the possible long-term effects of the implementation of a short nap during night shifts, an experiment was conducted over a period of 1 year with 12 volunteer shiftworkers operating in an industrial plant. They were authorized, under certain conditions, to use individual sleeping areas, for a maximum of 1 hour, between 23h30 and 3h30. The participants were asked to fill in a short questionnaire every day during the entire study. The questions concerned the schedule of the main sleep period, the afternoon nap and the night-time nap, if any, as well as the evaluation of mood and the quality of work. This daily questionnaire was supplemented by an extensive questionnaire applied every 2 months in order to assess the main changes introduced in the life of the participants by this new working schedule. Results showed that this new organization introduced a general satisfaction about the quality and the easiness of the work at night. The vigilance level was considered to be higher during the hours following the nap. The efficacy of the nap time progressively increased for most subjects. The general quality of life improved for most subjects. While a few of them considered that falling asleep was less easy on the following morning at home, the statistical analysis did not show any detrimental effect of the short rest period on the length of the immediately consecutive main sleep period. However, different statistical analyses allow us to reveal significant differences between the main sleep durations following the night shift compared with those following both the afternoon shift and the resting period. The main sleep duration following the night shift was not statistically different from that of the morning shift. These results are very encouraging. A short nap during the night shift can be considered as a positive way to counteract the low level of vigilance that normally occurs during the late part of the night.

Adult↗
PubMed2001

Variations of the level of vigilance and of behavioural activities during simulated automobile driving.

During a monotonous activity, certain behaviours occur that are not necessary to the performance of the task. These are subsidiary or collateral activities. Our purpose was to find out if the number of these behaviours tends to increase during a monotonous and prolonged activity. A study was carried out with 17 subjects performing a 2-h car drive on the Vigilance Analysis Driving Simulator. An analysis of the drivers' behaviour and of their state of vigilance allowed us to confirm the existence of a relation between the occurrence of these behaviours and the variations of the level of arousal. In addition, we determined for all produced behaviours, those that preceded, those that coincided with, and those that followed low vigilance phenomena. These results were interpreted in terms of behavioural signs, precursory of low vigilance, indicative of low vigilance, or reactivating the driver.

Adult↗
PubMed2001

Defining the states of consciousness.

Consciousness remains an elusive concept due to the difficulty to define what has been regarded for many years as a subjective experience, therefore irrelevant for scientific study. Recent development in this field of research has allowed to provide some new insight to a possible way to define consciousness. Going through the extensive literature in this domain, several perspectives are proposed to define this concept. (1) Consciousness and Attention may not reflect the same process. (2) Consciousness during wake and sleep may not involve the same mechanisms. (3) Besides physiological states of consciousness, human beings can experience modified states of consciousness either by self-training (transcendental meditation, hypnosis, etc.) or by drug intake (hallucinogens, anaesthetics, etc.). Altogether, we address the question of a more precise terminology, given the theoretical weight words can convey. To this respect, we propose different definitions for concepts like consciousness, vigilance, arousal and alertness as candidates to separate functional entities.

Animals↗
PubMed2001

Morning and evening TSH response to TRH and sleep EEG disturbances in major depressive disorder.

1. The aim of this study was to investigate hypothalamo-pituitary-thyroid axis (HPTA) functioning and sleep EEG disturbances in major depressive disorder. 2. Thyroid function was evaluated by determination of TSH levels before and after 8 AM and 11 PM TRH administration on the same day in a sample of 113 consecutively-admitted DSM-IV major depressed inpatients (72 females aged 44.3 +/- 13.0 and 41 males aged 45.7 +/- 10.7) that underwent sleep EEG recordings. 3. A blunted TSH response occurred in 15.9% for 8 AM deltaTSH (maximum increment above baseline at the 8 AM TRH challenge), in 39.8% for 11 PM deltaTSH and in 77% for deltadeltaTSH (difference between 11 PM deltaTSH and 8 AM deltaTSH). A negative correlation between deltadeltaTSH and duration of awakenings after sleep onset, and a shorter sleep onset latency in patients with a blunted 11 PM deltaTSH were found, but these two significant relationships disappeared after controlling for the effects of gender and age. 4. The present findings do not support the hypothesis that, in major depression, HPTA dysfunctioning, as reflected in TSH response to TRH, may be related to sleep EEG disturbances.

Adult↗
PubMed2000

High frequency waking EEG: reflection of a slow ultradian rhythm in daytime arousal.

The ultradian dynamics of the human waking EEG was studied using a short visual fixation task repeated every 10 min throughout the daytime. The EEG spectra obtained from the tasks were assessed for time effect and ultradian periodicity. Fronto-central EEG high frequency powers (22.5-44.5 Hz) decreased at the time of the midafternoon vigilance dip (14.00-17.00 h) along with slight concomitant increases in parietal alpha (7.5-13.5 Hz) and delta (1-3 Hz) powers. A slow ultradian rhythm with a 3-4 h periodicity strongly modulated EEG power in all frequency bands between 1 and 44.5 Hz. The high frequency waking EEG may well reflect the activity of a brain arousal process underlying maintenance of the waking state probably throughout the 24 h cycle.

Activity Cycles↗
PubMed2000

Effects of a nocturnal environment perceived as warm on subsequent daytime sleep in humans.

We studied the influence of a nocturnal environment perceived as warm on the subsequent daytime sleep of healthy human subjects (20-25 years old). From 00:00 to 8:00, they were kept awake and exposed to either a thermoneutral and comfortable (CN) or a warm and uncomfortable (EW) environment, as assessed by the predicted mean vote/percentage of persons dissatisfied questionnaire (PMV/PPD). The subjects then slept from 8:00 to 14:00 in a thermoneutral environment. Sleep was scored according to the Rechtschaffen and Kales criteria. Rectal temperature was recorded from 22:00 to the end of the sleep period. Compared to CN, a significant but moderate hyperthermia (0.3-0.4 degrees C) occurred rapidly in EW, and was maintained throughout the night. This modest difference disappeared during subsequent sleep spent at thermal comfort. Exposure to a warm uncomfortable environment before bedtime significantly increased the duration (+37%) and percentage of rapid eye movement sleep (REMS). This hypnic response could be due to interactions occurring between thermoregulatory, circadian, and sleep mechanisms. It could also be ascribed to synergic actions of the neurophysiological (among others, involving the hypothalamo-pituitary-adrenal axis) and psychological (involving memory processing) processes developed when the organism faces a moderate stress.

Adult↗
PubMed2000

Changes in EEG power density during sleep laboratory adaptation in depressed inpatients.

BACKGROUND: The aim of the present study was to evaluate the first-night effect in depressed inpatients, using standard sleep measures as well as all-night spectral analysis of the sleep electroencephalogram (EEG). METHODS: Eighteen drug-free, depressed inpatients were studied for 3 consecutive nights in the hospital sleep laboratory. RESULTS: Visual sleep scoring results showed a slight but measurable first-night effect, characterized by a reduction of rapid eye movement (REM) sleep amount and increased wakefulness. Sleep EEG spectral analysis showed significantly reduced delta (p <.01) and theta (p <.05) power density in non-REM (NREM) sleep of the first night compared with that of the second and third nights. These differences were limited to the early part of the sleep period, a time during the night that is particularly vulnerable to the effects of depressive disorder. In contrast to the NREM sleep findings, spectral REM variables studied did not significantly vary across the three nights. CONCLUSIONS: The results obtained suggest that first-night data should not be simply discarded but could be used in subsequent analyses and could be considered useful in the evaluation of the sleep of depressed patients.

Adult↗
PubMed2000

[The characteristics of sleep-wake rhythm in adolescents aged 15-20 years. A survey made at school during ten consecutive days].

UNLABELLED: Adolescents' fatigue is a worrying subject. PATIENTS AND METHOD: A survey was carried out over a period of ten days (a school week between two weekends). Through a daily questionnaire, 386 adolescents aged 15-20 years were asked about sleep onset and offset, time delay of sleep onset, quality of sleep, daytime sleepiness and naps. RESULTS: The results confirmed that the length of sleep was lessened during weekdays. This duration was one hour shorter than on Saturday nights or during holidays. However, a significant delay occurs in sleep onset on Saturday nights and sleep offset on Sunday mornings, which represents the main irregularity in the sleep schedule. Poor quality of sleep is due to difficulties in sleep onset (16%) and night awakenings (39%). Daytime sleepiness is reported by 38% of the adolescents, and many of them have a nap on Sundays, or other days of the week. Daytime activities (out-of-school sports, particularly) and evening activities were studied as well as the use of hypnotics and stimulants. CONCLUSION: This work stresses sleep insufficiency during the week at school, changes in sleeping patterns during weekends, and sometimes poor quality of sleep. Similar facts have already been found in children, and this may explain the consequences on the life and behaviour of adolescents. The population has to be informed about the effects of sleep on health.

Adolescent↗
PubMed2000

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.

Adult↗
PubMed2000

Variation of visual detection over the 24-hour period in humans.

A circadian rhythm for visual sensitivity has been intensively assessed in animals. This rhythm may be due to the existence of a circadian clock in the mammalian eye, which could account for fluctuating sensitivity to light over the day in certain species. However, very few studies have been devoted to the human visual system. The present experiment was designed to assess a possible rhythm of visual sensitivity using a psychophysical method over the whole 24h period. Twelve subjects underwent visual detection threshold measures in a protocol that allowed one point every 2h. The results show that the visual detection threshold changes over the 24h period, with high thresholds in the morning, a progressive decrease over the day and the early night, and an increase during the last part of the night. These data suggest that a circadian rhythm influences visual sensitivity to mesopic luminance in humans.

Adult↗
PubMed1999

Electroencephalographic characterization of brain dopaminergic stimulation by apomorphine in healthy volunteers.

Apomorphine, a dopamine receptor agonist (given in a dose of 0.75 mg s.c.), was administered to 8 healthy volunteers; electroencephalograph (EEG) and event-related potential (ERP) mapping were performed before dosing and 0.5, 1.5 and 2.5 h after dosing. Apomorphine caused an overall increase in beta activity at time 0.5 h in both absolute and relative energy; P300 and CNV ERPs were not significantly altered, although a tendency towards increased P300 latency was seen. The results confirm that the EEG mapping technique is sufficiently sensitive to monitor dopaminergic neurochemical stimulation by means of apomorphine. This could lead to a new, non-invasive and repeatable method for monitoring central neuronal systems which is more convenient to apply repeatedly than for example positron emission tomography techniques. Furthermore, electrophysiological techniques undoubtedly constitute an alternative to classical neuroendocrinological methods, allowing a more direct assessment of central nervous system neurotransmission. Finally, these EEG approaches could lead to better characterization of drugs acting on dopaminergic pathways, such as antipsychotics.

Adult↗
PubMed1999

Diurnal pattern of luminance discrimination in humans.

The visual discrimination threshold can be considered as an image of the resolution power of the visual system. Measured with a psychophysical method, it shows a diurnal pattern with a low threshold in the morning, i.e., high sensitivity and an increase in the afternoon that persists until the early evening.

Adult↗
PubMed1998

Cortisol secretion is related to electroencephalographic alertness in human subjects during daytime wakefulness.

To determine whether human hypothalamo-pituitary-adrenal axis activity is related to the alertness level during wakefulness, 10 healthy young men were studied under resting conditions in the daytime (0900-1800 h) after an 8-h nighttime sleep (2300-0700 h). A serial 70-sec gaze fixation task was required every 10 min throughout the daytime experimental session. The corresponding waking electroencephalographic (EEG) segments were submitted to quantitative spectral analysis, from which EEG beta activity (absolute power density in the 13-35 Hz frequency band), an index of central alertness, was computed. Blood was collected continuously through an indwelling venous catheter and sampled at 10-min intervals. Plasma cortisol concentrations were measured by RIA, and the corresponding secretory rates were determined by a deconvolution procedure. Analysis of individual profiles demonstrated a declining tendency for EEG beta activity and cortisol secretory rate, with an overall temporal relationship indicated by positive and significant cross-correlation coefficients between the two variables in all subjects (average r=0.565, P < 0.001). Changes in cortisol secretion lagged behind fluctuations in EEG beta activity, with an average delay of 10 min for all the subjects. On the average, 4.6+/-0.4 cortisol secretory pulses and 4.9+/-0.5 peaks in EEG beta activity were identified by a detection algorithm. A significant, although not systematic, association between the episodes in the two variables was found: 44% of the peaks in EEG beta activity (relative amplitude, near 125%; P < 0.001) occurred during an ascending phase of cortisol secretion, cortisol secretory rates increasing by 40% (P < 0.01) 10-min after peaks in EEG beta activity. However, no significant change in EEG beta activity was observed during the period from 50 min before to 50 min after pulses in cortisol secretion. In conclusion, the present study describes a temporal coupling between cortisol release and central alertness, as reflected in the waking EEG beta activity. These findings suggest the existence of connections between the mechanisms involved in the control of hypothalamo-pituitary-adrenal activity and the activation processes of the brain, which undergoes varying degrees of alertness throughout daytime wakefulness.

Adult↗
PubMed1997

Temporal relationships between pulsatile cortisol secretion and electroencephalographic activity during sleep in man.

A temporal link between slow wave sleep and low or decreasing cortisol release has been previously demonstrated. This relationship was re-evaluated in 15 healthy male subjects using spectral analysis of their sleep electroencephalogram (EEG). EEG activity in the delta, theta, alpha and beta bands was cross-correlated with cortisol secretory rates at 10-min intervals. For the period of pulsatile cortisol secretion, an inverse relationship was found with the delta band with an average cross-correlation coefficient of -0.505 (P < 0.0001). Variations in cortisol secretory rates coincided with or anticipated opposite variations in delta wave activity by 10 or 20 min. A significant positive correlation was found with theta activity, but alpha and beta bands did not elicit any systematic association with cortisol profiles. These results demonstrate a temporal association between cortisol secretory pulses and delta wave activity in man, suggesting the existence of a central control common to both variables.

Adult↗
PubMed1997

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.

Adult↗