1 Department of Medicine, University of Chicago, Chicago,
Illinois 60637; 2 Department of Psychology, University of
Metz, Metz, 57045 France; 3 Massachusetts Medical Health
Center, Harvard Medical ...School, Boston 02115; and
4 Department of Psychology, Harvard University, Cambridge,
Massachusetts 02138
This study examines the individual
reproducibility of alterations of subjective, objective, and EEG
measures of alertness during 27 h of continuous wakefulness and
analyzes their interrelationships. Eight subjects were studied twice
under similar constant-routine conditions. Scales and performance tasks
were administered at hourly intervals to define temporal changes in
subjective and objective alertness. The wake EEG was recorded every
2 h, 2 min with eyes open and 2 min with eyes closed. Plasma
glucose and melatonin levels were measured to estimate brain glucose
utilization and individual circadian phase, respectively.
Decrements of subjective alertness and performance deficits were found
to be highly reproducible for a given individual. Remarkably, there was
no relationship between the impairments of subjective and objective
alertness. With increased duration of wakefulness, EEG activity with
eyes closed increased in the delta range and decreased in the alpha
range, but the magnitudes of these changes were also unrelated. These
findings indicate that sleep deprivation has highly reproducible, but
independent, effects on brain mechanisms controlling subjective and
objective alertness.
subjective alertness; attention; trait dependence; circadian
rhythm
Image segmentation is a computer vision task aiming to establish a probabilistic mapping between individual pixels (2D) or voxels (3D) in an input image and a set of predefined semantic categories ...with reference to domain-specific knowledge. When applied to medical images, e.g. Magnetic Resonance Imaging (MRI), it allows delineation between healthy and abnormal tissue. Despite challenges due to lesion morphological heterogeneity, segmentation of brain tumours has the potential to streamline otherwise time-consuming manual annotation. Whereas brain tumour segmentation has continually advanced incorporating innovative deep learning methods, heuristics normally employed by radiologists have often been neglected. The focus of nearly all tumour segmentation articles thus far on 3D isotropic research-grade scans has also led to results of unknown generalisability to hospital-quality data. In order to address these gaps, this study has coalesced modern deep learning methods and clinical-driven priors into an optimised segmentation pipeline evaluated on clinical data at a large neurology and neurosurgery tertiary centre.
The only well documented effect of light exposure on endocrine function is the suppression of nocturnal melatonin. Bright light exposure has behavioral effects, including the alleviation of ...sleepiness during nocturnal sleep deprivation. The present study examines the effects of bright light on the profiles of hormones known to be affected by sleep deprivation (TSH) or involved in behavioral activation (cortisol). Eight healthy men participated each in three studies involving 36 h of continuous wakefulness. In one study, the subjects were exposed to constant dim light (baseline). In the two other studies, dim light exposure was interrupted by a 3-h period of bright light exposure either from 0500-0800 h (early morning study) or from 1300-1600 h (afternoon study). Blood samples were obtained every 15 min for 24 h to determine melatonin, cortisol, and TSH concentrations. Alertness was estimated by the number of lapses on two computerized vigilance-sensitive performance tasks. The early morning transition from dim to bright light suppressed melatonin secretion, induced an immediate, greater than 50% elevation of cortisol levels, and limited the deterioration of alertness normally associated with overnight sleep deprivation. No effect was detected on TSH profiles. Afternoon exposure to bright light did not have any effect on either hormonal or behavioral parameters. The data unambiguously demonstrate an effect of light on the corticotropic axis that is dependent on time of day.
1 Department of Medicine, University of Chicago, Chicago,
Illinois 60637; and 2 Center for Biological Rhythms and
Laboratory of Experimental Medicine, Université Libre de
Bruxelles, B-1070 ...Brussels, Belgium
In normal men, the majority of GH secretion occurs in a single
large postsleep onset pulse that is suppressed during total sleep
deprivation. We examined the impact of semichronic partial sleep loss,
a highly prevalent condition, on the 24-h growth hormone profile.
Eleven young men were studied after six nights of restricted bedtimes
(0100-0500) and after 7 nights of extended bedtimes
(2100-0900). Slow-wave sleep (SWS) was estimated as the duration
of stages III and IV. Slow-wave activity (SWA) was calculated as
electroencephalogram power density in the 0.5- to 3-Hz frequency
range. During the state of sleep debt, the GH secretory pattern
was biphasic, with both a presleep onset "circadian" pulse and a
postsleep onset pulse. Postsleep onset GH secretion was negatively
related to presleep onset secretion and tended to be positively
correlated with the amount of concomitant SWA. When sleep was
restricted, both SWS and SWA were increased during early sleep.
Unexpectedly, the increase in SWA affected the second, rather than the
first, SWA cycle, suggesting that presleep onset GH secretion may have limited SWA in the first cycle, possibly via an inhibition of central
GH-releasing hormone activity. Thus neither the GH profile nor the
distribution of SWA conformed with predictions from acute sleep
deprivation studies, indicating that adaptation mechanisms are
operative during chronic partial sleep loss.
growth hormone secretion; slow-wave activity; sleep deprivation
Decreased levels of physical and social activity associated with aging can be particularly pronounced in residents of assisted living facilities. Reduced exposure to important behavioral and ...time-giving cues may contribute to the age-related changes in circadian rhythmicity and sleep. The present study was conducted to test the hypothesis that an enforced schedule of structured social and physical activity (0:900 to 10:30 and 19:00 to 20:30 daily for two weeks) can have beneficial effects on circadian rhythmicity, nocturnal sleep, daytime functioning, mood, and vigor. The subjects were 14 elderly residents of continued-care retirement facilities while a similar group of 9 elderly residents served as controls. The group exposed to structured activities had increased amounts of slow-wave sleep and demonstrated improvement in memory-oriented tasks following the intervention. Conversely, no significant changes were noted in the amplitude and phase of the body temperature rhythm or in subjective measures of vigor and mood. These results indicate that short-term exposure to structured social intervention and light physical activity can significantly improve memory performance and enhance slow-wave sleep in older adults without alterations to the circadian phase or amplitude of body temperature. This is the first report to demonstrate that low intensity activity in an elderly population can increase deep sleep and improve memory functioning. The high degree of interest in these activities paired with the simple nature of the tasks makes this a potentially practical intervention which can be adapted for both community dwelling and assisted-living elders.
Previous studies indicate that the advance region of the
tau mutant hamster's phase-response curve (PRC) to non-photic stimuli, such as NPY and wheel pulses, is characterized by earlier timing and ...increased amplitude in comparison with that of wild-type animals. Since, recent evidence suggests that serotonergic pathways may play an important role for the non-photic phase resetting of the rodent circadian pacemaker, PRCs to the serotonin (5-HT) agonist, 8-OH-DPAT (5 mg/kg i.p.), were generated in both wild-type and
tau mutant hamsters kept in constant darkness. The results indicate that the
tau mutation is associated with changes in the timing, but not the amplitude of the advance region of the PRC to 8-OH-DPAT and suggest that serotonergic agents and other non-photic or activity-inducing stimuli may share some common mechanisms for resetting the phase of the rodent circadian pacemaker.
The only well documented effect of light exposure on endocrine function
is the suppression of nocturnal melatonin. Bright light exposure has
behavioral effects, including the alleviation of ...sleepiness during
nocturnal sleep deprivation. The present study examines the effects of
bright light on the profiles of hormones known to be affected by sleep
deprivation (TSH) or involved in behavioral activation (cortisol).
Eight healthy men participated each in three studies involving 36
h of continuous wakefulness. In one study, the subjects were exposed to
constant dim light (baseline). In the two other studies, dim light
exposure was interrupted by a 3-h period of bright light exposure
either from 0500–0800 h (early morning study) or from 1300–1600 h
(afternoon study). Blood samples were obtained every 15 min for 24
h to determine melatonin, cortisol, and TSH concentrations. Alertness
was estimated by the number of lapses on two computerized
vigilance-sensitive performance tasks. The early morning transition
from dim to bright light suppressed melatonin secretion, induced an
immediate, greater than 50% elevation of cortisol levels, and limited
the deterioration of alertness normally associated with overnight sleep
deprivation. No effect was detected on TSH profiles. Afternoon exposure
to bright light did not have any effect on either hormonal or
behavioral parameters. The data unambiguously demonstrate an effect of
light on the corticotropic axis that is dependent on time of day.
Study of ionization losses in He-based gas mixtures Borsato, E; Colecchia, F; Dal Corso, F ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/1999, Letnik:
423, Številka:
2
Journal Article
Recenzirano
Helium based gas mixtures are particularly interesting since they have a good tracking resolution because of the reduced multiple scattering. We have studied the differential energy loss d
E/d
x in ...several mixtures, He–isobutane and He–ethane. We present results from measurements performed with electrons, pions and protons in the momentum range between 1 and 5
GeV/
c obtained in a prototype drift chamber with a 3
cm cell. The results show that helium performs well in measuring energy losses for charged particles.
In normal men, the majority of GH secretion occurs in a single large postsleep onset pulse that is suppressed during total sleep deprivation. We examined the impact of semichronic partial sleep loss, ...a highly prevalent condition, on the 24-h growth hormone profile.
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