Biomedical subjects
Publications and source records attributed to D F Dinges.
The authors investigated habituation of the eye-blink component of the startle reflex to repeated affectively neutral tactile and auditory stimuli in nine subjects with posttraumatic stress disorder and nine controls. Each group showed rapid habituation in both tactile and auditory modalities.
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Napping can enhance alertness during sustained wakefulness, but the importance of the temporal placement of the nap between days and within the circadian cycle remains controversial. To resolve these issues, a between-groups study was conducted with 41 healthy, young adults permitted a 2-h nap at one of five times during a 56-h period otherwise devoid of sleep. Naps were placed 12 h apart, near the circadian peak (P) or trough (T), and were preceded by 6, 18, 30, 42, or 54 h of wakefulness. Visual reaction time (RT) performance, Stanford Sleepiness Scale (SSS) ratings, and sublingual temperature were assessed every few hours throughout the 56 h, which took place in an environment free of time cues. All groups displayed a circadian-modulated decline in RT measures and increases in SSS functions as sleep loss progressed. A nap placed at any time in the protocol improved RT performance, particularly in the lapse domain, but not SSS ratings. Comparisons within groups of circadian temperature cycles for the first versus second day of the protocol indicated that early naps (P6, T18, P30) tended to prevent the mean drop in temperature across days. The earlier naps (P6, T18) yielded more robust and longer lasting RT performance benefits, which extended beyond 24 h after the naps, despite the fact that they were comprised of lighter sleep than later naps. Circadian placement of naps (P vs. T) did not affect the results on any parameter. In terms of temporal placement, therefore, napping prior to a night of sleep loss is more important for meeting subsequent performance demands than is the circadian placement of the nap. SSS ratings suggest that the napper is not aware of these performance benefits. Because the longest lasting RT gains followed early naps, which were composed of less deep sleep than later naps, napping during prolonged sleep loss may serve to prevent sleepiness more readily than it permits recovery from it.
Studies of experimentally altered human sleep-wake cycles have shown that rapid eye movement (REM) sleep propensity exhibits a circadian periodicity, while slow wave sleep (SWS) is primarily responsive to the duration of prior wakefulness. What is not known is the extent to which REM sleep continues to show a circadian pattern under intense sleep pressure, and the extent to which SWS remains responsive to prior wakefulness at opposite phases of the circadian cycle. These questions were addressed by permitting healthy young adults a 2 h nap opportunity at opposite phases of the circadian cycle and with varying amounts of prior wakefulness, during a 54 h trial in a laboratory environment free of time cues. Three groups slept near the circadian peak (15.00 h) in the diurnal activity cycle, preceded by either 6, 30, or 54 h of prior wakefulness. Two other groups had naps near the circadian trough (03.00 h), midway between the peak naps and preceded by either 18 or 42 h of wakefulness. Comparisons both between and within groups revealed that latencies to sleep onset and to SWS decreased, while stage 4 sleep increased markedly in response to prior wakefulness up to 30 h, without any effect from the circadian placement of the nap. REM sleep propensity, as measured by the number of naps with REM and the amount of REM sleep among those naps that contained REM, was affected only by the circadian phase of the nap, with trough naps containing significantly less REM. Thus, no amount of sleep pressure changed the circadian phase-dependent expression of REM, and SWS remained wake-responsive at both phases of the diurnal cycle.
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Newborn infants, chronically exposed in utero to low doses of methadone with or without concomitant heroin, display more rapid eye movement sleep and less quiet sleep than control infants, while babies fetally exposed to both opiates and nonopiates have less organization of sleep states. Other perinatal factors, such as birth weight and gestational age, are related more to the amount of fetal drug exposure than to the type.
The middle and the late components of auditory evoked potentials were alternately recorded in sequential sets from 28 adults, both awake and asleep. Sleep was induced by secobarbital and was monitored for depth. 1000 c/sec tone pips in one laboratory or filtered clicks in the other were delivered at 10, 20 or 30 dB sensation level. Control collections without stimulation were included. For the middle responses a single simple scoring template and one set of voltage criteria could be used for all stages of waking and sleeping. For late responses different templates and voltage criteria were needed. Estimates of the threshold of detection of the evoked potentials were based on the percentage of clearly positive responses was often not attained at 30 dB SL, i.e., the threshold was indeterminate. In light sleep and awake the middle responses of most subjects gave thresholds more sensitive than the late by 10-15 dB and also fewer indeterminate trials. The results in our two laboratories agreed closely in spite of differences in equipment and details of procedure. The relatively low thresholds of the middle responses (median 17.5 dB SL awake and 15 dB SL in light sleep) suggest that the middle responses must be considered seriously for use in clinical electric response audiometry, even though one of the 28 subjects failed to yield any identifiable middle responses.
This study was a 19-week prospective conducted to determine the effectiveness of a self-hypnosis/relaxation intervention to relieve symptoms of psychological distress and moderate immune system reactivity to examination stress in 35 first-year medical students. Twenty-one subjects were randomly selected for training in the use of self-hypnosis as a coping skill and were encouraged to practice regularly and to maintain daily diary records related to mood, sleep, physical symptoms, and frequency of relaxation practice. An additional 14 subjects received no explicit training in stress-reduction strategies, but completed similar daily diaries. Self-report psychosocial and symptom measures, as well as blood draws, were obtained at four time points: orientation, late semester, examination period, and postsemester recovery. It was found that significant increases in stress and fatigue occurred during the examination period, paralleled by increases in counts of B lymphocytes and activated T lymphocytes, PHA-induced and PWM-induced blastogenesis, and natural killer cell (NK) cytotoxicity. No immune decreases were observed. Subjects in the self-hypnosis condition reported significantly less distress and anxiety than their nonintervention counterparts, but the two groups did not differ with respect to immune function. Nevertheless, within the self-hypnosis group, the quality of the exercises (ie, relaxation ratings) predicted both the number of NK cells and NK activity. It was concluded that stress associated with academic demands affects immune function, but immune suppression is not inevitable. Practice of self-hypnosis reduces distress, without differential immune effects. However, individual responses to the self-hypnosis intervention appear to predict immune outcomes.
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