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    We g with stories for trying their gap conditions at that classroom and for that stick preview settings are more of a simple concentration for them. Thus, the question remains as to whether an abnormally long spontaneous period length may contribute to the constellation of symptoms that define DSPD. We describe the sleep and body temperature rhythms of an individual with DSPD studied in temporal isolation. The DSPD subject was a year-old male graduate student who reported a lifelong history of very late bedtimes and an inability to awaken refreshed until the early afternoon.

    Physical and psychiatric screenings revealed no pathology. As part of an ongoing study to assess circadian rhythmicity in older vs younger individuals, data were obtained from 3 healthy normal subjects close to the DSPD subject's age 2 females, aged 19 and 26, and a male, aged All were compensated for participation. Following enrollment in the study, subjects maintained daily sleep logs for 2 consecutive weeks while living at home and continuing their usual daily activities. They then underwent a laboratory session that continued for 23 consecutive days and nights.

    Throughout their stay in the lab, subjects lived in a studio apartment that was shielded from any cues to time of day. Illumination was provided by desk and floor lamps situated around the apartment. Illumination in different areas of the apartment ranged from 10 lux to lux, with a typical level e.

    The first 2 nights in the lab were used for adaptation and to screen for sleep disorders i. This was followed by a 4-day entrainment period, during which sleep and rising times, as well as meal times, were circumscribed.

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    For the next 17 days, subjects were permitted to self-select bedtimes and wake times and to eat meals at their discretion. Subjects were allowed to engage in activities of their choice, with the exception of strenuous exercise, and they were not permitted to nap. Sleep was recorded polygraphically on the adaptation and entrainment nights.

    EEG, EOG, and EMG were recorded continuously throughout the free-run portion except when subjects showered , via a telemetry system Biosentry, Torrance, CA that permitted freedom of movement around the isolation apartment. Body core temperature was also recorded continuously, in 2-minute epochs, using a rectal thermistor, connected to an ambulatory data storage device Minilogger, Minimitter, Inc. Bend, OR. Closed-circuit TV permitted observation of subjects throughout the laboratory session, and an intercom system permitted communication when necessary.

    Sleep records were scored in second epochs using standard criteria. Summary sleep measures were obtained by averaging data from sleep episodes recorded on 15 of the day free-run period for the DSPD subject data from 2 days were not available due to equipment malfunction and from 48 of 54 free-run sleep episodes for the normal controls. Data from the first night were not used because subjects had circumscribed bedtimes.

    Raw body temperature data were edited for artifact e. Curve-fitting techniques using a harmonic regression model were used to estimate parameters of the temperature rhythm, including the daily minimum tmin. Linear regression on the daily time of tmin was used to calculate spontaneous period length tau. All comparisons were made using one-way and two-way for halves of the night analyses ANOVA, with the exception of sleep onset latency. All P values are based on two-tailed tests of significance. The DSPD subject's home sleep log confirmed his report of very late sleep and waking times.

    His mean estimated sleep latency was 50 minutes, resulting in an average sleep period time of 9. On all but one day, the subject used an alarm clock to awaken. The day on which an alarm clock was not used, the subject reported a bedtime of and an awakening time of That the subject's circadian system was delayed was verified further by temperature data obtained during the entrainment portion of the lab session.

    Because his scheduled wake time in the lab was , the subject's temperature minimum was masked by rising from bed i. For the entire day interval, the subject exhibited an average tau of This is compared to an average tau of Timing of spontaneous sleep periods bars and daily temperature minima inverted triangles for the subject with DSPD dark and for a normal year-old male subject light gray , across 17 days of temporal isolation.

    The DSPD subject exhibited a spontaneous period length tau of The figure also shows the altered phase relationship between sleep and body temperature in the DSPD subject see text and Figure 2 for details. As shown in Figure 2 , the phase relationship between the subject's sleep and body temperature was also altered relative to normal subjects. Whereas, the average phase angle between sleep onset and tmin was 1.

    Conversely, sleep offset occurred more closely to tmin in the DSPD subject than in the normal subjects 5. Average phase relationship between the timing of spontaneous sleep open bars and the minimum of body temperature tmin; vertical line for the DSPD subject top and for three similarly-aged control subjects studied under identical conditions.

    Shown are average intervals and standard error from sleep onset to tmin 3. Table 1 shows the comparison of sleep between the DSPD subject and the 3 comparison subjects. Based on data averaged over 14 sleep periods for the DSPD subject and 47 sleep episodes for the comparison subjects, the DSPD subject exhibited a significantly longer sleep onset latency, significantly greater wake time after sleep onset WASO , significantly less stage 2 sleep and significantly poorer sleep efficiency. To our knowledge, this is the first report of a documented case of DSPD studied under conditions in which spontaneous period length tau could be measured.

    The results suggest that the phase disturbances that characterize DSPD under entrained conditions may be the consequence of a fundamental abnormality of the circadian timing system. For the subject studied here, this was reflected not only in a long tau , but also in an altered phase relationship between the timing of sleep and the circadian rhythm of body core temperature.

    Although the latter finding has been reported previously in patients studied in entrained conditions, 6 , 7 that such an alteration was also observed in temporal isolation supports the notion that the etiology of DSPD goes beyond simply a reduced capacity to achieve and maintain the appropriate phase relationship between sleep timing and the hour day. Rather, the disorder may also reflect a fundamental inability of the endogenous circadian timing system to maintain normal internal phase relationships among physiological systems, and to properly adjust those internal relationships within the confines of the hour day.

    In normal subjects, the phase relationship between sleep and temperature changes in temporal isolation relative to that observed under entrained conditions 8 : in isolation, tmin tends to occur toward the beginning of sleep. Under entrained conditions, tmin occurs, instead, toward the end of the sleep period, a change in phase angle of several hours. A comparison of our findings with those from DSPD patients studied in entrainment 6 , 7 suggests that those with DSPD may have a reduced capacity to achieve such a change in phase angle in response to entrainment.

    Our findings further suggest, possibly as a consequence of these altered internal phase relationships, that the quality of sleep in DSPD may be substantially poorer than that of normal subjects, even when bedtimes and wake times are self-selected. Our DSPD subject exhibited an average sleep onset latency twice that of the 3 control subjects and almost twice the amount of wakefulness after sleep onset WASO as control subjects, resulting in significantly poorer sleep efficiency.

    Also, the temporal distribution of slow wave sleep was significantly altered in the DSPD subject. This finding may suggest that, in addition to abnormal circadian clock function, DSPD may be characterized by alteration s in the homeostatic regulation of sleep, as well. Specifically, the rate with which Process S 9 is depleted during sleep may be slowed.

    This could, conceivably, contribute to the excessive sleep inertia upon awakening that is often reported by DSPD sufferers. The few published reports of polysomnographically recorded sleep in DSPD are in general agreement with those reported here. For example, in their initial description of the disorder, Weitzman and coworkers reported polysomnographic sleep measures in 6 individuals diagnosed with DSPD.

    Thorpy et al 11 reported similar results for 9 adolescent DSPD patients mean sleep latency: Though quite limited in terms of the total number of DSPD patients studied, such data seem to contradict the notion that DSPD is merely a disorder of sleep timing , rather than a disorder of the sleep system itself.

    If additional studies support these results, a reassessment of the nature of sleep in DSPD, the diagnostic guidelines derived there from, as well as, revised approaches to treatment of the disorder, may be warranted. It is unlikely that light exposure during temporal isolation contributed to the long period length observed in our DSPD subject.

    Circadian Rhythm and Your Brain's Clock

    As mentioned, illumination was maintained at well below 50 lux in the isolation apartment. Moreover, as there is no reason to assume that control subjects were exposed to light in a fundamentally different manner than the DSPD subject, any impact of light would be expected to be consistent across all subjects. Nevertheless, we cannot entirely rule out the possibility that light acted differentially on the endogenous clock of our DSPD subject, resulting in the longer tau.