|Table of Contents|
Table of Contents
List of Tables
List of Figures
Chapter 1. Introduction
Chapter 2. Methods
Chapter 3. Results
Chapter 4. Discussion
Appendix. Sleep questionnaire
THE EFFECTS OF EXTENDED BED REST ON HUMAN SLEEP PATTERNS
SCOTT S. CAMPBELL
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY
OF FLORIDA IN PARTIAL FULFILLMENT OF' THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA 1981
Scott S. Campbell
The author would like to thank the members of his supervisory committee for their assistance and criticism during the preparation of this dissertation. The author would especially like to express his deep appreciation to Dr. Wilse B. Webb whose encouragement, guidance, time, and patience provided a constant source of motivation and inspiratiOnr Thanks likewise go to Briggs, Lewis, Alton, and Gregg whose technical assistance and friendship were invaluable. And final thanks to my parents for their support, both moral and financial, without which the completion of this dissertation would have been impossible.
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................ ............ iii
ABSTRACT ........ ....................... ..vii
ONE INTRODUCTION ..... ................. l...
Sleep as a Biological Rhythm . ...... I
Uniphasic or Ultradian ? ..... .......... 4
TWO METHODS ........ ................. ..12
THREE RESULTS ......... .................... 15
Initial Sleep Period ............ .... 15
Bedrest Period ...................... ..17
Circadian Considerations ............ ...24
FOUR DISCUSSION ........ .................. 33
Total Sleep Time .................. 35
Uniphasic or Ultradian? ... .......... ..49
SLEEP QUESTIONNAIRE .... .............. ...53
REFERENCES ........ ....................... ...55
BIOGRAPHICAL SKETCH ..... .................. ..60
LIST OF TABLES
I Comparisons of sleep stage characteristics for 1
baseline (Night 2), bedrest period, and normative group.
II Individual and group statistics for the bedrest 20
III Distribution of bedrest sleep periods by the 21
presence or absence of REM and Stage 4 sleep.
IV Comparison of sleep variables as a function of 25
night (11 PM 7 AM) and day (7 AM 11 11M).
V Sleep onset times of longest sleep episodes for 28
Night 2 (baseline), 3, and 4.
VI Comparison of sleep variables between first and 31
second 24 hours of bedrest period.
LIST OF FIGURES
1 Placement of sleep/waking episode across 60 18
hours for individuals and group.
2 Example of sleep across BP (#932). 19
3 Total number Of subjects asleep, for each hour 26
across the bedrest period.
4. Proportions of TST spent in REM sleep, as a 29
function of time of day.
Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
THE EFFECTS OF EXTENDED BED REST ON HUMAN SLEEP PATTERNS
Scott S. Campbell
Chairman: Wilse B. Webb
Major Department: Department of Psychology
That the sleep response is one of numerous physiological functions which may be classified as a biological rhythm is well-established. Less well-founded, despite its popularity, is the notion that the
sleep of adult humans maintains an inherent tendency to occur monophasically within each 24 hours, typically during the nocturnal portion of the 24-hour day.
This dissertation addresses the hypothesis that self-imposed and/ or sociophysically mediated behavioral controls have a significant
influence on the manifestation of such a uniphasic sleep pattern,, and that attenuation of behavioral controls may result in a "loosening"s of the circadian framework of typical adult sleep.
Each of 9 young adults was electrographically recorded over a
period of 60 hours, during which behavior was restricted primarily -to lying quitely in bed; i.e.,' subjects were not permitted to read, write, vii
listen to music, watch TV, exercise, etc. Meals were served at random intervals, and subjects had no knowledge of time of day throughout the bedrest period (BP).
The data indicate that a reducton in behavioral controls, which typically influence the sleep process, results in substantial alterations in the placement and periodicity of sleep. Sleep episodes became
evenly dispersed across the 24-hour day, resulting in an approximate 6 hour sleep/waking cycle.
While the average sleep period duration decreased, mean total
sleep time for the bedrest period (28 h) exceeded, by more than 40%, that which would be expected under the assumption of a uniphasic sleep! waking rhythm. The continued tendency toward a nocturnal weighting of total sleep was clear, however, since 55% of TST for BP occurred during the night (11PM to 7AM).
Within sleep structure (e.g., sleep stage percentages, mode of
appearance) was affected only slightly by the looseningn" of the sleep response. REM sleep retained its tendency to occur differentially across the 24-hour day; stage 4 sleep appeared -to maintain its relationship to prior wakefulness.
It is suggested that the sleep/waking patterns observed in this
study may be further manifestations of an inborn (albeit, highly. dampened) ultradian sleep/waking rhythm.
Slee AsaBiological Rhythm. That the sleep response is one of a vast array of physiological functions which maintain a reliable tendency to repeat at regular intervals has been demonstrated on numerous occasions over the past two decades (see for example., Aschoff, 1965; Richter, 1965; Symposia on Quantitative Biology, 1960; Webb, 1971; Webb and Agnew, 1974a). That the modulation of the sleep/waking cycle is controlled by innate and autonomous mechanisms seems, also, to have been well established.
In a free-running (time free) environment, subjects display the continuation of a sleep/waking rhythm which deviates slightly from the standard 24 hours (usually longer). The only plausible explanation for such a finding, according to Aschoff (1965, p. 1427) is
"that this rhythm is not imposed on the organism by the environment, but is truly endogenous. We are dealing with a self-sustaining oscillation which is free-running under constant conditions and has
its own inherent frequency."
The autonomous nature of the sleep/waking rhythm may also be demonstrated in the free-running environment, relative to other
rhythms. The vast majority of rhythms which are in phase with the sleep/waking cycle in the 24-hour environment become desynchronized upon introduction into the time free environment (Aschoff, 1978; Aschoff and Wever, 1976; Wever, 1973). An example of such
desynchronization is that which occurs between the temperature and sleep/waking rhythms. When both rhythms are entrained to 24 hours,
the maximum temperature typically occurs just prior to retiring, and the minimum temperature occurs toward the end of the sleep period. However, under free-running conditions, maxima and minima of rectal temperatures become independent of sleep onset and termination.
In addition, the sleep/waking rhythm may be entrained to artificial light/dark regimens while typically in-phase rhythms maintain their free-running periodicities. For example, throughout 10 days of entrainment to a 3 hour sleep/waking cycle, subjects' temperatures continued to exhibit characteristic circadian periodicities (Weitzman, Nogeire, Perlow, Fukushima, Sassin, McGregor, Gallagher, and
Hellman, 1974). Such data "contradict any hypothesis of a simple 'cause--and-effect' relationship between the activity-rest cycle and the rhythm of body temperature, and suggest a system of two coupled oscillations . with a mutual phase relationship which depends on the conditions" (Aschoff, 1978; p. 740).
Further evidence of the sleep/waking cycle's autonomy relative to other biological rhythms may be seen in the results of sleep deprivation studies. In the absence of sleep (for more than 70 hours) measures of performance, temperature and endocrine function all showed continuation of endogenous ciradian rhythms (Murry, Williams, and Lubin, 1958; Froberg, Karlsson, Levi, and Lidberg, 1975, as cited by Aschoff, 1978).
Examinations of the maturation of the human sleep/waking rhythm have also provided evidence for its innate and autonomous nature.
After observing the development of an initial 25-hour periodicity in an infant maintained on a self-demand sleep-wakefulness and feeding schedule, Kleitman and Engelmann (1953) concluded that "there may be a 'natural' rhythm which only has to be adjusted to the 24 hour alternation of night and day" (p. 280). Other researchers have also observed the development of adult-like, primarily monophasic, nocturnally placed sleep under similar conditions of self-demand feeding (Parmelee, Wenner, and Schulz, 1964; Salzarulo, Fagioli,
Salomon, Ricour, Raimbault, Ambrosi, Cicchi, Duhamel, and Rigoard, 1900).
While the sleep/waking rhythm clearly appears to be inborn and independently regulated, it may, at the same time be entrained by exogenous Zeitgebers, to frequencies other than those characteristic of the free-running environment. It has been demonstrated that
human subjects are capable of maintaining sleep/waking cycles of various lengths, quite efficiently within a range of about 20 to 27 hours, as the result of entrainment to appropriate light/darkregimens. It has been further shown that the sleep/waking rhythm characteristic of a free-running environment may be regulated by "rigid control of
the sleep portion of the cycle particularly of the wakeup time" (Webb and Agnew, 1974b; p. 701).
Several investigators also point to the developmental literature
as a source of evidence for the entrainability of the sleep/waking rhythm (Ellingson, 1975; Gesell and Armatruda, 1945; Kleitman, 1963; Sander, Stechler, Burns, and Julia, 1970; Sterman, 1979). As expressed by Sterman (p. 213), "the development of sleep is a postnatal
phenomenon, subject both to the dictates of physiological maturation and the influences of environment. Such factors as geography and social custom entrain the physiological substrates of the sleep -waking cycle to determine the behavioral patterns which will come to characterize these states in a given culture."
Indeed, the very fact that adult humans maintain a 24-hour
sleep/waking periodicity, in spite of an inherent rhythm with a frequency longe' than 24 hours, is clear evidence of the entrainability of the rhythm.
It appears then, that the oscillation between sleep and wakefulness, characteristic of adult human subjects, meets the criteria necessary for its designation as a biological rhythm. Sleep is an inborn, independently regulated, exogenously entrainable, regularly occurring response.
Up phasic or Ultradian? While sleep and wakefulness clearly
comprise a physiological system which may be classified as a biological rhythm, determination of the rhythm's inherent periodicity remains less clear, since few studies have been conducted which adequately address this point. It is generally assumed that the sleep/waking cycle is anuniphasic one. In addition to the obvious support for such a notion, i.e., that adult humans typically obtain sleep in a single, nocturnal block, results from studies in which the normal sleep period has been dispersed or eliminated have also been cited as evidence for this view. In such experiments, performance measures are usually lowest and subjective reports of sleepiness are
usually greatest during the interval in which the subject would normal ly be sl eepi ng (Coiquhoun, 1971; Wei tzman et al. 1974).
It has further been reported (Weitziman et al., 1974) that "a
striking persistence of a circadian pattern of total sleep time" (p. 1020) was exhibited throughout 10 days of entrainment to a 3-hour day. In this study, subjects were encouraged to sleep 1 hour out of each 3 hours. The authors reported that the 4 sleep periods beginning at 3 AM, 6 AM,. 9 AM, and noonaccounted for 70% of the total sleep time.
The decreased sleep efficiency associated with dispersed and
displaced sleep schedules has also been seen as lending support to
the notion of an inborn, nocturnally placed, uniphasic system of sleep and wakefulness. Studies in which the normal, nocturnal sleep period has been shifted to a time typically employed for work or other waking activities, indicate that such sleep episodes are characterized by significantly greater proportions of wakefulness (stage 0) after initial sleep onset, as compared to baseline (normal) sleep (Webb, Agnew, and Williams, 1971). Such findings suggest that the maintenance of sleep is more difficult when the sleep period is shifted from its typical, nocturnal placement. Further, as experimentally circumscribed 'days' deviate from the normal 24 hours, sleep efficiency (amount of time in bed spent asleep), becomes less. Webb and Agnew (1975) found that Subjects maintaining 'a sleep/waking schedule of 3 hours sleep/6 hours wakefulness only achieved 80% sleep efficiency when compared to baseline conditions (8 hours sleep! 16 hours wakefulness). Weitzman et al. (1974) reported,56% sleep
efficiency for subjects attempting a 3-hour cycle compared with 90% efficiency for the baseline condition.
It has also been noted in dispersed, as well as displaced sleep, that the intrasleep structure of the "new" episodes differs in several details from that seen in normally occurring nocturnal sleep. For
example, Weitzman et al. (1974) observed "early" REM periods (preceded by less than 10 minutes stage 2 at sleep onset) and "sleep onset" REM periods (preceded only by wakefulness or stage 1) in over half of all REM episodes recorded over the 10 days of 3-hour sleep/wake scheduling. Results of the displacement of subjects' typically nocturnal sleep into day sleep include significant increases in the amount of stage I and reductions in the amounts of stages 3 and 4 (Webb and Agnew, 1978). Such findings lend further support to the view that these sleep episodes differ substantially from endogenously modulated sleep periods.
It may be argued, however, that studies of sleep dispersion and and displacement do not adequately address the question of the inherent frequency of the sleep/waking cycle. Rather, such studies more specifically test the entrainability of the presumed uniphasic rhythm. Failure to effectively impose a shortened regimen upon a hypothesized uniphasic rhythm does not necessarily rule out the existence of an ultradian sleep/waking rhythm. Yet, data supporting such a possibility are not extensive.
One type of evidence used to support the suggestion that the
human sleep/waking rhythm is inherently ultradian is provided by the analysis of sleep patterns of individuals participating in Polar expeditions. Lewis (1961; Lewis and Masterton, 1957) has suggested
that given a situation in which adherence to customary circadian scheduling is less stringently controlled, a more accurate reflection of the inborn sleep/waking rhythm may emerge.
In the Polar regions the photoperiod is not diurnal, but seasonal. Further, expeditions into these regions typically maintain little resemblance to an organized community, in that there are few circumscribed daily routines, no specific feeding schedules, few timetables (Lewis, 1961). Sleep records from 5 Polar campaigns suggest that the organization of sleep/waking patterns was a direct function of the stringency with which the "community" was structured. For example, members of the British North Greenland Expedition (1952-54) were allowed to sleep as long as they liked, at virtually any time they had the inclination to do so. Under such conditions, sleep durations per 24 hours did not increase substantially over baseline amounts. Yet, the length and placement of individual sleep episodes showed considerable deviations from members' normal sleep habits recorded in England. The tendency toward polyphasic sleep placement was most extreme during the three months of continuous light or darkness. "During these periods .. men used any of the 24 clock-hours for sleep, The winter months were characterized by many interruptions to sleep and by the taking of naps" (Lewis, 1961, p. 325). Although no data were presented relative to the rhythmicity of these multiple sleep episodes, it appears that the uniphasic "nature" of the sleep
process loosened somewhat under conditions of limited environmental cues and negligible behavioral and cultural restraints.
Within the more structured hours of daily life, it has been
suggested that the ultradian nature of sleep and wakefulness may be manifest in the form of naps (Webb, 1978). Webb's proposal that naps are part of an inborn sleep/waking rhythm is based on the contention that certain characteristics of these intermittant sleep episodes
match features which are common to biological rhythms in general. Specifically, it is maintained that naps are: 1) temporally, repetitive, 2) species specific, 3) often developmental, 4) innate and unlearned, 5) endogenous, and 6) adaptive. While evidence seems to support the first four characteristics, and only post hoc speculation can address the sixth, Webb points out that experimental support for the claim that naps are endogenously mediated is extremely limited, and that further data are "likely to be slow forthcoming." This is due primarily to the fact that virtually all procedures utilized for the examination of presumed biological rhythms have prohibited other-than-circumscribed sleep episodes as a consequence of experimental design considerations. Such experiments typically focus on the interactions of major components of sleep, waking and performance. As such, "the very nature of naps in these designs are uncontrolled and interfering sources of experimental variance" (Webb, 1978 p. 316). Two primary designs of this type are the free-running and bedrest procedures.
It has been noted that the sleep/waking rhythms maintained by subjects in free-running environments provide excellent support for the notion that such rhythms are innately and independently controlled. Under such conditions, time cues are removed from the
environment, but other behavioral controls are typically left Unaltered. That is, subjects are askIed to lead a "normal" life, including eating three meals a day in normal sequence, having the opportunity for exercise and other activities such as reading, writing, watching TV, etc., arid maintaining circumscribed sleep schedules (no naps). As a result, these subjects have a tendency to carry on day-to-day life in a manner to which they have grown accustomed over the years. Clearly, such circumstances may strongly bias behavior toward a circadian schedule, perhaps entraining an inherently ultradian rhythm -to an environmentally and culturally modul ated ci rcadilain frainewoirk. These factors notwi thstandi ng, the sleep patterns displayed by subjects in time -Free environments have been seen as providing evidence not only for the biological basis of the sleep/waking rhythm, but for -its circadian (uniphasic) nature, as well.
The latter inference seems tenuous, at best. For', when controls on -the number and placement of sleep episodes are reduced in freerunning environments, evidence seems to indicate that the "normal sleep pattern" (single sleep period of from 7 to 10 hours with occasional napping) is modified. Webb and Agnew ('1974a) reported that under such circumstances "a significant increase-in both long and short periods of sleep, compared to -the 24-hour environment" (p. 620) resulted. While neither the placement nor the periodicity of the increased episodes was analyzed, the authors concluded that such changes in the sleep response showed the extent to which the uniphasic sleep pattern is'disrupted by reduced controls on sleep p1 acement.
While studies employing a bedrest design may clearly eliminate some behavioral controls left in tact by the free-running design (most notably physical exercise), this procedure is also typically
characterized by experimentally circumscribed sleep periods as a consequence of full schedules of psychological, psychophysiological and performance testing (see for example, Ryback & Lewis, 1971; Ryback, Lewis & Lessard, 1971).
One recently published study (Nakagawa, 1980) however, does
provide some insight into sleep/waking cycles in the absence of cultural mediation and behavioral controls. In this study, subjects were required to remain lying quietly in bed for 10 to 12 hours immediately following a full night's sleep. The original aim of the study was to "elucidate changes in daytime states of consciousness" by observing "the EEG patterns of (awake) subjects in restrained postures under minimally changing experimental conditions" (p. 524).
Despite explicit instructions to remain awake during the 10 to 12 hour period, howeVer, Subjects experienced "an uncontrollable
desire to fall asleep," resulting in sleep/waking cycles of approximately 4 hours across the experimental period. Again, it appears that the uniphasic placement of the sleep process loosened in response to a reduction in behavioral controls.
In summary, most designs employed in the investigations of
the human sleep/waking rhythm are inadequate for that purpose since they include strict controls over waking and sleeping as a necessary part of the procedure. However, results from studies in which such controls are relaxed indicate that subjects have a tendency to
relinquish their typical uniphasic sleep placement in favor of a more dispersed, polyphasic sleep system.
The present study attempted to address the hypothesis that
behavioral, cultural and environmental factors serve to entrain an inherently ultradian sleep/waking rhythm to a uniphasic, 24-hour framework by imposing upon the organism a series of behavioral controls. In the experimental environment, such controls are frequently mimicked by circumscribed sleep/waking schedules, feeding regimens and testing procedures. These external controls "may create incompatible responses which suppress the expression of (the) rhythmic response or create such a 'noise' background as to not permit measurement" of the hypothesized ultradian rhythm (Webb, 1978 p. 315). Therefore, byminimizing "incompatible responses" and "noise background" the present study sought to "emancipate" the hypothesized ultradian rhythm from control by a self-imposed and/or sociophysically mediated circadian framework. By so doing, it was proposed that the presence of such a rhythm may be more readily observed and measured. Specifically, subjects were required to maintain relatively static, basal levels of behavior over a period of almost three days, during which time their sleep/waking behavior was the primary
variable of interest.
*rhe subjects for this study were 10 young adults (5 males and 5 females) ranging in age from 18 to 25 years (mean = 20.4). Subjects were selected after questionnaire (Appendix 1) responses revealed normal sleep patterns and the absence of chronic health problems and/or acute illness.
Each subject slept for 2 nights in the laboratory immediately prior to the beginning of 60 consecutive hours of bedrest. Between
the 2 nights in the laboratory subjects were permitted to maintain their normal daily schedules with the stipulation that no naps be taken and no drugs (including alcohol and caffeine) be ingested during that period.
For each session, 2 subjects reported to the laboratory approximately 1 hours prior to their normal bedtimes (about 11 PM) for electrode placement. Five millimeter gold disc electordes were applied over Cambridge electrode jelly and held in place by coilodian saturated gauze strips. EEG and electrooculogram (EOG) were continuously monitored for each subject using a Grass Model VI electrophysiograph. The EEG of each subject was recorded on three channels between electrode sites Fpl F7, P1 T5, and C3 A2. The EG was monitored on a separate channel by electrodes placed on the external canthus of each eye.
At the completion of electrode placement each subject retired to a private, electrically shielded, sound attenuated, temperature controlled room. Each subject's record was scored in one-minute epochs, following the methods described by Agnew and Webb (1972a). Cross-scoring of random 2-3 hour segments of the sleep portions of each record revealed a between-scorer reliability of greater than 90%.
Sleep onset was determined by the appearance of the first spindle or K-complex (Agnew & Webb, 1972b). A sleep period was considered as Such when sleep continued, uninterrupted by more than
20 minutes of wakefulness, ,or at least 30 minutes. A waking period was defined as Stage 0 EEG for at least 20 minutes.
Timing of the 60 hours of bedrest began with the spontaneous awakening of each subject from his/her second night of laboratory sleep and the subject's verbal report that he or she felt rested and had had enough sleep. At this time subjects were given an opportunity to eat breakfast and use the bathroom. No intentional time cues were given the subjects upon awakening nor at any other time 'throughout the bedrest period, with the exception that each subject was told when hie or she was "past the halfway point" at a random time after 30 hours had past. However, uncontrollable, general time cues from exogenous sources (eg. nearby building construction, general building noise during working hours, homecoming festivities during one session subjectss 945 & 946)) were present in varying degrees from session to session.
During the 60 hours of bedrest, subjects were allowed minimal
exogenous stimulation. Activities such as reading, writing, listening
to music or watching television were prohibited. Conversationsduring the period were limited to brief dialogues with the experirienter at meal -times. No instructions were given relative to when or when not to sleep. Subjects were asked to lie as quietly as possible, but were permitted to change positions in bed when inclined to do so. Closed circuit TV monitors were employed to insure adherence to the experimental instructions. Subjects were permitted to go to the bathroom (in room) at their convenience and were allowed to sit up iii bed during meals.
Meals were served unsystematically (always during an ongoing waking period, as determined by the EEG) and consisted oi a choice of several types of sandwiches, vegetable dishes, desserts and noncaffeinated beverages. A maximum of I- hour was permitted for the completion of each meal. Several types of fruit and a pitcher of ice water were also available to each subject ad libitum.
Illumination in each room was provided by a 60 watt lamp placed on a table by the subject's bed, and control of light and control of light and darkness was at the discretion of each subject.
One of tChe 10 subjects terminated participation prior to the end of the bedrest period. Since only 12 hours of bedrest were re.corded for this subject, the results presented here are those of the
9 subjects who completed the session.
The criterion used here to define a "sleep period" (.i.e., 30 minutes of sleep, uninterrupted, by more than 20 minutes of wakefulness) accounted for 91.3% of all sleep recorded. Eight sleep episodes had durations of less than 30 minutes (mean = 7.25 min., range =2 to 18 mn.), and therefore were not considered "sleep periods" in the following analyses.
Initial SieeD Period. The mean total sleep time (TST) for the sleep period immediately preceding the onset of the bedrest period (Night 2), was 8.72 hours, with a range of from 5.82 hours to 10.43 hours. Sleep stage percentages for the period were generally within normal limits. However, as shown in Table 1, there was a significantly greater proportion of Stage 0, t (df =39) =2,32, p.<05 (all
levels of significance are based on a two-tailed test), and a smaller percentage of stage 1, t(39) = 5.04, p.,001, and stage 3, t(39) =2.20, p.<05, in this sample as compar-ed with a normative
group of 16 males and 16 females of approximately the same age (mean= 24 years) previously recorded in the same laboratory (Williams, Agnew
and Webb, 1964; 1966). "Chopping" each record to an artifical maximum 15
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detail, the sequencing of sleep and wakefulness of one subject (932) across the bedrest period. Individual and group statistics for the entire bedrest period are presented in Table II. BP was characterized by an alternation of waking periods with an average length of 2.7 hours (range =.4 to 10.2 hours) and 'Sleep periods with a mean duration of 2.99 hours (range =.5 to 11.6 hours). Subjects spent almost half of BP asleep (47.6%) with a mean total sleep time of 28 hours (range =20 to 37.3 hours), Sleep was dispersed across an average of 9.3 episodes during the bedrest period (.range = S to 13).
These results are in contrast to what would be expected under the assumption of a uniphasic model of sleep. Under such an aSSuffip tiori, one would predict 2 discrete sleep episodes across the 60 hours, placed within the normal nocturnal periods (approximately 11 PM to
7 AM), with a mean TST for the bedrest period of about 16 hours (about 27% of BP).
Sleep periods during BP could be divided into four general
categories based on the presence or absence of stage 4 and REM sleep, as shown in Table TIT. Seventy percent (59) of all sleep periods recorded over the bedrest period were 'full blown' sleep episodes, in that all stages of sleep were observed. Of the remaining 25 sleep periods, 3 (all day episodes) showed neither REM nor stage 4 sleep. Nine sleep periods (8 days, 1 night) exhibited an absence of REM sleep and 13.(12 days, 1 night) showed no stage 4 sleep.
The mean period length of those episodes with neither REM nor stage 4 was 61 minutes. The mean duration of 'noREM' sleep periods was 65 minutes, and the 'noStg4' sleep episodes averaged 84 minutes
duration. This is compared to a mean duration of 225 minutes (.3.75 h) 'for those sleep episodes which contained both stage 4 and REM.
The occurrence of these events in terms of sidereal time was also examined, The three periods containing no REM and no stage 4 occurred after noon and before the onset of the night phase (11 PM/). All but 2 of the 'noREM' periods occurred between 2 PM and 10 PM. The 'noStg4' episodes occurred across the entire day phase (7 AM to 11 PM) with only one such episode occurring at 'night' (6:40 AM).
Regarding the mode of appearance of REM sleep episodes, of 153 REM periods recorded over BP, only 3 were characterized by onsets at: the beginning of a sleep period. Sleep onset REM periods (SOREMPS) were defined as those REM episodes occurring at the onset of sleep which were not preceded by more than 1 minute of stage 2. Two sleep episodes containing SOREMPS also were characterized by the absence of stage 4 sleep. The SOREMPS were contributed by 3 subjects, had a mean duration of 15.3 minutes (9, 10, and 27 minutes), and occurred at approximately 6:30 AM, 6:30 PM, and 1:30 PM, respectively.
In an effort to further elucidate the factors involved in the cycling of REM sleep, two examinations were made. In the first procedure, the REM sleep cycle (defined as the interval between the onset of one REM period and the onset of the next) was calculated for each subject's baseline night (Night 2). The onset points of the cycle were then superimposed across each subject's entire bedrest period (including waking episodes) -to test the hypothesis that the REM cycle was independent of pri.or sleep time. Also, the cycle was
superimposed across each subject's compressed bedrest period, in which waking intervals were removed to obtain a continuous sleep period, to test the possible sleep dependency of the REM sleep cycle. The initial onset of the superimposed cycle corresponded to the onset of the last REM sleep period of Night 2.
The relationship between the superimposed REM cycle and the occurrence of actual REM episodes was examined by calculating the mean difference between each onset point of the hypothesized cycle and W, closest REM epoch within that sleep period. The average difference between each onset of the superimposed cycle and the appearance of an actual REM epoch, across the intact bedrest period, was 15.8 minutes CSD = 3.7 min). The mean difference between the values for the 'compressed' BP was 14.5 minutes (SD 4.7 min). The difference between the two conditions was not significant.
To further test the sleep dependency of the cycle, the mean REM cycle length of the 'compressed" BP, for the group, was determined. Again, beginning the cycle with the onset of the last REM period of Night 2, mean cycle length for the 'compr essed' BP was 96.84 minutes WD = 10.42 min). This is compared with a-mean REM cycle length of 96,56 minutes (SD = 12.76 min) for Night 2.
Circadian Considerations. There were considerable differences in several measures as a function of time of day. For comparative purposes, waking and sleep periods were considered daytime events if they were initiated between 7 AM and 11 PM. "Nighttime events were defined as those episodes with onsets between 11 PM and 7 AM.
TARLE IV, Comparison of sleep variables as a function of night
(11 PM 7 AM) and day (7 AM 11 PM).
Overall Night Day
Mean TST 27,99 h 15,34 h 12,65 h
(5.39) (3.30) (4.91)
Mean Sleep 2.99 h 5.52 h 1.93 h
Period Length (2.35) (2.65) (.98)
Total # Sleep 84 25 59
Sleep/Wake 6.10 h 7.81 h 5.25 h
Cycle Length (2.68) (3.26) (1.74)
% Stage 0 3.59 3.50 3.64
(2.28) (2.26) (3.58)
% Stage 3.28 3.88 2.81
(1.87) (2-79) (2.06)
% Stage 2 58,41 56.37 60.80
(4.94) (5.76) (6.22)
% Stage 3 4.33 4.13 4.94
(1.24) (1.58) (1.7S)
% Stage 4 9.86 8.89 11.01
(4.54) (5.37) (4.28)
% Stage REM 20.47 23.13 17.54
(2.94) (4.01) (3.87)
Mean p <.001 t test, two-tailed
(SD) p < .01
CL (4- )
Of 84. total sleep episodes recorded for the group across the bedrest period, 59 (70.2%) occurred during the day and 25 (29.8%) occurred at night, However, over half of the total sleep time (54.7%) during BP was obtained during episodes initiated between 11 PM and 7 AM.
Comparisons between day sleep periods (DS) and night sleep periods (NS) of' temporal measures and sleep stage percentages are shown in Table IV, The most notable difference in measures of DS and NS was with regard to mean sleep period duration. NS episodes continued for a mean duration 5,52 hours (SD = 2.65 h) compared to an average length of 1.93 hours (SD = .98 h) for sleep episodes initiated during the day (t (82) = 6.58, p<.001). Conversely, the mean duration of waking episodes was 1.47 hours (SD = 1.04 h) for nighttime events and 3.12 hours (SD = 2.4 h) for those initiated during the day (t (82) = 4.29, p4.001). Consequently, the sleep/ waking cycle length (defined as the interval between the onset of one sleep episode and the onset of the next) increased significantly from day (5.25 h, SO = 1.74) to night (7.81 h, SD = 3,26) t (73)
Figure 3 presents, by hours, the number of subjects sleeping. across the bedrest period. The group tendency toward nocturnal sleep placement is evident. Of 144 total subject-hours available for sleep during the 2 night periods (11 PM to 7'AM), 104 (72.31/0) were used for that purpose. In contrast, of the 279"subject hours comprising the first and second day periods (.8 AM to 11 PM.and 7 AM to 11 PM) less than half 05.2%). were spent sleeping.
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The possible presence of a free-running sleep/wake rhythm was,
examined by comparing the mean sleep onset time of Night 2 (baseline) and the mean onset times of the longest sleep periods of Nights 3 and 4. Thle mean sleep onset times for the group exhibited a tendency to, occur later on each succeeding night--slightly under 1 hour later, on Night 3 (as compared to baseline) and 42 mliffutes later onl Night
4 (as compared to Night 3). However, as shown in Table V only 2 subjects (929 and 937) demonstrated consistent free-running patterns across the three nights. Four additional subjects delayed the onset of' their major nocturnal sleep onset on Night 4 (relative to Night 3).
Sleep stage percentages were not affected substantially as a function of time of day, While there was slightly less stage 1 (21.8 vs 3.9%) and slightly more stage 2 (60.8 vs 56..4%) and stage 4 (11 vs 8.9%) during the daytime sleep periods, only the difference in REM sleep percent was significant, with REM sleep comprising just over 23% of NS episodes and only 17.5% of DS periods (t (82) =5.91, p<.001). The difference in REM percent appeared to be a consequence not only of the difference in sleep period length but also of the maintenance of a circadian pattern of REVS across the the bedrest period, as shown in Figure 4. The largest proportion of 1ST spent in REM sleep occurred during those sleep episodes initiated between 4 AM and 8 AM. The proportion of REM sleep decreased across thle-next three 4-hour time blocks until reaching a low of 11.57% of TST for sleep episodes initiated between 4 PM and 8 PM. The percentage of REM sleep then exhibited a steady increase across the subsequent 4-hour time blocks (8 PM to 12 MID and 12 M to 4 AM).
TABLE V!, -Comparison of sleep variables, between first andI second 24
hours of badrent period.,
Overall 1st 24 [IRS 2nd 24 [IRS
Mean TST 27,99 h 14.46 h ** 10.97 h
(5.39) (2.28) (2,36)
Mean Sleep 2.99 h 3.54 2.82 h
Period Length (2.35) (1.92) (1.44)
Total # Sleep 84 39 33
Sleep/Wake 6.10 h 5.19 h 5,64 h
Cycle Length (2.68) (220) (2.04)
% Stage 0 3.59 2.94 4.48
(2.28) (2.23) (4.25)
% Stage 1 3.28 3.03 3.74
(1,87) (1,93) (2.66)
% Stage 2 58.41 .59.69 56.68
(4.94) (4.03) (8.50)
% Stage 3 4.33 4.15 4.66
(1.24) (1.40) (1.58)
% Stage 4 9.86 8.39 11.39
(4.54) (3.60) (6.88)
% Stage REM 20.47 21.77 19.02
(2.94) (2.56) (4.82)
Mean **p< .01
(SD) t test, two-tailed
In addition to day/night differences, there was alsho disparity in temporal measures as a function of elapsed time within the bedrest period. Table VI compares rsT, sleep period duration, sleep/waking cycle length, and sleep stage percentages recorded during the first 24 hours of bedrest with those recorded during the second 24 hours. Total sleep time 'for the first 24, hours (14.5 h) was significantly longer than TST for the second 24 hours (10.9 h) (t (16) =3.19, p< .01). While the decrease in TST was,, in part attributabl e to a reduction in the total number of sleep episodes during the second 24 hours (39 vs 33), a decline in the mean sleep period length across BP (3.54 h vs 2.82 h) also contributed to the difference.
Despite the decrease in overall sleep period duration, the
sleep/waking cycle length remained essentially unchanged throughout the bedrest period. For purposes of comparison, only those sleep/ waking cycles initiated and completed within one or the other 24 hour periods were considered. The mean duration of sleep/waking cycles occurring during the first 24 hours was 5.2 hours (SD = 2.1 h), while the mean cycle length of those completed during the second 24 hours was 5.6 hours ('SD =2.4 h).
There were no significant differences in sleep stage proportions between the 24-hour intervals. However, trends were observed relative to stages 4 and REM. Stage 4 increased (from 8.4. to 11.4%) from the first 24 hours to the next; this despite the fact that there were more sleep episodes containing stage 4 in the first 24 hours (32 vs 27). Conversely, REM sleep decreased by over 10% from the first to the second 24 hours..
The results of this study substantiate and further detail previous reports that a reduction in the control of the sleep response results in a 'loosening' of the uniphasic, nocturnally placed sleep pattern typically observed in adult humans. At t"he same time, however, the results underscore the tendency of sleep to be differentially weighted toward a definite and persistent nocturnal placem,.ent.
On the one hand, the data suggest a quadriphasic sleep pattern, with the onset of sleep episodes occurring at approximately 6 hour intervals throughout the bedrest period. While such a rhythmicity proved to be highly variable within subjects, from -one sleep period to the next, the relatively small between-subjects variability emphasizes the regularity of such a rhythm within the group. That the number of sleep periods was proportionately placed, relative to day and night, further accentuates the uniform distribution of sleep episodes across the 24-hour day. The 'day' phase (7 AM to 11 PM) comprised approximately 73% of the total bedrest period. Correspondingly, 70% (59) of the total number of sleep episodes recorded- across BP were initiated during the day.
On the other hand, comparison of the mean duration of those day sleep periods with the average length of sleep periods initiated at night clearly illustrates the substantial orientation toward the 33
nocturnal placement of total sleep time. Over half (55%) of the total sleep time recorded during BP was obtained during sleep periods initiated between 11IPM and lAM, despite the fact that 'night' comprised only 27% of the total bedrest period.
These findings are in accord with those reported by Weitzman. et al. (1974) relative to the placement of the sleep of subjects maintained on a 3-hour 'day' In that study, the sleep of 7 subjects exhibited a strong tendency to occur, during the scheduled sleep periods beginning at SAM, 6AM, 9AM, and noon. While the authors note the shift away from typical sleep placement (i.e., 11PM 7AM) during the 10 days Of u]itradian Cycling, they emphasize th2 "highly resistant nature" of the circadian loading of the sleep response.
Webb and Agnew (1974a) also noted a tendency for subjects to
maintain a circadian, primarily nocturnal, placement of total sleep time in a free-running environment. The authors cite three aspects of their findings which suggest a continuation of "the entrained influence
of the original 24-hoiur cycle." First, several subjects showed sleep onset times during the first 3 or 4 days which were significantly earlier than would be predicted by a pure free-running hypothesis. Secondly, throughout the 14 days of the study, there were tendencies on the parts of 5 of the 7 subjects for sleep onset times to 'regress' periodically, thereby -increasing the probability that 'sleep onset would occur during the nocturnal phase (between midnight and 7AM). Finally, there were two occasions in which subjects skipped sleep periods, the predicted onsets of which would have occurred during the day phase (specifically, noon anid 4PM), and instead delayed initiation of the next sleep periods to nocturnal placements (11PM and 3AM, respectively).
The tendency toward a free-running sleep/waking cycle was not apparent in the present study. While the mean sleep onset times of
the major nocturnal sleep episodes became successively later across the three nights, only 2 individuals exhibited such a tendency. Other subjects delayed sleep onset on Night 3, only to advance onset time on Night 4. Still others exhibited a reverse trend. Such 'scalloping' of the expected free-running rhythm in the present study may reflect -the continued inclination of some subjects to maintain their sleep in its typical nocturnal placement.
Total Sleep ime. The results of the present study are also
consistent with previous findings relative to the amount of total sleep obtained. In summing up the findings on studies of unrestricted sleep, Webb and Agnew (1975a) noted that "it may now be stated with ccnf'idence that permitting subjects to sleep ad lib under conditions which have not increased the sleep need by prior deprivation or increased energy
expenditure will consistently result in increased sleep length," (p, 369). In addition, sleep logs maintained across several weeks reveal that average weekday ('restricted') sleep and weekend ('unrestricted') sleep differs by an hour or more (Johns, Gay, Goodyear, and Masterton, 1971; Webb, 1981; White, 1975).
The subjects in the present study were instructed,' on Night 2, to sleep until -they felt well-rested and no longer sleepy. The mean sleep
duration for Nigrit 2 (8.7 hrs) was within minutes of the mean total sleep time (8.8 hrs) reported for 4 subjects (10 nights each) permitted to sleep as long as they wished, following 10 nights of 'restricted' sleep which averaged 7.4 hrs per night (W4ebb and Agnew,
1974a) The mean sleep length for Night 2 is also in agreement with self-reported extensions in weekend sleep lengths (about 8.5 hrs).
The mean total sleep time reported here is, however, almost an
hour less than that of young adults (9.6 hirs) studied by Verdone (1968) and Webb and Agnew (1975a). It seems likely that the mean total sleep time for Night 2, like typically reported weekend sleep, was a consequence of the relaxation of self-imposed controls on sleep length (e.g., alarm clocks), rather than an expression of the complete satisfaction of sleep 'need'. Several subjects in the present study were rather impatient to terminate Night 2 and to initiate the bedrest period. This is illustrated by the case of one subject who reported,
during a brief (3 mim) awakening, that she felt rested and had "'had enough sleep." The report came after approximately 2 hours had elapsed in Night 2. Clearly, such eagerness to 'get on with it' may have resulted in the termination of sleep prior to the spontaneous ending of
sleep due to satiety.
A more accurate measure of maximum sleep length may be derived
from the examination, across the bedrest period, of sleep durations per 24 hours. Beginning with the termination of Night 2 (typically around 8AM) the first.24-hour period was characterized by an average of 14.5 hours of sleep, the second 24 hours contained an average of almost 11 hours of sleep. Such figures are consistent with previously reported 24-hour sleep amounts. For example, Aserinsky (1969) instructed subjects to "make every attempt to sleep" while confined to bed for 30 hours (interrupted only twice for meals). During the first 24 hours (midnight to midnight) subjects obtained an average of*14.4 hours of sleep. During the 24-hour period beginning at 7:30AM, after a full
night's sleep (mean =7.04 hrs.), the mean sleep duration was 12.93 hrs. This figure is in remarkable agreement with the average TST for each of the first 2 24-hour periods, subsequent to Night 2, in the present study (12.71 hrs.). In light of such findings, it appears that 12 to 13 hours of sleep per 24 hours may be considered a close approximation of the maximum capacity for sleep (Aserinsky, 1969). However, at 'least three lines of evidence suggest -that substantially shorter sleep times may represent the maximum point of sleep 'need'. First, it has been proposed that REM density may be a reflection of "satisfaction of a sleep need, or . the buildup of a pressure to awaken" (Aserinsky, 1969, p. 155). It was found in that study that REM density reached maximum values after 7.5 to 10 hours of sleep. Secondly, under coniditions of perceptual deprivation, subjects averaged about 12 hours of sleep during the first 24 hours, but subsequently reduced sleep lengths until they approached baseline levels (about 7.5 hirs.) by the third or fourth day of deprivation (Potter and Heron, 1972)-~ Also in the present study, total sleep time during the second 24 hours of bedrest decreased. almost 25% when compared with that of the first 24 hours. It might be speculated that the decline would have continued, if bedrest had continued.
Nevertheless, with the exception of the perceptual deprivation study cited above, all values of sleep satiation or fulfillment of sleep "need" substantialy exceed the 7- to 3-hour sleep durations typically reported for normal young adults. The interpretation of such findings may be generally separated into two opposing views. It has been suggested, on the one hand, that the extended sleep observed in unrestricted sleep regimens is a consequence of decreased sensory input (see for example, Nakagawa, 1980; Heron, 1957). Proponents of
this view have speculated that an important -function of the sensory and perceptual systems is to maintain a waking level of arousal in, the reticular activating system. In studies comparable to the present one, where conditions are maintained at a relatively constant level, and
sensory stimulation is not only static but also depressed relative to normal levels, input from peripheral afferent pathways may be insufficient -to furnish the appropriate level of RAS activation. "In general, appropriate sensory stimulation is needed to maintain an arousal state in animals, but repetitive monotonous stimulation habituates the arousal reaction "(Nakaguawa, 1980, p. 532). In short the, according to
this view, extended sleep is the result of neurological "boredom" and/or habituation. Implied in such a view is the notion that the extended sleep time observed under unrestricted or bedrest conditions is not
representative of natural sleep tendency (or requii~ement), but rather, is simply one consequence of the organism's decreased requirement to process environmental stimuli and respond accordingly (Heron, 1957).
This is analagous to Flanigan's (1971) suggestion that the extended sleep observed in nonhuman subjects maintained under con-trolled and highly -favorable conditions (i.e., limited activity, plenty of food, no
predators) may reflect the upper limits of sleep that are organismically possible, rather than that which is typical in the animal 's natural habitats.
In contrast, it has been Suggested (see for example Webb and Agnew, 1975a) that the extended sleep lengths characteristic of unrestricted sleep conditions are, in fact, "normal" and that typically reported sleep durations of 7 to 8 hours may actually be the product of chronic sleep deprivation. In support of such a notion is the finding that
only one third of a group of individuals who completed 6-month sleep diaries reported that they usually awakened spontaneously in the morning. Further, half of the respondents in the study reported that they
were typically not well-rested upon awakening (Kleitman, Mullin, Cooperman, and Titelbaum, 1937). The extension of sleep on weekends reported
by most individuals also suggests a 'need' for more than the typically obtained weekday mean, Further, it has been shown that after 3 consecutive nights of sleep, restricted to a period between 11PM and 7AM (mean = 7.5 hrs), subjects slept an average of 2 hours longer on the 4th night when allowed to awaken spontaneously (Webb and Agnew, 1975a). The subjects in that study were not encouraged to extend sleep; indeed, they were "unaware that they would be allowed to sleep longer."
Similarly, the subjects in the present study were given no in-structions relative to the maintenance of sleep and wakefulness during the bedrest period, yet they also obtained substantially more sleep than self-reported normal sleep durations. This seems to be suggestive of an inclination toward, if not an actual 'need' for, more sleep than is typically obtained. Of interest is the observation that the extended
sleep durations resulted not from a lengthening of sleep episodes initiated at night, but rather from the addition of day sleep periods.
Nocturnal sleep (11PM to 7AM) per 24 hours did not exceed normal night sleep (7.8 h). However, day sleep episodes contributed an average of approximately 5 hours to each 24-hour total. It might be speculated
that the usual sacrifice of such day sleep periods is the source of our chronic sleep deprivation. On the other hand, the bedrest environment
in the present study was highly monotonous, with novel sensory input severely curtailed. It is, therefore, likely that such conditions
contributed somewhat to the observed tendency for extended sleep times, as-well.
Intrasleep Structure. The mean sleep stage proportions of the
combined sleep periods during BP did not differ significantly from those of the baseline night (Night 2), and were within normal limits reported for young adult populations, although REM and slow wave sleep (SWS) were significantly reduced when compared to the normative sample used here.
Such findings are in agreement with those reported by Webb and Agnew (1977) relative to the distribution of sleep stages in experimentally controlled, polyphasic sleep regimens. That is, despite influences -from changes in sleep length, p-1ior wakefulness and sleep onset times associated with various schedules of dispersed sleep, "when the total sleep obtained during these altered regimens is compared with baseline sleep on a 24-hour regimen, the basic structure of sleep persists" (p. 448).
Also, in accord with previous reports of dispersed and nap sleep (Maron, Rechtschaffen and Wolpert, 1954; Moses, Hord, Lubin, Johnson, and Naitoh, 1975; Nakagawa, 1980; Webb and Agnew, 1977; Weitzman et al. 1974) the occurrence of REM sleep maintained a circadian pattern across the bedrest period. Sixty percent of total REM time occurred during sleep episodes initiated between 11PM and 7AM. Further, while only 9 of the 84 sleep periods recorded during BP contained no REM sleep, 8 of those sleep episodes occurred during the day, and 7 occurred between 2PM and 10PM. Finally, Figure 4 graphically points out the tendency of REM sleep to occur differentially at intervals across the 24-hour day, with maxima and minima of the circadian oscillation occurring between
4 and 8AM and 4 and 8PM, respectively. Such data seem to underscore the tendency for REM sleep to occur differentially across the 24 hours.
The decrease in REM percent during the bedrest period, compared to baseline, also appears to have been the consequence of the circadian placement of REM sleep. While total REM time was differentially obtained within a relatively circumscribed time block, total sleep time was influenced somewhat less by such contingencies. In addition, opportunities for day sleep, when REM was less likely to occur, occupied a larger percentage of the bedrest period than did night sleep time. As a result, over the bedrest period, absolute sleep time was augmented to
a greater extent than was REM time, thereby lessening the proportion of TST spent in REM sleep.
The decreased proportion of REM sleep recorded over the bedrest
period may also be attributable, in part, to the decrease in mean sleep period length, relative to baseline, associated with BP. It has been shown that the amount of TST spent in REM sleep becomes proportionately less with the reduction of sleep length (Webb and Agnew, 1977). Since mean sleep period length during the bedrest period was almost two..thirds less than that for the baseline night (2.99 hrs. vs 8.75 hrs.), a corresponding decline in the proportion of REM sleep for the majority of sleep periods during BP would also be expected.
The observed decrease in REM percent, however, may also be a
reflection of the decreased mobility and/or lack of novel perceptual stimulation characteristic of the bedrest situation. Several investigations of sleep patterns during prolonged bedrest have reported similar declines in REM sleep (Aserinsky, 1969; Nakagawa, 1980; Ryback and Lewis, 1971). In addition, Adey, Bors and Porter (1968) reported decreased
porportions of REM sleep -in quadraplegic patients, relative to normal amounts. The authors proposed that the diminished REM sleep was related
to "loss of most motor performance in the waking state," as well as the "absence of highly focused attention in complex motor activity." The finding by Ryback and Lewis (1971), that subjects who were permitted no exercise while confined to bed exhibited decreased REM sleep, while those who were allowed to exercise during bedrest did not exhibit such a decline, also provides some support for this notion. In the present study, the finding that REMS percent decreased (albeit slightly) from the first to th second 24 hours, may likewise be interpreted as supporting an immobilization/sensory habituation effect on the amount of REM sleep obtained.
A rather unexpected fli ding in the present study was that of an increase (though not significant) in the proportion of SWS, as the bedrest period progressed. In their examination of patients with high crevical lesions, Adey et al. (1968), reported the diminution of SWS as well as decreased REM percentage. As with REM sleep, the authors concluded that such a decline was the consequence of immobility. Thus, the findings of the present study appear contrary to what would be expected by an immobilization hypothesis.
On the other hand, the results reported here are in accord with the findings relative to SWS reported by Ryback and Lewis (1971). The bedrest subjects in that study exhibited increases fn SWS with the nonexercise group showing the larger rise. These results were interpreted by the authors as indicating that SWS may serve to "repair or maintain the muscular system" in response to the effects of atrophy, as well as hypertrophy. Thus, it would appear that a change in the proportion of SWS, in either direction, may be explained by one or the other version of an immobilization hypothesis.
However, it seems somewhat unparsimonious to have to employ both versions to satisfactorily explain the data in terms, of immobilization. In the present study, SWS comprised a smaller proportion of TST during BP than during the baseline night. The hypothesis proposed by Adey et ai. is useful in explaining such results. Yet, within the bedrest period, there was an increase in the percentage of SWS from the first to the second 24 hours. These findings clearly require the Ryback and Lewis version.
Several observations seem to support an alternative explanation for the increase in SWS across the bedrest period, however. It has been shown (webb and Agnew. 1971, p. 1354) that "longer periods of
wakefulness before sleep result in greater amounts of stage 4 sleep in the first 3 hours of sleep." In the present study, the mean inteval between sleep episodes increased by some 70% (from 1.65 hrs. to
2.82 hrs.) from the first to the second 24-hour period. At the same time, the proportion of SWS increased almost 25% (from 12.9% to 16%). By the same token, periods of wakefulness between sleep episodes averaged about 1 hour longer during the day than at night (3.32 hrs. vs
2.29 hrs.). Correspondingly, SWS comprised a slightly greater proportion of day sleep than of night sleep episodes (16.2% vs 13.2%). The relationship between prior wakefulness and subsequent amounts of SWS seems apparent.
Such an association would also account for the decline of SWS
from Night 2 to the bedrest period. The amount of wakefulness preceeding the baseline night (14 to 17 hrs.) far exceeded the duration of waking intervals characteristic of BP. Consequently, the subsequent sleep periods reflected this difference by exhibiting differential
proportions of SWS sleep. Inconsistent with a prior wakefulness hypothesis, however, is the observation by several investigators that there is a SWS 'kick' in the records of extended sleep. That is, extended sleep is oftLen characterized by the reappearance of substantial SWS episodes in the late morning. The possible significance of such a finding is considered later in the discussion.
Results of the examination of the influence of prior sleep on the REM sleep cycle are best described as equivocal. Two examinations were made, one to test the notion that the REM cycle is sleep-dependentIC, the other to examine the possibility that the REM cycle is, instead, a sleep-independent rhythm based on elapsed cluck tLime, regardless of stat e. Support -for both views may be found in the literature. For example, Globus (1966) found that the cycling of REM sleep demonstrated "at least in part" a tendency -to be a time--locked, rather than a sleep-dependent, rhythm in the nap sleep of 2 subjects recorded for a total of 107 REM periods. This conclusion was based primarily on thle observation that correlations between sleep onset and REM onset decreased at certain times -in the afternoon (between noon and 3 PM). That is, during this interval sleep onset got progressively later while REM onset remained constant relative to real time. Yet, prior sleep was not considered and, therefore, the interpretation of such findings is problematic.
In contrast, Moses et al. (1975) and Moses, Lubin, Johnson, and Naitoh (1977) reported findings which suggest that the REM sleep cycle is a sleep-dependent phenomenon. In the 1977 study, the nap sleep of
25 subjects was 'compressed,' by subtracting all intervening waking periods, and then examined as a single sleep episode. The resulting
mean REM cycle lengths did not differ significantly from those recorded
during baseline sleep. The same procedure was carried out in the present study, and similar results were obtained. Using the-onset of the last REM period of Night 2 as a starting point, the mean REM cycle length was determined for subjects' 'compressed' bedrest periods, and compared to the mean cycle length for Night 2, The mean cycle length for the compressed period differed from the cycle length for Night 2 by less than 1 minute (96.84 min vs 96.56 min). Such evidence is strongly suggestive of a-sleep-dependent-cycle.
In a second test, each subject's mean REM cycle length for Night 2 was superimposed on both his/her 'intact' bedrest period (i.e., including waking periods) and compressede' bedrest period. The mean deviation of an actual REM occurrence, from the onset of the hypothesized cycle, was used as a measure of 'goodness of fit.' The mean deviation across the 'compressed' bedrest period was 14.5 minutes. In other words, the actual occurrence of REM periods during BP differed by an average of about 15 minutes, as compared to expected occurrences, when intervening waking episodes were disregarded. Again, such a finding is supportive of a sleep-dependent REM sleep cycle. However, a similar finding that
the mean deviation of actual REM sleep from hypothesized REM periods across the 'intact' bedrest period (15.8 min), precludes the acceptance of the sleep-dependence of REM sleep at the absolute exclusion of the 'real time' model.
Numerous studies of napping and dispersed sleep (Carskadon and Dement, 19.75: Globus, 1966; Moses et al., 1915; Nakagawa, 1980; Webb et al., 1966) have reported perturbations in the mode of appearance of REM sleep episodes, characterized by the onset of REM sleep within minutes of the initiation of a sleep period. The reported frequencies
of occurrence Of Suich sleep onset REM periods (SOREMPS) have ranged from as few as 311 out of '107 REM episodes (Globus,. 1965) to as many as 21 of 34 REM episodes (Moses et al,, 1975). Maron et al. (1964) reported tLhe Occurrence of no REM onset periods in the examination of 18 subjects who napped in either the afternoon (about 1 :30PM) or evening (about 7:30PM). Yet, the overall rate of occurrence of SOREMPS for 5 studies of dispersed and nap sleep (Carskadon and Dement, 1975; Globus, 1966; Moses et al., 1975; Nakagaua, 1980: Weitzman et al., 1974) is rather
substantial at 39% of all REM periods recorded (range 2.8% 72%). Since such events are almost never observed in normal nocturnal sleep, SOREMPS have been considered to be indications of the overall disruption of normal sleep structure associated with day sleep episodes and
dispersed sleep regimens (Weitzmian et al ., 1974; Mloses et al., 1975).
In the present study, of 153 REM episodes recorded over the bedre1st period, only 3 were initiated at the beginning of a sleep period (i.e., before the appearance of 2 min of stage 2). The infrequency of such occurrences suggests that the dispersed sleep of the present study may be of a different sort than typically observed nap sleep or experimentally dispersed sleep.
Suich a view is further supported by the regularity with which sleep stages occurred across the bedrest period. Seventy percent of all- sleep
periods recorded during BP were 'full blown' sleep episodes (61% of day sleep episodes); that is, all sleep stages were present. By comparison, only 16% of the 550 opportunities for sleep in the Weitzman et a]. study contained all stages. Of the 80 naps examined by Moses et al. (1975), 27.5% contained both SWS and REM sleep. REM sleep occurred in 90% of
all sleep episodes during BP (86% of day sleep episodes), SWS occurred
in 85% of the sleep periods in this study (80% of day sleep periods),
Again by comparison, the naps of subjects studied by Moses et al. contained REM episodes 43% of the time; 35% of the sleep opportunities examined by Weitzman et al. contained REM and 48% contained SWS.
Seven of the 9 sleep periods which contained no REM sleep occurred between 2PA and 10PM. Such a finding is consistent with previous ones that REM sleep typically increases in amount from midnight to morning and decreases toward evening (Moses et al., 1975; Nakagawa., 1980; Wei'tzrnan et al. 1974). It is likely, then, that the absense of REM during some sleep episodes in the present study were, at leas In part,, due to circadian effects.
A similar possibility also exists relative to 'missing' periods of SIAS (specifically, stage 4). Several examinations of extended
sleep (see for example, Gagnon and Dekoninck, 1981; Webb, Campbell and Hendlin, 1981) have noted the re-occurrence of stage 4 (in relatively large amounts) during the late morning. In the present study, sleep episodes characterized by the absence of stage 4 occurred across the entire day (6:40AM to 10:45 PM). It is interesting to note, however, that an obvious 'gap' occurred between 10:30AM and 2:20PM. That is, the sleep episodes initiated during those four hours always contained
stage 4 sleep. Sleep periods initiated after about 11PM,. and throughout the night, also contained stage 4. Thus, it might be suggested that the absence of stage 4 in 15% of the sleep episodes in this study, was the manifestation of the biphasic cycling of stage 4 sleep, rather than a reflection of the disruption of normal sleep processes. A further indication of the possible bipolar nature of stage 4 is the observation that total stage 4 time for BP was evenly distributed between day and night (716' min vs 714 min).
Clearly, the differences in the appearance and sequencing of sleep stages between this study and the 2 studies of nap sleep with which it has just been compared, are attributable in large part to the difference in mean sleep episode length (3 hrs. vs 1 hr.) This i~s espccially true of REM sleep, if sleep dependency is assumed. Nevertheless, the persistence arid regularity with which sleep stages occurred across the bedrest period is noteworthy. There were no significant differences in the proportions of sleep stages between bedrest sleep and Night 2 sleep. Nor, were there significant changes in sleep stage percentages between the first and second 24 hours of bedrest. Finally, only REM sleep percent varied significantly relative to day or night onset times.
Weitzman et al. (1974) noted that the sleep episodes which they observed were "clearly not minatures of the normal 8 hr. sleep pattern." Such a view has been echoed by most others who have studied dispersed sleep and naps. Most of these studies have differed from the present one, in that the sleep periods were typically experimentally circumscribed, rather than being placed on a 'self-demand' schedule. Such a methodological difference may account for the dissimilarity of results reported here.
Yet, Nakagawa (1980) also reported significant differences in day episodes versus baseline (night) sleep, despite the-fact
that the onset and termination of sleep periods was not regulated. Significant increases in stage 1, significant decreases in stages 4
and REM and the presence of SOREMPS led Nakagawa to conclude that "daytime sleep itself might be characterized as a special sleep at the onset of the diurnal sleep-waking cycle," (p). 534).
In that study, Nakagawa noted a sleep/waking cycle of approxi.mately 4 hours, and suggested that a significant relationship seemed to exist between this cycle and the scheduling of meals. The quadriphasic rhythm observed during the present study did not appear to be the result of feeding schedules, since less than half (42%) of waking periods were used for meals. Further, one subject (#932) fasted
for the duration of the experiment, yet maintained the least variable sleep/waking cycle of the group.
Uniphasic or Ultradian? The results of the present study seem to suggest, then, that the daytime sleep observed was not a "special" sleep, but rather was the continuation of an ultradian sleep/waking rhythm, which nevertheless maintained a definite tendency to be weighted toward a nocturnal placement, relative to total sleep time.
The regularity with which sleep episodes were initiated across the bedrest period also seems to support the notion- of an ultradian pattern of sleep. The mean within-subject variability of the sleep/ waking cycles was 2.66 h (=SD). While the between-subject variability was similar (SD =2.73), most of the variability was contributed by a single subject. This subject (#946, see Table II) exhibited a sleep/waking cycle (13.59 h) which more than doubled the mean sleep/ waking cycle length of the other 8 subjects (5.85 h). Likewise, the
variability of the sleep/waking cycle of this subject (OD = 4.52) exceeded the group mean by almost twice (SD m2.43). Excluding this
subject's sleep/waking cycle length from the group mean reduces the
variability of the quadriphasic rhythm to less than an hour (SD 57 min).
Such a pattern of variability is similar to that A so rved for the REM sleep cycle. The 90 to 100 minute REM cycle is of limited value in predicting the occurrence of REM episodes within the sleep record of a single subject. Yet for a population, the predictability of a 90-100 minute cycle is quite good.
A further indication of the regularity of the quadriphasic sleep/ waking cycle is the observation that the overall cycle length did not change significantly from one 24 hour period to the next. On the other hand, the length of the sleep/waking cycle did differ as a function of day and night, with the night cycle being substantially longer (7.8 hrs. vs 5.2 hrs.). 'It might be speculated that this difference was the consequence of subjects having spent the majority of their lives entrained to a monophasic sleep system, and that given time, the difference in cycle lengths might diminish. The present data do not support such a notion, however since the difference between night sleep/waking cycle length and day sleep/waking cycle length did not lessen significantly in the second 24 hours of bedrest.
The polyphasic distribution of the sleep of numerous animals under experimental conditions is well documented. Berger (1972) has noted that "if we wish to study comparative aspects of normal sleep, we shouldn't impose wakefulness at any time on any species, including the human, but should take 24-hour recordings under equivalent conditions." The relatively basal activity levels, absence of novel perceptual stimulation and the satisfaction of bodily functions
characteristic of the present experimental situation are comparable
to typical conditions under which animal sleep is studied.- That a polyphasic sleep pattern was exhibited under 'such conditions, therefore, was not completely unexpected. Indeed, in 1972 Snyder speculated that "even in the human we would probably find polyphasic sleep if we used the same conditions that we use for animals," (p. 45),
While the monotony of the situation was quite likely instrumental in the increase in total sleep time over the bedrest period, it seems less probable that such "neurological boredom" would be expressed in a cyclic manner. Yet, the possibility remains, as noted by Weitzman (1972) with regard to the sleep cycle in cats. "In your experimental situation, you are measuring in part the shift o~f pattern which is taking place from a previous long-established light-dark pattern, inl addition to adaptation to a strange new environment. Are you measuring the effect of that shift as well as the intrinsic rhythmicity in the cat? If the measured rhythmicity were constant over, say, several weeks, thenit would support the concept that a basic rhythmicity was beinj measured, However, if it tended to change over 1, 2, or 3 weeks that would suggest that you are at least partially measuring an adaptation effect," (p. 201). Obviously, the question relative to human sleep cannot be resolved by results of the' present experiment.
It is suggested, though, that the conditions of the present study
represented a further advancement along a continuum of slackened behavioral controls over the sleep process, the results of which was a
clearer manifestation of an inherent ultradian sleep/waking rhythm, rather than the adaptation of the sleep response to a "strange new environment." It is further suggested that such a rhythm, albeit in
highly dampened form, may also be reflected in the occasional naps taken by normal adults (especially on weekends), the increased frequency of naps associated with the loosened schedules of geriatric and college populations, the sleep patterns of infants, and the polyphasic sleep patterning noted in unstructured environments (i.e., Arctic expeditions).
And, I would suggest one additional manifestation of the ultradian nature of the sleep response. Webb (1969) has noted that "(no one yet has exploited a foundation to study the 'siesta' patterns of the tropi-cal and subtropical cultures, although at various odd moments, I am most tempted),' (p. 58). Results of the present study may suggest that such a proposal, to examine cross-cultural diversity in the cycling of rest and activity, .may deserve a better fate than parenthetical consideration.
I. How many hours, on the average, do You usually sleep per night?
less, 5, 51, 6, 61, 7, 7i5 8, 81, 9, 95, 10, more
2 How many hours of sleep per night do you think that you need to
feel well Ad function adequately?
3, How many hours of sleep per night do you prefer to have when You
have a chance?
4. In general, the amount of sleep that you usually get is:
not enough about enough too much
5. On the average, about how many naps do you usually take each week?
0, 1, 2, 3, 4, 5, 6, 7, 8, or more
6. About how many total hours do you usually spend each week taking
7. About how many times on the average do you wake up each night?
0, 1, 2, 3, 4, 5, 6, 7, 8, or more
8. About how much total time do you spend awake after going to sleep?.
none, less than 5 min., 5-15, 16-30, 31-60, more
9. About how many minutes does it typically take for you to go to
sleep? less than 5, 5-15, 16-30, 31-60, more than 1 hour
10. How often do you have trouble getting to sleep as quickly as you
would like? Almost never, occasionally, often, almost always
11. How much do you enjoy sleep?
not at all, a little, moderately, much
12. How regular are your bedtimes?
very regular, somewhat regular, somewhat irregular, very
13. How regular are your wake-up times?
very regular, somewhat regular, somewhat irregular, very
14. What is your average bedtime during weekdays? TO nearestl min-T
15. What is your average bedtime on weekends?
o nearest 15 m5j
16. What is your average wake up time on weekdays? (to nearest ITAT'n.7
17, What is your average wake up time on weekends?
To nearest 15 min.
IT How well do you usually sleep at night?
Very well, satisfactorily, some problems, poorly.
19. Do you usually feel well rested when you wake up, or soon thereafter?
Almost never, occasionally, often, almost always
20. On the average, how many days per week do you usually go to bed
acre than one (1) hour earlier or later than your average bedtime?
0, 1, 2, 3, 4, 5, 6, 7
21. On the average, how many d ays per week do you usually wake up Tfiore
than one (1) hour earlier or later than your usual wake up time?
0, 1, 2, 3, 4, 5, 6, 7 .
22. Do you consider your sleep very light or very deep? Check below.
very light-- -. very deep
23. Do you feel tired during the day because you have slept poorly?
Never sometimes often always
24. How much alcohol do you drink?
Never sometimes everyday
25. Do you wake up before you intend to?
once or twice a month
---once or twice a week
nearly every day
26. Do you use sleeping pills to get to sleep?
about once a month
_--about once a week
27. What, if any, sleeping pills do you use?
28. What, if any, prescription drugs are you presently taking?
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Scott Searcy Campbell was born February 25, 1952. HeI received his B.A. degree, with a major in psychology, from Florida State Univers ity in 0974. From September, 1972, to June, 1978, he attended Montana State University from which he received the M.S. degree in experimental psychology. In September, 1978, he continued his graduate studies, under the supervision of Wilse B. Webb, at the University of Florida. Upon completion of the Ph.D. degree, he accepted a postdoctoral fellowship at Harvard Medical School.
I certify that i have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.
lot,__Wise B. Webb, Chairman Graduate Research Professor of Psychology
1 certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.-------William K. Berg
Professor of Psychology
I certif y that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.
Donald A. Dews bury
Professor of Psychology
I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the deg~ree-'of Doctor of Philosophy.
Charles M. Levy
Professor of Psychology
I certify that I have read this study and that in my,; opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.
W/Uack R. Smith
Professor of Electrical
This dissertation w~as submitted to the Graduate Faculty of the Department of Psychology in the College of Liberal Arts and Sciences and to the Graduate Council, and was accepted as partial fulfillment of: the requirements for the degree of Doctor of Philosophy.
Augus 1979Dean for Graduate Studies and Research