THE ESTIMATION OF SLEEP QUALITY IN DIFFERENT STAGES AND CYCLES OF SLEEP
Vadim S. Rotenberg email@example.com
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February 28, 2013
J Sleep Res (1993) 2, 17-20
Dream content in NREM and REM sleep correlates with the subjective experience of having slept immediately before awakening The estimation of depth of sleep depends on the quality of the NREM sleep stages The presence of dreaming in a given sleep stage is more important for the subjective experience of having slept than the duration of the sleep episode before the awakening Neurotic insomniac patients more often deny mental activity when awoken from NREM and REM sleep, than do healthy subjects These data suggest that spontaneous awakenings in different sleep stages, especially in the first sleep cycle, correlate with the insomniac's tendency to underestimate sleep duration and quality.
KEYWORDS: dreams, NREM, REM, sleep depth.
The peculiarity of the subjective estimation of sleep quality in different sleep stages may help us to understand the functional meaning of these stages One of the first systematic investigations of the subjective estimation of sleep duration after artificial awakenings out of different sleep stages and sleep cycles (Danilin and Latash 1972) revealed a fairly accurate estimation of the previous sleep duration after awakenings from REM sleep, whilst sleep duration was underestimated after awakenings from slow wave sleep (SWS) Although a careful analysis of such relationships could elucidate the importance of mental activity in sleep as a source for complaints in insomniac patients (Rotenberg 1980, Knab and Engel 1988), this topic has received little attention For instance, there are no reports on systematic investigations of the subjective quality of sleep in relation to different sleep stages and their durations The aim of the present investigation was to assess the subjective experience of having slept and the estimation of sleep quality, for different sleep stages and sleep cycles, in healthy subjects and in neurotic patients with insomnia The following two hypotheses were investigated (1) the underestimation of the quality of sleep after awakenings is more typical for neurotic subjects than for normal subjects, (2) the estimation of sleep length (in healthy and neurotic subjects) depends on the prior sleep stage, the duration of this sleep episode, and the presence or absence of mental content.
75 patients (43 women and 32 men), mean age 31 years (age range 20-39 years), with different neurotic syndromes (depression-28 Ss, anxiety-17 Ss, hypochondriasis-21 Ss, conversion hysteria-9 Ss), all with a complaint of insomnia, were compared with a group of 15 healthy volunteers (9 women and 6 men), mean age 29 years (age range 20-35 years), without any sleep complaint Patients were selected from an outpatient clinic, based on the clinical diagnosis of neurotic disorder They had to be free from medication for at least 3 weeks before the investigation.
Design and procedure.
All Ss were investigated polysomnographically for three consecutive nights The first night was for adaptation In the second night sleep was recorded without enforced awakenings During the third night Ss were repeatedly awoken in different sleep stages and sleep cycles, and gave their reports As a rule, one awakening was performed in SWS, usually in the 1st or 2nd sleep cycle Five patients with SWS in the 4th cycle were additionally awoken in this cycle In a few patients without any SWS, it was decided to perform two awakenings in stage 2 sleep when this stage contained some delta activity Such additional awakenings in stage 2 sleep were also performed in six of the healthy Ss.
For all Ss, at least two awakenings were performed during REM sleep, in different sleep cycles In addition, reports were also collected after spontaneous awakenings out of REM sleep The total number of awakenings never exceeded six per night.
We tried to perform the awakenings after at least 10 minutes of SWS or five minutes of REM sleep However, some patients awoke earlier and spontaneously, and gave reports To control for this factor, a similar number of early awakenings were performed in healthy Ss.
After each awakening Ss were asked the following questions:
(1) Were you asleep just before the awakening.
While sleep mentation in different sleep stages was investigated in all 15 healthy Ss, the subjective estimation of sleep depth was only able to be obtained from ten Ss. For the analysis of sleep mentation only unambiguous reports were used . For example, if the subject denied being asleep, but at the same time was not sure whether he/she had thoughts or dream-like experiences, we excluded the report from analysis On this basis 11 reports (3%) were excluded.
Definitions of mental activity in sleep.
'Definite thoughts' = reports with thought-like activity 'Indefinite thoughts' = reports such as "There were some thoughts but I cannot remember them exactly" 'Contentful reports' = the subject realised that he/she had a dream and could give a report of the content 'Contentfree reports' = the subject realized that he/she had a dream but could not give a definite report about its content 'No dreams at all' = the subject denied dream experience.
Polysomnography and sleep staging were performed according to the guidelines of Rechtschaffen and Kales (1968) For statistical analysis, the Chi-squared test was used.
A total of 34 awakenings were performed in stage 2 sleep in the patients, and six in healthy Ss 163 awakenings were made in REM sleep in the patients and 53 in the healthy Ss In SWS there were 54 and 21 awakenings, respectively (see Table 3) Table 3 contains more reports from healthy Ss than do Tables 1 and 2 (see below) We have concentrated on REM sleep and SWS awakenings, because in our previous investigations (Rotenberg 1980) as well as in studies performed by Danilin and Latash (1972), the most impressive differences were found for these two types of sleep The distribution of the subjective reports according to sleep stages and sleep cycles is shown in Table 1 It can be seen that denial of sleep occurred in 20 reports after awakenings from REM sleep, almost exclusively (n = 19) in patients, and in 39 reports after awakenings from NREM sleep, again, almost exclusively (n = 38) in patients At the same time, reports of 'deep sleep' were given after 106 awakenings from REM sleep (total number of awakenings in REM sleep =190), but only after 33 awakenings from NREM sleep (total number of awakenings = 116, difference between these REM and NREM values P<0001) Comparing the reports made after awakenings from different stages of NREM sleep, only after 5 awakenings from stage 2 (total number = 39) was sleep estimated to be deep, while it was estimated as deep after 28 awakenings from SWS (total number = 76, significantly different from stage 2, P < 0. 001) The denial of sleep occurred equally often after stage 2 and SWS.
Table 1. Numbers of cases reporting different sleep
qualities m different cycles and stages of night sleep.
Table 2. Number of cases reporting sleep quality according
to the length of stage
Sleep denial after REM sleep did not depend on the sleep cycle, and occurred in all sleep cycles. In contrast, the percentage of reports with sleep denial after awakenings from SWS was twice as high in the first cycle (18/53 = 34%) compared with the second cycle (3/18 = 17%). Awakenings from stage 2 in the first cycle contained sleep denial in more than 50% (7/12) of the occasions, while in second cycle sleep this fell to less than 20% (2/11).
Subjective reports claiming deep sleep after awakenings from SWS in the first cycle were more unlikely than in the second cycle Moreover, in 50% of these cases, reports of deep sleep were also accompanied by dream reports.
Table 2 shows the influence of sleep stage duration on the subjective estimation of sleep quality Sleep denial as well as reports of deep sleep were equally frequent when the stage duration before the awakening was between 6 and 10 or 11 and 20 minutes Following REM sleep episodes having a duration of less than five minutes, and compared with those having a duration of more than five minutes, sleep denial was more frequent (21% vs 8%), and the claim of sleep being deep was more unlikely (35% vs 58% P <0.05) All calculations are based on the total number of reports of sleep denial and deep sleep. Sleep denial became less common from an SWS awakening when the duration of SWS exceeded 20 minutes.
Thus, estimation of sleep depth was more dependent on the sleep cycle than on the duration of the preceding sleep stage Does this difference depend on the increase of sleep duration from cycle to cycle, or on the absence or presence of REM sleep in the segment of sleep before the awakening9 We found that the estimation of sleep quality did not depend on whether the sleep duration before the awakening was more or less than 90 minutes. However, if this sleep included REM sleep, then the awareness of sleep prevailed Sleep periods less than 90 minutes had a different influence on sleep estimation, depending on the absence or presence of REM sleep If REM sleep occurred in the sleep episode, then reports of deep sleep appeared more often, and sleep denial was rare (P < 0.05) If the sleep period exceeded 90 minutes, and excluded REM sleep, then reports of sleep denial prevailed, but if such sleep periods included REM sleep, then reports of deep sleep prevailed.
If the duration of prior sleep was less than 90 minutes, and this sleep did not include REM sleep, then reports of deep sleep occurred in only 18% of all reports, in half of all these cases Ss also reported dream experiences.
The difference in reports between healthy Ss and insomniacs was also very prominent The patients denied being asleep in 22% (57/261) of all awakenings, while this occurred in only 4% (2/45) of healthy subjects (P < 0.001)
Table 3 presents data on the mental activity in different sleep stages, including data on those five healthy Ss who were excluded from Tables 1 and 2 because they were questioned only in relation to sleep mentation, but not sleep depth Healthy Ss mostly presented contentful dream reports following REM sleep, and tended to make similar reports from SWS. Such reports from both REM and SWS were less likely in the patients, (P < 0 01), independently of clinical syndrome, sex, age and previous drug use
Table 3. Mental activity in different sleep stages (number and percentage of cases)
The present results suggest strongly that REM sleep and dreams are especially important for the awareness of the subject's own sleep, whereas the estimation of sleep quality (sleep 'depth') depends on the NREM stage before awakening In comparison to stage 2 sleep, SWS determines the perception of a more profound sleep The observation that the subjective estimation of sleep quality is more determined by the rank number of the sleep cycle than by the duration of the sleep stage before the awakening also confirms the importance of REM sleep, because every sleep cycle is completed by REM sleep The presence of REM sleep (or dream experience in NREM) seems to be more essential to the estimation of sleep quality than the duration of sleep before awakening.
However, in neurotic patients REM sleep often does not play the same role, as these patients denied having slept more often than did healthy subjects, even if the critical time span contained REM sleep The prevalence of dream denial and content-free reports in REM sleep in neurotic subjects suggests some insufficiency of REM sleep in these patients The latter may be responsible for the underestimation of the quality of prior sleep On the other hand, there are many spontaneous awakenings in NREM sleep in neurotic patients (Rotenberg 1980) which could also relate to the underestimation of sleep Thus there are at least two reasons for the underestimation of sleep quality and sleep length in neurotic patients (a) the increased number of spontaneous awakenings in different sleep stages, including awakenings in the first cycle and in all other cycles which do not contain REM sleep, (b) the reduction of dream-like mental activity m REM and NREM sleep.
Due to the role that dream activity may play in the process of psychological and behavioural adaptation (Greenberg and Pearlman 1974, Rotenberg 1984) one may suggest that a functional insufficiency of REM sleep in parallel with sleep underestimation is associated with the psychological maladaptation of neurotic insomniacs (Rotenberg 1988).
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Accepted in revised form 22 October 1992, received 21 July 1991