A Comparison of Mental Activity During Sleep Onset and Morning Awakening

Transcription

1 DREAM RESEARCH A Comparison of Mental Activity During Sleep Onset and Morning Awakening PierCarla Cicogna, Vincenzo Natale, Miranda Occhionero, and Marino Bosinelli Department of Psychology, University of Bologna, Italy Summary: The aims of the experiment were: (1) to establish the proportion of sleep stages in morning spontaneous awakening and to observe whether any stage-dependent differences can be found in the mentation reports; and (2) to compare the characteristics of mental activity during sleep onset (SO) and during the latest sleep period. One hundred forty-four dream reports and their association reports were collected from 36 subjects in a lab experimental design. Dream reports were analyzed as to structure (length, narrative continuity), content (self, setting, lab references, nonself characters, dimensional distortions, body feelings, bizarreness and emotions), and awareness (reality testing). Associations were classified as episodic, abstract self-referred, and semantic memories. The morning awakenings results were not affected by the stage of sleep during which dreaming occurs. SO reports prevalently show a lifelike nature, while sleep-offset reports are prevalently dreamlike. On the other hand, there seems to be a similar availability of mnemonic systems in the two sleep conditions. Key words: Dreaming; sleep onset; morning awakening; sleep/wakefulness transition; dream sources UNDER NORMAL CONDITIONS, spontaneous morning awakening has a clearly defined biological pattern. Before the awakening, body temperature, blood pressure, and heart-rate frequency all rise sharply. 1 These changes persist after awakening accompanied by others, such as a further increase in plasma levels of ACTH, aldosterone and cortisol, 2,3 and in colonic motility. 4,5 The fact that these changes occur before awakening (the preparatory phase), and are then accentuated by the awakening itself (the operative phase), suggests that there is a reciprocal regulatory link between the body and the awakening phase. The changes that precede spontaneous morning awakening seem to be designed to prepare the body biologically for a new period of wakefulness. A progressive predis- Accepted for publication March, 1998 Address correspondence and reprint requests to prof. Cicogna PierCarla, Department of Psychology, University of Bologna, Viale Berti Pichat 5, Bologna, ITALY position of the body toward awakening as the period of sleep progresses would seem to be indirectly confirmed by the fact that auditory awakening thresholds gradually decrease during the night and as the moment of spontaneous awakening in the morning approaches. 6 Circadian rhythmicity would appear to play an important part in the body s preparation for awakening. This impression is strengthened by the conclusions reached by Monk and Moline, 7 who, when studying free-running subjects, have observed that both phases of falling asleep and awakening tend to be synchronized with the circadian rhythms (for example, with body temperature, an important marker of the circadian rhythmicity). When this synchronization does not occur, periods of sleep are more variable and are frequently interrupted, with obvious effects on the circadian rhythmicity of alertness during the day. It is not yet clear what part is played by ultradian rhythms. While there is a precise biological circadian pattern which accompanies awakening, we have no such detailed information regarding the ultradian components. 462

2 Table 1. Mean percentages of REM and NREM awakenings in normal conditions and in free-running conditions. Normal conditions REM Stage 1 Stage 2 SWS NREM N Awakenings Webb, % 37.50% 37.50% 06.25% 81.25% Schulz et al, % % 8 47 Webb et al, % 18.43% 49.99% 02.64% 71.06% Weitzman et al, % % 9 40 Mean values 29.17% 70.83% Free running REM Stage 1 Stage 2 SWS NREM N Awakenings Webb, % 27.27% 31.83% % 2 22 Schulz et al, % % Weitzmab et al, % % Campbell, % % 9 84 Moline et al, % % 1 11 Mean values 50.98% 49.02% This is particularly true for the strictly electroencephalographic aspects: we are still not able to predict at what point sleep offset occurs. 8 The last transition in the morning from sleep to awakening can occur both in REM phase (30% of cases) and in NREM phase (70% of cases) Some authors, given evidence in free-running conditions that the percentage of awakenings during REM phase increases, 9,10,12-14 have hypothesized that the REM phase may act as a timing event which facilitates awakening. 12,15 If we consider the limited amount of data available regarding the stage of spontaneous morning awakening (see Table 1), it would seem reasonable to conclude that in normal conditions the REM phase is not a determining factor in controlling the awakening phase: even in conditions of complete isolation, the percentage of awakenings that occur during REM phase, though it increases, never exceeds 60%. There are numerous factors, then, which in normal conditions affect the phase of awakening: (1) the circadian rhythms 16 ; (2) the duration of the sleep period which precedes awakening, ie, the homeostatic rhythm 17 ; (3) the NREM-REM cycle, ie, the ultradian rhythms 18 ; (4) the photoperiod 19 ; and (5) the cognitive and motivational activity in particular, dreaming and expectations concerning the period of waking which is to follow. 14 On the basis of the considerations outlined above, we might conclude that the circadian rhythms are the most influential of these factors. Nevertheless, despite the considerable amount of information that has been gathered so far, it should be noted that many factors, such as physiological structure or mental activity during awakening, have not been sufficiently investigated, making Webb s remark that one of the most obvious and important phenomena of sleep has been one of the least explored the self-termination of sleep still appropriate (9, p. 984). Concerning the cognitive factors, only indirect observations are available, such as investigations into the ability to wake up at fixed times ; the results obtained in this field do not coincide, and only allow us to conclude that if such an ability does exist it is only to an insignificant degree. There would, however, appear to be some cognitive influence on the way the body prepares for awakening. But what about routine situations? One potentially fruitful line of research might be to investigate the mental activity of the subject during spontaneous morning awakening. Very little research has been done on dreaming during morning awakening. The fact that there is no elective awakening stage, along with the fact that research into dream production has long been rigidly stage-dependent, may have discouraged research in this direction. To date there have been only two pilot works on this subject, 25,26 both of which produced comparable results in terms of content and of the mnemonic sources involved in dream generation. Dreams produced immediately before morning awakening are shown to be rich, with complex plots, and frequently containing bizarre elements. Both studies report a prevalence of episodic mnemonic sources related to events recently experienced by the dreamer. This link to the wake subjective experience supports the idea that the last morning dreaming also has a preparatory role for the next wakefulness. Experimental research in recent years has shown that, contrary to initial hypotheses that are centered on the rigid REM/NREM dichotomy, dreaming can occur in every stage of sleep, and the percentage of recall even in NREM sleep is frequently higher than 50%; for example, we found a dream-recall value of 64.53% in slow-wave sleep. 28 We assume here that the dream can be defined as a mental experience during sleep, characterized by a narrative structure, with perceptual components, frequent feeling of self-participation, possible bizarre elements, and, usually, loss of reality testing. Psychophysiologic research 463

3 on dreaming in the last 15 years has suggested the hypothesis that the cognitive processes underlying dreaming can be the same, but can operate in various stages at different levels of engagement. We believe that the notion of a single dream generator is to be preferred to the hypothesis of a two-generator, both because the two-generator hypothesis is a little parsimonious, and because the differences between REM and NREM mentation are not so significant as to justify the hypothesis of two different production systems. The quantitative differences (ie, the number of memories available for dream generation and the length of reports) are important and reliable factors for discriminating dreams in different stages of sleep. 28,30-32 Nevertheless, recent studies have shown that the mental activity occurring during the first sleep onset (SO) differs, in terms of its quantitative and qualitative characteristics, from that occurring in other sleep conditions. 29,33,34 In fact, SO dream reports are more lifelike, ie, less implausible and bizarre, than those of other REM and NREM sleep conditions, and daytime residues are more numerous than in REM reports. The mnemonic sources of SO dreams mostly stem from the episodic memory system; that is, they refer to specific and personal events. 26,29 SO dreaming could ensure a continuity of self-experience across a sort of carryover effect from the previous waking. If the transition from waking to sleep explains some of the peculiarities of the initial sleep period, it seems reasonable to presume that the transition from sleep to wakefulness must also affect the mental activity of the last sleep period. Dreaming which occurs just before spontaneous awakening could also prepare subjects for the next state of wakefulness. Since awakening is preceded by a long period of sleep, it is possible that the dreaming generated at this moment is influenced by previous oneiric activity: as with sleep onset, there may be a sort of carry-over effect from the preceding condition of consciousness. The hypothesis of a cognitive preparation for awakening is also consistent with the physiological data related to awakening mentioned earlier. On the basis of the considerations outlined above, the aim of this study can be summarized as follows: (1) to establish the proportion of sleep stages in morning spontaneous awakenings and to observe whether any stagedependent differences can be found in the related mentation reports; and (2) to compare mental experiences and memory sources in two phases of transition, wakefulness vs sleep and sleep vs wakefulness. We hypothesize that there must be distinguishing characteristics between these two conditions of consciousness, and that these characteristics can produce significant differences in the mentation during SO and sleep offset. The first point mostly concerns the sleep-offset condition, as well as the reports collected after spontaneous awakenings in that condition. The SO dream reports, on the other hand, were collected after artificially provoked awakenings. We do not believe that this difference (spontaneous vs provoked awakenings) invalidates any comparison of the related reports and the evaluation of the results. Given that our aim was to study the characteristics of the last dreams before awakening in preparation for wakefulness, it is important that the recorded dreams really be the last experience before spontaneous awakening. Awaiting spontaneous morning awakening gave us two advantages: first, it allowed us to check the stage in which our subjects naturally woke up; second, it allowed us to test stage-dependency by comparing mental experiences collected from different stages. In conclusion, we could usefully compare dreams recalled after a provoked awakening at SO-stage 2 with the dreams collected after a spontaneous morning awakening at the end of sleep. It would seem reasonable to hypothesize that the characteristics of the mentation immediately before morning awakening are not significantly affected by the stage in which awakening takes place. As far as the second point is concerned, we expected the dreams generated before morning awakening to be more dreamlike (similar to those generated during the night) than those generated during SO. We expected that the sleep-offset reports to show a higher degree of self-representation (ie, the dreamer s presence in the scene), more perceptive properties, and more bizarre elements than the SO reports. On the other hand, for two different reasons we did not expect to find any significant differences in the quantity of emotions between SO and morning awakening. First, previous studies have shown that dreams during SO contain fewer emotions than REM and NREM dreams during the night, a phenomenon which would appear to be caused by the need to reduce those elements which might render falling asleep difficult, such as high levels of emotion. Second, it has been suggested that one of the functions of dreams is to metabolize tensions and emotions accumulated during the day ; given this hypothesis, we expected the last mental experience before awakening to contain fewer and less intense emotions than those experienced in the middle of the night. Concerning the subject s degree of awareness, we expected to find a higher incidence of experiences with loss of reality testing (ie, the dream seems to the subject a real experience) in the morning awakening than in SO. Regarding memory contents activated as the sources of the dream experience, 40 we hypothesized that in both conditions, specific episodes or events which the dreamer had experienced would be more frequent than content which was related to general or semantic knowledge. 25,26 It should be noted that previous studies 28,29 had shown that the memory contents activated as dream sources during the night, both in REM and in NREM, contained equal 464

4 amounts of specific episodes from the dreamer s life, general self-references, and semantic contents. The hypothesized prevalence of memories of real events in the dreams before morning awakening would appear to prepare the subject for the return to wakefulness, while a similar prevalence in SO dreams would be the result of a lingering consciousness of the events belonging to the condition of wakefulness that the subject is in the process of leaving behind. METHOD A sample of 144 dreams was analyzed, provided by 36 paid university students (16 males and 20 females), who were good sleepers and dream recallers, aged between 19 and 26. After an adaptation night to sleep laboratory, they were studied for 2 nonconsecutive nights each, under standard electropolygraphic control (two EEG channels, two EOG, and one EMG). Two mental experiences were solicited, via intercom, per night, one after awakening in SO, stage 2 (3 minutes after the first sleep spindles), and another immediately after spontaneous awakening in the morning. Immediately after the dream report, the subjects were asked to evaluate reality testing and intensity of emotions (scored on a sevenpoint scale). Whenever an awakening in a certain condition failed to produce a content report, additional nights were scheduled until a report was produced, to obtain four reports per subject. The dream report was segmented on line by the interviewer into thematic units. A new thematic unit was noted whenever a change in character, in the prevailing activity, or in the setting occurred in the dream report: eg, I was in my bedroom (first thematic unit)/ suddenly a big man came into the room (second thematic unit). Immediately after each of these short segments, the subject, previously trained, was invited to identify the immediate memory sources of the segment he/she had just related. 40 Sleep Parameter Scoring The sleep parameters of the entire night, submitted to a judge, were visually scored on computer screen using standard criteria. 41 The following sleep parameters were investigated: (1) total recording time, total sleep time, SO latency (first and second SO), REM sleep latency (expressed in minutes); (2) number of REM periods; (3) percentages of total REM sleep (total sleep record/total sleep time) and sleep efficiency; and (4) time of SO and time of awakening (expressed in time of day). Dream Reports Scoring Dream reports were submitted to two independent judges. The reported mental experiences were analyzed in terms of: (1) structure length of reports, only for morning awakening, scored in temporal units (any activities or single scene) and percentage of multiunit reports 31 ; narrative continuity (reports which contained more than one temporal unit were scored continuous whenever they showed a consistent narrative plot); (2) awareness reality testing (lost, uncertain or maintained); (3) content the presence of a setting, laboratory references, the number of non-self characters physically present, chromatic-dimensional distortions (images bizarre in shape, color or dimension), spatiotemporal distortions (implausible reports according to spatiotemporal waking standards); implausibility (global bizarreness), body feelings, the number of emotions clearly expressed by the dreamer, the intensity of emotions (scored by a seven-point scale), the presence of the dreamer and the characteristics of dreamer s participation. The self-participation characteristics were scored by an eightpoint scale 42 : (a) no participation; (b) awareness of one s own thoughts; (c) static representation of oneself; (d) representation of oneself as passive observer of the events of the dream; (e) precise awareness of oneself, both mental and physical, analogous to wakefulness; (f) awareness of oneself maintained through identification with other characters of the dream; (g) double representation of oneself (eg, the dreamer is simultaneously actor and observer); and (h) awareness of that this is a dream experience (lucid dream). Agreement percentage was >88% for all dimensions considered. Judges then resolved their scoring discrepancies, and the reconciled version was used in data analysis. Memory Sources Scoring Transcriptions of memory source reports were then submitted to the two judges who had previously scored dream reports. Memory sources were classified into the three following memory categories: Strict episodes discrete episodes in the life of the dreamer with precise spatiotemporal coordinates (eg, It reminds me of last Sunday when I went to a party at George s house ). Abstract self-referred memories referring to the dreamer s general knowledge of himself and his own habits (eg, It reminds me of my fondness for rock music ). Semantic knowledge elements of general knowledge of the world, including episodes from the biographies of others (eg, It reminds me that the Eiffel Tour was built on the occasion of the Universal Exposition in 1889 ). The strict episodes were classified into: Day residues memories referring to the day prior to the 465

5 Table 2. Means and standard deviation of time of sleep onset (TSO), latency of the first sleep onset (SOL1) and the second sleep onset (SOL2), REM latency (REM-L), number of NREM/REM cycles, time of spontaneous awakening (TA), total record time (TRT), total sleep time (TST), percentage of REM sleep (total REM sleep/total sleep time), sleep efficiency (SE) (TST/TRT). The bottom panel shows the awakening stages. Adaptation Night1 Night 2 night TSO 00:27 ± 00:35 00:15 ± 00:26 00:18 ± 00:31 SOL ± ± ± SOL ± ± REM-L ± ± ± NREM/REM 4.00 ± ± ± 0.94 Cycles TA 07:25 ± 00:54 07:36 ± 00:47 07:24 ± 00:41 TRT ± ± ± TST ± ± ± REM 17.42% ± % ± % ± 4.90 SE 86.53% ± % ± % ± Awakening stage St % 16.66% 11.11% St % 52.78% 52.78% SWS 6.25% 2.78% 11.11% REM 35.50% 27.78% 25.00% experiment. Recent events memories referring to the past year. Past events memories going back more than a year. Prospective events memories referring to future events. Interrater reliability (two times number of associations scored in common divided by the total number of associations scored by both judges) was >.81 for the classification of memory sources. As in the case of dream report analysis, judges resolved their scoring discrepancies, and the reconciled version was used in data analysis. RESULTS Sleep parameters were not significantly affected either by the experimental conditions, adaptation night vs experimental nights, or by the order of the experimental nights, first vs second night (see Table 2). Morning awakening occurred more frequently in NREM (73.61%) than in REM (26.39%), in line with previous data (see Table 1). Average dream recall rates were 73.33% for sleep onset and 92.62% for morning awakening (95.00% in REM awakening and 90.74% in stage 2 awakening). Concerning morning-awakening dreams, the results were not affected either by the period of previous sleep (5, 6, 7, or 8 hours) or by the stage of sleep (stage 2 vs REM) (see Table 3). No differences were found between REM and NREM morning reports in the report length (that is, in the average of temporal units, in the percentage of multiunit reports, and in dream content). Only the spatiotemporal distortions and the uncertain reality testing were significantly more frequent in stage 2 than in REM dreams. Our expectations concerning a dream structure were not confirmed, as no differences were found between the narrative continuity of SO and that of morning reports. Regarding the dream content analysis (see Table 4), we found that many contents were significantly more frequent in the morning awakening dreams than in SO dreams: dreamer s presence (c 2 1=7.03, p<.01), laboratory references (c 2 1=5.37, p<.05), number of non-self characters (t 35 =4.32, p<.0001), the percentage of space-time distortions (c 2 1=10.78, p<.0001), bizarreness (c 2 1=23.23, p<.0001), and the mean number of emotions (t 35 =6.44; p<.0001). No differences were found in the intensity of the emotions (sleep onset mean=3.78; morning awakening mean=3.7). Concerning the awareness of the dreamer, we found that reality testing was maintained significantly more frequently in SO than in awakening dreams (c 2 1=8.64, p<.005), and more frequently lost in morning awakening than in SO dreams (c 2 1=10.87, p<.001). Results concerning the Self Scale showed a significantly higher percentage of point III (static representation of oneself) in SO dreams compared to awakening dreams (SO=13.70%, awakening = 1.30%; c 2 1=8.48; p<.005), and a significantly higher percentage of point V (precise awareness of one s mental and bodily self, similar to wakefulness) in awakening dreams compared to SO dreams (awakening=76.62%, SO=45.20%; c 2 =15.60; p<.0001). Analysis of the memory sources [ANOVA two-way: period of sleep (two levels) memory sources (three levels)] showed significant results. In particular, the analysis of the second factor (memory sources) was significant (F2,70=18.58; p<.0001): episodic memories were more numerous than semantic memories (p<.0001) (Scheffé test). This was true both for sleep onset (p<.0001) and morning awakening (p<.01) (Scheffé test) (see Table 5). The interaction between the two factors did not produce significant results. With the data on the temporal dating of the episodic memory sources, a second two-way analysis of variance was computed [phase of sleep (two levels) memory sources (four levels)]. The analysis of the second factor (temporal dating) proved significant (F3,105=70.57; p<.0001). Day residues (SO=57.46%; awakening=47.99%) and recent events (SO=36.59%; awakening=42.78%) in particular, were significantly more numerous than past events (SO=1.73%; awakening=3.62%) and prospective events (SO=4.22%; awakening=5.61%) in both sleep phases (Scheffé test; p<.0001). Moreover, day residues were 466

6 Table 3. Comparison between REM and stage 2 awakening dream reports. Morning Awakenings REM St 2 Temporal units (Mean) Multi-unit reports 100% 93.88% Narrative continuity 73.68% 67.39% Self 94.74% 97.96% Setting 94.73% 91.83% Lab references 26.31% 20.41% N. non-self characters (Mean) Dimensional distortions 10.53% 20.41% Space-time distortions* 10.53% 42.86% Implausibility 84.21% 79.59% Body feelings 21.05% 10.20% Emotions Reality testing: a) maintained 5.26% 10.20% Reality testing: b) uncertain* 10.53% --- Reality testing: c) lost 84.21% 89.80% * p<.01 Table 4. Comparison between sleep onset and awakening dream reports. Sleep Onset Morning Awakening Narrative continuity 83.72% 70.59% Self* 81.94% 95.83% Setting 86.11% 91.66% Lab references* 8.33% 22.22% N. non-self characters* Dimensional distortions 9.72% 19.44% Space-time distortions* 9.72% 31.94% Bizarreness* 43.06% Body feelings 8.33% 12.50% Emotions* Reality testing: a) maintained* 13.88% 1.39% Reality testing: b) uncertain 20.08% 9.72 Reality testing: c) lost* 65.28% 88.89% * p<.01 Table 5. Mean percentages of episodic, abstract self-referred, and semantic dream sources for sleep onset and awakening dream reports. Episodic Self-referred Semantic SO 47.43% 33.32% 19.25% Awakening 43.70% 32.01% 24.28% only significantly higher than recent events (p<.05) in sleep onset. Finally, the set of results was not affected by the order of the experimental nights (first vs second night). CONCLUSION The physiologic data which have emerged from this study are consistent with the normative data discussed in the introduction. Awakening takes place in REM about in 30% of cases and in NREM in 70%, with a clear prevalence of stage 2. We could conclude that the REM phase, which some authors have proposed as a time event intended to facilitate the transition into awakening, does not play an important role in normal conditions in regulating spontaneous morning awakening. The stage in which awakening occurs does not seem to be influenced by the duration of the period of sleep: we found no correlation in our study between these two variables, except in those few instances where awakening occurred in SWS, preceded by a longer period of sleep (stages 1-2: TST=350 minutes; REM: TST=360 minutes; SWS: TST=440 minutes). This confirms the unimportance of ultradian rhythmicity and the importance of circadian rhythmicity in determining the time of awakening, with respect to the parameters considered and in the absence of contradictory results. As far as mental experiences are concerned, the most interesting result is the considerable uniformity of the morning awakening dream reports, regardless of the stage in which the awakening took place. The only differences between the morning awakening dreams of REM and NREM (stage 1 or 2) were in the spatiotemporal distortions and in the uncertain reality testing results. Spatiotemporal distortions are a specific characteristic of bizarreness which concern the construction of the dream, and which we found to be more frequent in stage 2 awakenings. From the information-processing point of view, this result is difficult to explain, if we consider that global bizarreness (which includes formal, logical, and physical distortions) produced analogous results in all cases. We are unable to explain the concentration of errors in the spatiotemporal details in stage 2, such as the fusing of different places, impossible or incongruous spaces and times. Further research will be needed to establish whether this is stable evidence. There was also a marginal difference in awareness between the various stages of morning awakening. In general, reality testing is nearly always lost both in REM and NREM (84.20% and 89.80%). In REM sleep, however, in cases where mentation is not so clearly dreamlike, reality testing can be uncertain, whereas it is sometimes maintained in light sleep, as if recovery of waking awareness was anticipated. All other characteristics of the dreams reports are alike, as are the mnemonic sources of the dream production. This 467

7 would appear to provide initial support for the hypothesis that it is the transition from sleep to wakefulness which influences the dreaming preceding morning spontaneous awakening, rather than the sleep stage in which the dreaming occurs. To conclude, then, the stage-dependency hypothesis does not adequately account for the morning awakening dream experiences and their memory sources. We must now consider the differences between sleeponset and sleep-offset mental experiences. Comparison between the two psychophysiologic conditions produced many more differences than previous data led us to expect. It seems that the transitional nature that characterizes these two moments of sleep is not enough to produce the uniform features of the dreams, given the different psychological situations in which they occur. The results must be interpreted by taking into account the direction of the transition, (ie, the influence of both the preceding psychophysiological condition [wakefulness for SO, sleep for morning awakening] and the one that is to follow [sleep for SO, wakefulness for the ending of sleep]). The significant distinguishing characteristics between SO and morning-awakening dreams are the loss of reality testing and as far as the specific dream content is concerned the presence of self and other characters, lab references, bizarreness, and emotions. All these values are higher in the dreams of morning awakening than in SO. Furthermore, self representation more frequently makes use of a strong hallucinatory mechanism in awakening than in SO, which produces a subjective effect similar to the usual self-awareness during wakefulness. These differences can be interpreted as the expression of the more dreamlike characterization which takes place during the end of sleep. The influence of the preceding condition seems to be clear in this phase. The mental apparatus is still marked by an intense hallucinatory production of oneiric events, which are homogeneous with the dreams of the second part of the night. All the data produced by our study supports this view, such as the bizarreness, which is a typical dreamlike characteristic. We attribute the high levels of emotion during sleep offset both to the lingering effects of the previous emotional dreamlike experiences and to an emotion-charged expectation of the waking period which is to follow. Evidently, even if we accept that dreams serve the purpose of metabolizing the emotions accumulated during the day, this does not mean that their presence is reduced in every dream, particularly during sleep-offset, but that the emotions are probably more coherently organized within the economy of the dreamer s mind. The laboratory references found in the morning awakening dream experiences are probably due to a preparation for the day to come based on the last distinctive reference of the preceding day. The condition of SO shows markedly fewer dreamlike characteristics than the ending of sleep, as if the production of a typical oneiric product was more difficult. During SO, too, the direction of the transitional condition plays an important role. When the subject is starting from a condition of controlled wakefulness, still goal-oriented and/or solving-oriented, sleep onset can have characteristics which are more or less distinct from a more advanced dream experience. The gradual loss of consciousness, the loss of contact with reality, and the loss of thought control involve a series of sensory and cognitive steps: first wakeful thought, and then the appearance of mental intrusions and hypnagogic hallucinations, with an inefficient attempt to maintain a thoughtlike continuity. Only later will the first really dreamlike experiences appear. We report here an example of a typical sequence of mental experiences during an experimental awakening, carried out in the lab 3 minutes after the appearance of the first sleep spindles in descending stage 2: a metal object of uneven shape it was a triangular one... a razor blade, which stood out slightly, almost bent... two pieces of metal being rubbed together... a flash of color, seemed to be cloth maybe blue, or sky blue... a fraction made of two cubes, one of these had a door in it, which was open... I pushed my way in, I saw a van carrying food with a lot of shelves... a hospital corridor, a ward where I m internal, white coats, a huge person who came up to me, very likable, with normal clothes on... (the dream continues for some time). This example shows a typical experience: after a rapid succession of static and disconnected images, the experience assumes a hallucinatory dreamlike characteristic just at the moment in which the two cubes are opened and the dreamer, who was before only a passive spectator, penetrates into them and enters into the scene : the dream which follows is similar in its structure and organization to the dreams typically collected during more advanced sleep periods. The attempt to maintain contact with the external reality during sleep onset is in contrast with the need for sleep. This is a kind of psychophysiologic conflict, which could perhaps explain some characteristics of primary insomnia. It may be assumed that the sleep onset process gradually substitutes a physical reality with a different hallucinatory reality: in other words, a possible world with another possible world.* However, the condition of the morning awakening could also be described in terms of a psychophysiologic conflict between the need to wake up, on the one hand, and the contact with the hallucinatory world, on the other. * One offering has the world dividing every infinitestimal fraction of a second into an infinite number of possible versions, constantly branching and proliferating, with consciousness neatly picking its way through to create the illusion of a stable reality. (McEwan, 43, p.117) 468

8 Usually, however, the psychophysiological conflict of the morning awakening does not produce the distressing situation, which can be frequent during psychophysiological conflict at sleep onset. The principal similarity between the two sleep conditions is the same availability of the mnemonic sources involved in the dream production. This result appears to be specifically related to the transitional nature between conditions of vigilance that the two sleep phases share, rather than to the direction in which this transition takes place. In both situations, the ties with concrete experiences of wakefulness are important in activating dream content which is prevalently episodic memories, related to events from the dreamer s daily life; recent events are more prevalent than remote ones. Contrary to our expectations, however, events related to the day that was to follow (prospective memories) were only marginally active in influencing the dreams before morning awakening. This may be due to a laboratory effect, given that our subjects only agreed to come into the laboratory if they had no important commitments the following day; thus they will only have been utilizing routine events during the production of their dreams. On the other hand, not only did routine events have little emotional weight, but they were frequently kept in the memory as generalized (semanticized) events and were therefore deprived of any temporal connotation which might mark them as episodic content. These circumstances could also explain the minor importance of episodes from the following day in the morning dreams of our experimental sample. To conclude, our data appear to confirm the importance of the transitional condition in the production of both sleeponset and sleep-offset mental experiences. It appears above all to be the direction of such transition which influences the characteristics of the related dreams. 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