Sleep Disturbances do not Interfere with Emotional Memory Consolidation in Patients Diagnosed with PTSD
Internship report
Author: Mitja Seibold - 11383232 Research Master Psychology
University of Amsterdam
February - July 2017
Abstract
Sleep is a key factor for memory consolidation that also includes emotional memory. A hallmark of patients diagnosed with PTSD are sleep disturbances. Especially more stage 1 (N1) and less Slow wave sleep (SWS) are usually observed and might have a negative impact on memory consolidation. In addition, negative emotion should elevate sleep disturbances in these patients because of their problems with emotion regulation. In this presented experiment patients diagnosed with PTSD (N = 14) and a non-PTSD traumatized control group (N = 14) watched in one session an emotional distressing film fragment while in another session a neutral film fragment. In each session
questions concerning the observed film fragment were used to test memory immediately after watching the film fragment and after a whole night of undisturbed sleep (24 hours after the first memory test). Contrary to our hypothesis, results show no difference in memory performance between sessions or groups after sleep although analysis of sleep physiology indicates a significant increase in N1 and a decrease in SWS in PTSD
patients. Analysis of mood shows an increase in negative emotion in PTSD patients after watching the emotional disturbing film fragment compared to the control group.
However, this effect diminished again after a night of sleep indicating the possible effect of sleep on emotion regulation. Overall, the findings suggest that the observed sleep
disturbances in the PTSD group seem not to affect their memory performance. Limitation of this experiment and further
INTRODUCTION
Sleep is a key factor for memory consolidation (Stickgold, 2005; Diekelmann & Born, 2010) and also includes emotional memory (Wagner et al. 2006; Hu et al., 2006). During sleep a new encoded memory trace gets reactivated in the hippocampus and stored in neocortical structures (Gais et al., 2007). Thus, when we sleep the new memory trace get strengthened and protected against interference (Diekelmann et al. 2011). A stable and restorative sleep benefits memory consolidation (Rasch & Born, 2013) and contributes to emotion regulation (Mauss, Troy & LeBourgeois, 2013). On the contrary, stress as well as a traumatic event can lead to sleep disturbances (Kim et al. 2007, Babson et al. 2010), a disrupted or fragmented sleep, as well as sleep deprivation. That in turn can have a negative effect on the consolidation of a memory trace (Yoo et al., 2007; Van der Werf, 2009).
According to the Diagnostic and Statistical Manual for Mental Disorders (DSM-V (2013), American Psychiatric Association), subjective sleep disturbances and nightmares are one of the hallmarks of patients diagnosed with post-traumatic stress disorders (PTSD). However, research on sleep disturbances and PTSD found contradicting results. Some studies indicated that PTSD patients do not suffer from sleep abnormalities (Breslau et al., 2004, Fuller et al., 1994), while others found that PTSD positively correlate with sleep disturbances (Germain & Nielson, 2003, Lavie et al., 1998, Mellman et al., 1997).
These disturbances include problems falling asleep, fragmented sleep and multiple awakenings during the night (Germain,
2013). The results of a meta-analysis indicate that in general patients with PTSD suffer from sleep disturbances including
more stage 1 (N1) sleep and less slow wave sleep (SWS) (Kobayashi, Boarts & Delahnty, 2007).
In addition, most of the included studies found greater rapid eye movement (REM)-density compared to non-PTSD patients. The results of another study that investigated REM-sleep
disturbance in PTSD-patients conclude that PTSD patients had more REM to wake and more REM to stage 1 transitions
(Spoormaker & Montgomery, 2008). Furthermore, the authors found more REM periods in PTSD patients. However, these REM periods were of shorter duration compared to normal REM periods. Concluding that not only subjective but also
objective sleep disturbances could be considered a hallmark of PTSD and that sleep disturbances influence memory
consolidation during sleep one can assume that patients diagnosed with PTSD also suffer from reduced memory consolidation (Van Liempt et al. 2011).
A study by Lipinska, Timol, Kaminer and Thomas (2013) could show, that lower retention performance for a declarative memory task correlated with decreased amount of REM sleep. A study by Geuze et al. (2009) indicated that PTSD leads to problems in figurative, logic and verbal memory. All these findings suggest that sleep disturbances in patients diagnosed with PTSD have a negative impact on declarative memory
performance.
Whether the same effect occurs in emotional memory
consolidation is unknown. In a previous study with healthy participants, Talamini, Bringmann, de Boer and Hofman (2013) examined the effect of an emotional distressing film fragment on sleep. In this study, participants watched an emotionally neutral film fragment in one session and an emotional
distressing film fragment in a second session. Undisturbed sleep was recorded for the whole night that followed each
session. Participants had to perform a retrieval test
immediately after the film fragment as well as after a night of sleep (however 24 hours after the first retrieval test). The behavioural results showed no difference between neutral and emotional memory performance before and after sleep. Nevertheless, the authors found an effect in the underlying sleep physiology. Compared to neutral memory consolidation, emotional memory consolidation led to an increase in SWS, an altered pattern in REM-sleep and sleep deterioration. This indicated an inherent relation between emotion regulation and sleep physiology.
Compared to healthy participant research suggests that emotional memory consolidation in PTSD patients differs in numerous ways. Patients diagnosed with PTSD have a smaller right hippocampal volume that correlates with decreased short term memory (Douglas, 1995). In addition, these patients have an elevated cortisol level that links to changes in arousal level (Baker et al., 2005) as well as functional alteration in specific cortical and subcortical brain areas involved in
emotional memory including the amygdala (Rausch et al., 1996, Bremner et al., 1999). PTSD patients are more sensitive to loud noises (Orr, Lasko, Shalev & Pitman, 1995) and show an elevated conditioned fear response (Grillon & Morgan, 1999). Furthermore, these patients have problems with emotion
regulation (Ehring & Quack, 2010) that might impact emotional memory consolidation.
In conclusion, it seems that patients with PTSD differ in their ability to consolidate memory compared to non-PTSD patients especially because of occurring disturbances during sleep. The aim of this study is to examine the differences in
emotional and neutral memory consolidation and the effect of sleep in patients diagnosed with PTSD and a non-PTSD
traumatized control group. Furthermore, the effect on emotion regulation and sleep physiology is observed. As in the study by Talamini et al. (2013) both groups watched an emotionally neutral film fragment (from now on called neutral film
fragment) as well as an emotional disturbing film fragment (from now on called emotional film fragment). After watching each film fragment memory retrieval was tested and followed by a full night of undisturbed sleep. Twenty four hours after the initial memory test, an additional memory retrieval test on film cues was assessed.
Because of the prediction of sleep disturbances in the PTSD group it is expected to find a difference in sleep physiology between the PTSD and the control group. Furthermore, it is expected that the emotional film fragment induces sleep
disturbances in the PTSD group that negatively influences the memory consolidation during the night and thus the memory retrieval the following day. Therefore, the sleep physiology should differ significantly after the emotional film fragment compared to the neutral film fragment in the PTSD group as well as between the PTSD and the control group (Hypothesis 1). Furthermore, because of the expected sleep disturbances the memory retrieval performance in the emotional film session should therefore be degraded compared to the neutral film session in the PTSD group as well as compared to the control group (Hypothesis 2). In addition, as mentioned above, PTSD patients have problems with emotion regulation. Sleep on the other hand facilitates emotion regulation. It is therefore expected that the negative mood induced by the emotional film fragment (Day 1) stays elevated even after sleep (Day 2) in PTSD patients compared to the neutral film session and the
control group due to the expected sleep disturbances (Hypothesis 3).
MATERIALS AND METHODS
Ethics statement. All participants provided written informed consent. The study was approved by the ethics committee of the University of Amsterdam.
Participants. Thirty-two participants took part in the study. Eighteen (1 female, 17 male; mean age: 43.89 years, SD = 8.35) of these participants were patients diagnosed with PTSD
according to DSM-V criteria and were assessed through the Clinical Administered PTSD Scale (CAPS - higher than 50 to be eligible for trauma-focused psychotherapy; Blake et al.,
1995). The other 14 participants (1 female, 13 male; mean age: 44.50 years, SD = 7.07) were not diagnosed with PTSD (CAPS score lower than 10) and thus assigned to the control group. However, they had experienced a trauma (according to the DSM-V criteria) at some point in their lives. All participants were either army veterans or (ex-)police officers and had not seen the films used as stimuli prior to the experiment. Subjects were encouraged to have a regular bedtime schedule at least three days prior to the start of the experiment and refrain from alcohol and medication. All subjects had to be between 18 and 65 years of age and no acute suicidality nor presence of psychotic disorder, bipolar disorder, depression with
psychotic features or substance related disorders over the three months prior to the experiment. Furthermore,
participants had no history of sleep disorders, or an atypical sleep pattern with less than 6 hours sleep per night. For the
PTSD group all exclusion criteria applied only prior to PTSD onset.
All patients diagnosed with PTSD were recruited from the
Foundation Centrum ’45 and Psychotrauma Diagnosis Centre, part of Arq Psychotrauma Expert Group. Of note, this centre is
specialized in patients that experienced a severe traumatic event. Hence, all of the PTSD patients suffered from a severe form of PTSD (CAPS mean score of 80). All patients were tested before the onset of treatment. The control group (non-PTSD trauma patients) were recruited through advertisements. Both groups were matched on age, gender, education level and
occupation. During the experiment seven participants diagnosed with PTSD were on medication that could not be interrupted. Patients were not excluded because of their medication intake. Four of these participants were using SSRI’s (Paroxetine,
Venlafaxine, Sertraline, Citalopram). One participant was using an antipsychotic (Chlorprothixene) as well as an
antidepressant (Mirtazapine). Furthermore, three participants were using sedatives or hypnotics (Lormetazepam, Zopiclon or melatonin). Overall, four participants of the PTSD patients had to be excluded from the analysis because of recording
problems. Thus, 14 participants in the experimental as well as 14 participants in the control group were used for the
statistical analysis.
Stimuli. Two film fragments (neutral and emotional) were used in this study to induce emotional memory consolidation as well as neutral memory consolidation. Emotional film fragments are commonly used in research to induce emotional arousal and
valence as well as to compare them to the neutral state (e.g., Cahil et al., 1996, Talamini et al., 2013). The emotional film fragment was an excerpt from the movie “The Passion of the
Christ” (Directed by Mel Gibson, 2004). It showed a torture scene. The neutral film fragment was an excerpt from the
documentary “March of the Penguins” (Directed by Luc Jacquet, 2005). It showed the hatching of Emperor Penguins in the
Antarctic. Each film excerpt was presented for 10 minutes. The memory test consisted of presenting 6 stills of the movie
scene (each presented for 1 second with a 9 second
inter-stimulus interval) to reactivate memory. This was followed by eleven multiple choice questions on the content (visual and auditory, perceptual and conceptual as well as central and peripheral aspects) of the film. In each question participants had the opportunity to choose between four
answers including an “I don’t know” option (participants were encouraged not to guess). Two versions of memory test for each film fragment were used so that the questions differed between Day 1 and Day 2 memory retrieval. The mood states were
assessed through a shortened Dutch version of the Profile of Mood States (POMS, Shacham, 1983). As in the previous study (Talamini et al. 2013) only three of the mood states were assessed by using the depression, anger and tension scale. Furthermore, participants used a “global mood scale” (from 1 - very positive mood till 9 - very negative mood) to indicate their general mood and the Stanford Sleepiness Scale (Hoddes et al., 1973) to assess sleepiness.
Polysomnographic recordings. Polysomnographic measures were recorded with a portable 16-channel amplifier (TMS-i) and the Galaxy recording and analysis software (PHI-International). For electroencephalography (EEG) 4 channels (F3, F4, C4, O2, referenced to linked mastoids) were used. Additionally
electrooculography (EOG) and electromyography (EMG) with two electrodes respectively, as well as ECG for monitoring heart
rate and plethysmography monitoring blood oxygenation were recorded. The sampling rate was 512 Hz.
Procedure. The experiment consisted of two identical sessions (except for the different film fragment) with a break of a week in between. One session consisted of two days. On day 1 the experiment started at around 10 pm. First, participants’ mood and sleepiness were assessed via the aforementioned questionnaires. Next, one of the film fragments (one session emotional film fragment and the other session neutral film fragment; counterbalanced) was presented, immediately followed by the aforementioned memory test and questionnaires. At
around 11 pm participants went to bed for a full night (~ 8 hours) of undisturbed sleep with polysomnographic measures. Twenty-four hours after (day 2) the first test, participants had a retest, consisting of the same questionnaires as on the previous day for sleepiness and state of mood; however to test memory after sleep different questions were used (compared to day 1).
Data analysis. Polysomnographic recordings were scored
according to the guidelines of the American Academy of Sleep Medicine (AASM; Iber et al., 2007). For each participant we calculated the Total Sleep Time (TST), Wake Before Sleep Onset (WBSO), Wake After Sleep Onset (WASO) and standard sleep
stages (N1, N2, SWS, REM) as well as SWS/REM-latency, REM-episodes and REM-fragmentation. The definition of
REM-fragmentation was as follows: (1) An interruption of the REM period by any sleep stage (2) of equal or less than 5 minutes. An interruption longer than 5 minutes indicates
(2013), the sleep physiology in the first half of the night with the second half of the night was compared.
For the memory score the score for each memory performance; that is for each session (emotional film fragment versus neutral film fragment) before and after sleep as well as
between the groups (PTSD versus control group) was calculated. The total score of correct answers were compared.
As mentioned above the analysis focused on the three subscales “Depression”, “Anger” and “Tension” of the POMS. The POMS
questionnaire was used at four time points (T1: baseline - prior watching film fragment; T2: post watching film fragment; T3: after the night of sleep (Day 2); T4: after the memory recall (Day 2))to investigate the effects of the different film fragments and the night of sleep.
Due to the small sample size there was no normality in
specific subgroups. However, a general linear model was fitted and this indicated that we can assume normality given a bigger sample. Thus, a repeated measure ANOVA was chosen.
For all confirmatory analysis a Group (PTSD, Control) x Session (emotional film fragment, neutral film fragment) ANOVA, or Group x Session x Time (T1, T2, T3, T4) repeated measure ANOVA was used, when the variables confirmed the
necessary pre-assumptions (e.g. normal distribution). For post hoc analysis t-tests were used with Bonferroni Correction if applicable. For non-Gaussian variables a Whitney-U test
(independent sample) or a Wilcoxon Signed Rank test (paired sample) was used.
For exploratory analysis the Pearson’s Correlation Coefficient was calculated. The α-level was set to 0.05. Outliers were data points that exceeded three standard deviations. These outliers were not removed but were set to the score of the three standard deviations. Furthermore, the effect size
Cohen’s d is reported. For statistical analysis the
statistical software R (Ihaka & Gentleman, 1996) was used.
RESULTS
Memory performance. Memory was tested before and after sleep because of interest in the effect of sleep on memory
performance after watching an emotional arousing film compared to a neutral film, as well as between patients diagnosed with PTSD and a control group.
Table 1
Mean correct score of memory performance pre/post sleep
Pre-Sleep Post-Sleep
Emotional Neutral Emotional Neutral
Group mean sd mean sd mean sd mean sd
PTSD 5.29 (1.64) 4.57 (1.74) 4.57 (1.95) 3.71 (1.49)
CONTROL 6.36* (2.24) 4.5 (1.51) 5.79 (2.19) 4.64 (1.22) * p < .05 between emotional and neutral session in the control group.
As summarized in Table 1 as well as in Figure 1 memory content after watching the emotional film fragment was remembered
better than after the neutral film fragment (main effect for Session: F(1,26) = 9.717, p = .004, CI[0.38,1.98], d = 1.18). However, post hoc analysis revealed that this effect only reached significance in the pre sleep memory performance of the control group (t(13) = -2.378, p = .017, CI [-3.32, -0.39], d = -1.04). Overall, there was no statistical
significant difference in the pre sleep and post sleep memory performance (interaction effect between Group (PTSD, control),
Session (emotional, neutral) and Time (pre sleep, post sleep): F(1,26) = 0.654, p = .426, CI[-0.44,1.05], d = 0.31). In
summary, before sleep the emotional film fragment lead to an increase in memory performance in the control group. The night of sleep had no significant impact on the memory performance, neither for the PTSD group or the control group. This was
regardless of the film fragment they watched the night before.
Figure 1 Mean memory score for each group (PTSD versus
Control) and session ([emo]tional versus [neu]tral). Pre-sleep as well as post-sleep scores are represented. Error bars
indicate the standard error. * indicates p < .05.
Sleep physiology. Because we assumed that the emotional film fragment affects the sleep physiology, that in turn affects the memory performance, we analyzed the sleep architecture for both sessions and groups (ANOVA with factor Session and
Group). In Appendix A an overview can be found of the sleep stages for the whole night as well as for the first and second half of the night respectively. Analysis of the full night revealed only a significant difference in N1 (Main effect for
group: F(1,24) = 5.03, p = .034, CI[0.07, 1.69], d = 0.88; Interaction effect: F(1,24) = 10.229, p = .004, CI[0.41, 2.10], d = 1.26) and a trend effect in SWS (Main effect for group: F(1,24) = 3.969, p = .058, CI[-0.02, 1.58], d = 0.78). The PTSD group had more N1 sleep in both film sessions
compared to the control group (emotional: t(21.6) = 3.037, p = .006, CI[0.36, 2.03], d = 1.19, neutral: t(11) = 3.592, p = .004, CI[0.55, 2.27], d = 1.41). The control group had
significantly more SWS-sleep after watching the neutral film compared to the PTSD group (t(23.12) = -3.958, p = .001, CI[-2.44, -0.68], d = -1.56). This effect was not found after watching the emotional film fragment (p = .118).
The analysis of the first and second half of the night revealed more specific changes in the sleep architecture.
Between the two groups the PTSD group had more N1 in the first half of the night compared to the control group - however only in the emotional film session (t(18.9) = 2.418, p = .026,
CI[0.14, 1.76], d = 0.95). Furthermore, the control group had more N1 in the neutral film session compared to the emotional film session (t(11) = 3.124, p = .010, CI[0.39, 2.07], d = 1.23).
In the second half of the night, the PTSD group had more N1 in the emotional film session compared to the control group
(t(22.04) = 2.373, p = .027, CI[0.12, 1.75], d = 0.93). In contrast, N2 and SWS was reduced for the PTSD group (compared to the control group) in the emotional session (N2: t(23.71) = -2.141, p = .042, CI[-1.65, -0.04], d = -0.84; SWS: t(12.25) = -3.058, p = .010, CI[-2.04, -0.37], d = -1.20).
The analysis of the REM latency revealed that the PTSD group needed longer than the control group in both sessions until they reached the first REM period (neutral: t(22.78) = 2.029, p = .054, CI[-0.003, 1.60], d = 0.80; emotional: t(17) =
1.839, p = .083, CI[-0.07, 1.52], d = 0.72). However, as
indicated by the p-value, this was only at trend level. There was no difference between groups or sessions for the SWS
latency.
The analysis of the number of REM-episodes revealed that the PTSD-group had less REM-episodes than the control group
(neutral: t(20.87) = -3.017, p = .007, CI[-2.02, -0.35], d = -1.19; emotional: t(23.70) = -2.309, p = .030, CI[-1.72,
-0.10], d = -0.91). There was no difference between the groups or sessions in REM-fragmentation (ps > .232).
Mood and sleepiness.
Depression Subscale. In the PTSD-group, watching the emotional film fragment led to a higher depressive mood afterwards(p = .014 between T1 and T2). However, this depressive mood
decreased after a full night of sleep and did not change after reactivating the memory (between T2 and T3: p = .007; T2
versus T4: p = .013). For the neutral film fragment analysis revealed that there was no significant difference in the PTSD group and thus indicates that the film fragment did not affect the depressive mood. Hence, for the PTSD group the emotional disturbing film fragment led to an increase in depressive mood (p = .001 at T2) but the reactivating of the memory a day
later had no impact anymore when comparing the emotional to the neutral session.
The emotional film fragment in the control group led not
immediately to an increase in depressive mood. Interestingly, after the night of sleep the depressive mood was significantly higher and stayed as high after reactivation of the memory (p = .012 between T1 and T3; p = .015 between T1 and T4).
We then compared the two groups on each individual time-point for each session. This revealed that in the emotional session
there was a significant difference between the two groups at T1 (p = .001) as well as T2 (p < .001) and T4 (p = .048). Hence, the PTSD group was more depressed before watching the film fragment compared to the control group. This difference in depressive mood increased after watching the film fragment. After a night of sleep the depressive mood did not differ
between the two groups until the reactivation of the emotional memory when the depressive mood increased again in the PTSD group, however not in the control group. A similar pattern can be observed in the neutral session. The two groups
significantly differed at T1 (p = .027) and T2 (p = .018). Thus, on average the depressive mood was again higher in the PTSD group before watching the film fragment and did not
change significantly before the night of sleep between the two groups. After a night of sleep the significant difference in depressive mood disappeared. Furthermore, there was no
significant difference between the two groups after reactivation of the memory.
Anger Subscale. We conducted the same post hoc analysis as for the depression scale. For the PTSD group in the emotional
session the anger score did change significantly between T1 and T2 (p = .022) and T2 and T3 (p = .043). Thus, similar to the depression scale, the emotional film fragment led to an increase in anger and decreased again after a night of sleep in the PTSD group. There was no significant difference between the time-points for the PTSD group in the neutral session. Furthermore, only in T2, thus immediately after watching the film fragment, a significant difference between the sessions for the PTSD group was observed (p = .009). Thus, in the PTSD group the emotional disturbing film fragment affected anger only immediately after watching the film compared to the neutral session. Again, similar to the depression score, for
the control group an increase in anger in the emotional
session was observed after a night of sleep (between T1/T2 and T3: ps < .050). However, this difference decreased again after memory reactivation (T3 versus T4: p = .020). For the neutral film session there was only a significant difference between T3 and T4 (p = .023). Thus, the anger score decreased after reactivation on the second day. The post hoc analysis between the two sessions in the control group on each time-point
revealed no significant difference between the two sessions at all four time-points. Similar to the depression scale the PTSD group had a higher anger scale before watching the emotional film fragment (T1: p = .002) until the next day (T2: p < .001). Twenty four hours later the groups did not differ any more, except after memory reactivation that led again to an increase in anger in the PTSD group (T4: p = .028). In the neutral session the PTSD group had an elevated anger score at T1 (p = .032) as well as at T4 (p = .041).
Tension Scale. For the PTSD group the emotional film led to an increase in tension (T1 versus T2: p = .010). This elevated mood decreased again after a night of sleep (T2 versus T3: p = .010; T2 versus T4: p = .023). There was no significant
difference for the PTSD group between the time-points in the neutral session.
Similar to the two other mood scales in the emotional film session, for the control group the tension increased not
immediately after watching the film fragment but after a night of sleep (Difference between T1/T2 and T3/T4: ps < .044).
In the neutral session similar to the emotional session the tension was higher after the night of sleep (T1/T2 versus
T3/T4: ps < .008). There was no significant difference between the two sessions in each time-point. The comparison between the two groups in the emotional session as well as in the
neutral session indicated that the tension was higher in the PTSD group - however only before going to bed (T1/T2: ps < .002).
Sleep-quality analysis. Only in the neutral film fragment night was the sleep quality significant lower for the
PTSD-group compared to the control group (p < .001). There was no difference in the emotional film fragment night between the two groups.
Stanford Sleepiness Scale. The SSS indicates that the PTSD group generally felt more tired compared to the control group regardless of the session (ps < .033). However, this was not the case at T1, thus before watching the film fragment.
Exploratory analysis.
To get a more precise picture of the impact of the emotional arousing film fragment on the sleep physiology, additionally correlations for the emotional disturbing film session on the POMS’ score that was recorded immediately after watching the film fragment (T2) and the sleep architecture were calculated. PTSD Group. In the emotional session of the PTSD group a
significant negative correlation between the tension score and the amount of REM sleep (r = -.54, p = .047) as well as the TST (r = -.59, p = .026) were observed. Furthermore, the TST negatively correlated with the Depression scale (r = -.53, p = .050). Thus, the higher the mood of tension and depression the less the participants slept, with diminishing REM-sleep.
Additional significant correlations were only found in the second half of the night. There was a significant negative correlation between N2 and the tension scale (r = -.58, p = .028) as well as between WASO and the anger scale (r = -.59, p = .027) indicating that the less mood of tension and anger the
participants scored the more N2 and WASO was observed respectively.
Control Group. For the control group there was a significant positive correlation between N1 and the participants tension mood (r = .61, p = .033). Thus, the more tension participants felt the lighter they slept. As in the PTSD group, only in the second half of the night significant correlations with the POMS scores were observed. There was a significant positive correlation between N1 and the tension scale (r = .72, p = .009) and a positive trend between anger and N1 (r = .57, p = .052). This indicates that an elevated mood of tension and anger led to an increase in light sleep in the second half of the night.
DISCUSSION
Contrary to the second hypothesis there was no change in
memory performance due to the emotional film fragment and its possible effect on sleep disturbances in patients diagnosed with PTSD. In addition, there was no difference in memory
performance between the PTSD and the control group. The second hypothesis to observe a change in memory performance was
driven by the estimated effect of the emotional disturbing film fragment and its impact on sleep - indicated by occurring sleep disturbances (Hypothesis 1). The analysis of sleep
physiology, however, indicates a more general pattern between the PTSD group and the control group rather than between the emotional and neutral session. The PTSD group had more N1 sleep compared to the control group. This was observed for both sessions. The reduction of SWS for the PTSD group was only observed in the neutral session suggesting a possible
effect of the emotional film fragment on the amount of SWS in the control group. The analysis of the first half and second half of the night separately revealed additional findings. In the first as well as the second half of the night the PTSD group had more N1 in the emotional session. In the second half of the night N2 and SWS was reduced only for the PTSD group in the emotional session compared to the control group. As stated above, these last findings are in contrast to the full night analysis. Overall, the increase in N1 and decrease in SWS has been found in previous literature to be a marker for sleep disturbances in PTSD patients (Kobayashi et al., 2007). Thus, the results presented here indicate that these sleep
disturbances seem not to interfere with emotional memory
consolidation. Our results also indicate that in first half of the night, SWS, important for declarative memory consolidation (Diekelmann & Born, 2010), was not disrupted and did not
differ between the groups and sessions possibly resulting in the memory performance observed. Furthermore, no difference in REM sleep was observed another possible indicator of the
observed results in memory performance because previous
research suggested a relationship between REM sleep and memory performance in PTSD patients (Lipinska et al., 2014). That the analysis indicated an effect in prolonged REM-latency can be explained due to the fact that subjects in the PTSD group might have skipped the first REM-episode. However, until now, it is unknown what kind of effect the prolonged timing of the first REM-episode has on memory consolidation and should be subject for future studies. In our case, it seemed not to affect memory performance although previous research suggests that especially a shortened REM-latency is an indicator for emotional processing during sleep (Lauer et al. 1987).
However, this was tested in healthy subjects and might differ in patients diagnosed with PTSD.
Nevertheless, as Goerke, Müller, and Cohrs (2017) suggest, polysomnography might not be the perfect tool to adequately investigate sleep disturbances in PTSD patients. Thus, it is necessary to investigate the exact underlying mechanisms to clearly understand the function of sleep in memory processing in PTSD patients. Especially analyzing the underlying
oscillatory activity (e.g. frequency analysis of the theta and sigma band) during sleep after an emotional task has been
encoded, should give a more adequate insight into the effect of sleep disturbances in PTSD patients and its effect on memory consolidation (Nishida et al., 2008, VanderHeyden et al., 2015). The focus on REM sleep, REM sleep deprivation and its effect on memory consolidation in PTSD patients is
suggested because of the importance of REM-sleep for emotional memory consolidation and emotion regulation (Walker & van der Helm, 2009; Wagner, Gais & Born, 2001). This might also help to share light on the debate if sleep, sleep deprivation or only REM sleep deprivation (Arias, Delorme & Poe, 2016) is a more successful first aid tool to prevent the development of PTSD after the experience of a traumatic event.
Overall, the here presented results suggest that patients diagnosed with PTSD only differ in their amount of N1 sleep and SWS, and otherwise do not differ severely in their sleep physiology from non-PTSD but traumatized control subjects in a laboratory settings. This laboratory setting might be a key factor (Spoormaker & Montgomery, 2008) - as research has shown that nightmares are diminished in PTSD patients that sleep in a laboratory under supervision (Fisher et al. 1970; Woodward et al. 2000). Thus, this can also be suggested in this
because of a more secure environment in the sleep laboratory than at home. In addition, the emotional disturbing film fragment might be too shallow to successfully induce sleep disturbances in patients diagnosed with PTSD. These patients were police officers or soldiers that experienced a severe traumatic event leading to the diagnosis of PTSD. Hence, a film excerpt of a pre-medieval torture scene might not have been sufficient enough - especially watched in a secure environment such as a laboratory. Interestingly, in the control group watching the emotional film fragment led to a significant increase in memory performance before sleep. As previous literature has shown, memory with emotional content is remembered better than neutral memory in healthy subjects (Kensinger & Corkin, 2003). This effect was not found in the memory performance of the PTSD group and might indicate that memory encoding for emotional stimuli might be disturbed. An analysis of event related potentials at encoding stage for emotional and neutral stimuli between patients diagnosed with PTSD and a control group might help to understand the
underlying mechanism of emotional memory encoding in PTSD patients (Dolcos & Cabeza, 2002). However, as the POMS mood scales indicate the emotional film fragment had a significant impact on the mood of the PTSD patients. The increase in
negative mood correlating with decrease in amount of TST and REM sleep in the PTSD group and an increase in negative mood with N1 in the control group also indicates the effect of the emotional film fragment on sleep physiology. Interestingly, and contrary to the third hypotheses, the increase after watching the emotional film fragment in depression, tension and anger represented by the mood score decreased again after a night of sleep and stayed for most of the three mood scores at baseline level even after reactivation of the emotional
memory. This might indicate that sleep supports emotion regulation in PTSD patients if the severity of sleep
disturbances is limited. The results of the POMS scale of the control group shows a different pattern of emotion regulation. Instead of the expected increase in negative emotion
immediately after the emotional film fragment the negative emotion shifted and only increased after the night of sleep. Hence, it seems like that sleep facilitated negative emotion in this control group. However, for the control group this effect was also partially observed in the neutral film
session. This finding is contrary to previous research that showed that sleep facilitates emotion regulation, thus leading to a decrease in emotional arousal (Mauss et al., 2013).
However, mood after sleep was assessed 12 hours after patients woke up from the night of sleep. Therefore, explaining the results solely on the night of sleep should be treated with caution. Usually changes in sleep dependent memory
consolidation or emotion regulation is tested in the morning after the test night (e.g. Lipinska et al., 2014). This is done to prevent influence of awake dependent memory
consolidation and emotion regulation to affect the results. However, due to the fact that nocturnal neuroendocrine
processes differ during the night and also differ between 8pm and 8am (Born & Fehm, 2000), these processes might influence memory consolidation and emotion regulation (Payne & Nadel, 2004). Thus, it is reasonable in order to control for these hormonal effects to test the memory or mood state 24 hours after pre sleep testing.
Conclusion
In conclusion, this experiment indicates that patients diagnosed with PTSD do suffer from sleep disturbances,
however, these sleep disturbances do not seem to deteriorate memory performance. A follow up study with healthy subjects (without any trauma) with the same criteria as the control group might contribute to the understanding of the differences and similarities between patients diagnosed with PTSD, trauma control participants and healthy participants. It is suggested that the disturbances of the underlying sleep physiology plays a crucial part in the effect of memory performance and
treatment success (Stickgold & Manoach, 2017). Thus, reduced sleep disturbances, as observed in this presented study, increase the chance of normal memory performance. In
therapeutic sessions it is of importance to be aware of the memory capabilities of patients diagnosed with PTSD. Thus, to study the effect of memory consolidation, emotion regulation and sleep in these patients is of importance to facilitate the therapeutic success by attenuating the symptoms. The presented experiment is the first to directly analyze the effect of
sleep on memory consolidation and emotion regulation in PTSD patients compared to a non-PTSD trauma control group and
indicates that memory performance is not disrupted while sleep disturbances were observed. Thus, a therapeutic success in PTSD might lie in establishing a more secure sleep environment to diminish sleep disturbances in these patients so that they can benefit from successful memory consolidation and emotion regulation during the night for a better therapeutic success during the day.
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