Investigating the effect of a nap following experimental trauma on analogue PTSD symptoms

Abstract

Cognitive models assume that the incomplete integration of a traumatic experience into the autobiographical memory results in typical symptoms associated with post-traumatic stress disorder (PTSD) such as intrusive re-experiencing. Sleep supports the integration of new experiences into existing memory networks through memory consolidation. In fifty-six females, we investigated whether a 90-min daytime nap (n = 33) compared to a wake period (n = 23) after being exposed to an experimental trauma (i.e. a trauma film) prevents PTSD analogue symptoms. Intrusive memories were recorded for seven days using a diary, overall PTSD symptoms were assessed using the Impact of Event Scale (IES-R) and affective response to trauma cues were measured one week after experimental trauma. The two groups did not differ in any of the analogue PTSD symptoms. However, participants obtaining rapid eye movement (REM) sleep in the nap experienced less distressing intrusive memories. Moreover, the duration of REM sleep and slow wave activity was negatively correlated with analogue PTSD symptoms. Our findings suggest that even a short sleep period after experimental trauma can play a protective role in trauma memory formation but only if the nap contains REM sleep. Our data provide additional evidence for a critical role of REM sleep in PTSD development.

Figure 1

Flow chart of sample size reduction.

Figure 2

Experimental procedure. In session 1 (T1), participants were exposed to a neutral and a traumatic film. Thereafter, half of the participants were allowed to take a 90-min nap while the other half stayed awake. Before and after each of these films, participants had to indicate their subjective mood, arousal as well as their current affective state. Electroencephalogram (EEG), electromyogram (EMG), electrooculogram (EOG) and electrocardiogram (ECG) were recorded during film viewing (in both groups) and during subsequent sleep (in the nap group only). EEG was recorded from Fz, Cz, Pz, Oz, C3, and C4 (according to the International 10–20 System, referenced to Cz). At the end of T1, participants received the intrusion diary and were asked to fill it in for the following seven days (number of intrusions). During T2, participants were exposed to trauma and neutral film cues, i.e. single pictures taken from the traumatic and the neutral film (i.e. trauma trigger task). ECG as well as subjective measures of mood, arousal and affective state were assessed before and after the trauma trigger task to indicate emotional response toward the film cues. Our main outcomes for the analogue intrusions were (1) number of intrusions (measured by the diary), (2) Distress associated with intrusions (diary) and (3) overall posttraumatic symptom score (IES-R). Further outcomes were the individual change of (4) mood, (5) arousal, (6) heart rate and (7) negative affect in response to trauma cues at T2.

Figure 3

Association between sleep and the processing of an analogue trauma. The amount of REM sleep in minutes (a) as well as EEG activity in the slow wave frequency band (b) were negatively correlated with the subjective distress induced by reported intrusions. (c) There was a tendency for a negative correlation between EEG activity in the theta band (i.e. 5–8 Hz) and the number of intrusions as reported in the intrusion diary cumulative over seven days post experimental trauma. *Significance after Šidák correction; #signifies marginal significance.

Figure 4

The processing of an analogue trauma in REM, noREM and wake group. The three groups did not differ regarding the number of intrusions as reported in the intrusion diary (a). A significant difference (*p < 0.05; **p < 0.01) between REM and noREM was found for subjective distress induced by reported intrusions. The REM group reported a lower level of distress after trauma film exposure as compared to the noREM and the wake group (b). The increase in negative mood in response to trauma film cues at T2 was marginally lower (^#p < .1) in the REM and noREM group as compared to the wake group (c).