Poor memory performance and REM sleep in PTSD
Both sleep abnormalities and cognitive impairment are common in people with post-traumatic stress disorder. In particular, patients often experience greater REM sleep fragmentation and REM-related arousals. Acknowledging the role that REM sleep plays in sleep-dependent memory consolidation, a recent study in the Journal of Sleep Research compared the sleep and memory profiles of three groups of participants: those with PTSD, those who had been trauma-exposed but did not develop PTSD, and healthy good sleepers.
All participants slept in the sleep laboratory for one night. Participants were trained and tested on two tasks prior to sleep – one involving reading passages and then being asked to recall the gist of the content (declarative memory task); and the other was a finger-tapping task, which involved learning a motor sequence (procedural memory task). Participants were then provided with an 8 hour sleep opportunity and re-tested on the same tasks in the morning. The primary variable of interest was change in task performance pre-to-post sleep (reflecting level of retention).
In general, the groups did not differ with respect to whole-night sleep architecture or continuity variables. However, when looking at the first and second half of the night, it was found that REM sleep was shorter and percentage of wakefulness was higher in the last half of the night in those with PTSD relative to the other two groups. Patients diagnosed with PTSD also retained significantly less information on the declarative memory task relative to healthy controls. Poorer memory performance in this group was correlated with lower amounts of time spent in REM sleep.
The authors make the case that sleep abnormalities in PTSD are not simply epiphenomenon but may have an important role in driving cognitive impairment:
“Our data suggest that, in PTSD, there are sleep-related deficits in memory consolidation. Furthermore, the data suggest that disrupted REM sleep is sufficient to produce these deficits. These data are consistent with extant literature suggesting that sleep benefits memory consolidation via predictable neurobiological mechanisms, and that REM disruption is more than merely a symptom of PTSD.”
Lipinska, M., Timol, R., Kaminer, D, Thomas, K.G. (2014). Disrupted rapid eye movement sleep predicts poor declarative memory performance in post-traumatic stress disorder. Journal of Sleep Research, doi: 10.1111/jsr.12122