Accumulating evidence suggests that rapid eye movement sleep (REM) supports the consolidation of extinction memory. REM is disrupted in PTSD, and REM abnormalities after traumatic events increase the risk of developing PTSD.  Therefore, it was hypothesized that abnormal REM in trauma-exposed individuals may pave the way for PTSD, by interfering with the processing of extinction memory. In addition, PTSD patients display reduced vagal activity. Vagal activity contributes to the strengthening of memories, including fear extinction memory, and recent studies show that the role of vagus in memory processing extends to memory consolidation during sleep. Therefore, it is plausible that reduced vagal activity during sleep in trauma-exposed individuals may be an additional mechanism that impairs extinction memory consolidation. However, to date, the contribution of sleep vagal activity to the consolidation of extinction memory or any emotional memory has not been investigated. To test these hypotheses, we examined the association of extinction memory with REM characteristics and REM vagal activity (indexed as high frequency heart rate variability; HF-HRV) in a large sample of trauma-exposed individuals (n=113). Consistent with our hypotheses, REM sleep characteristics (increased REM density and shortened REM latency) were associated with poorer physiological and explicit extinction memory. Furthermore, higher HF-HRV during REM was associated with better explicit extinction memory. These findings support the notion that disrupted REM may contribute to PTSD by impairing the consolidation of extinction memory and indicate the potential utility of interventions that target REM sleep characteristics and REM vagal activity in fear-related disorders.

REM Sleep Measures and REM Vagal Activity Predict Extinction Recall in Trauma-Exposed Individuals