Sleep-Wake Disorders

Reduced Vagal Activity in REM Sleep May Contribute to Impaired Fear Extinction

Jessica Nye, PhD
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PTSD-illustration
In order to relate vagal activity during sleep with extinction memory in the setting of PTSD, investigators at Massachusetts General Hospital recruited patients with PTSD and trauma-exposed controls for this study.

In posttraumatic stress disorder (PTSD), vagal activity during rapid eye movement (REM) sleep, which is involved with the consolidation of extinction memory, may be impaired, according to results of a study presented at the 36th Annual Meeting SLEEP 2022, held from June 4 to 8, 2022 in Charlotte, North Carolina.

One of the hallmarks of PTSD is impaired fear extinction memory and as REM sleep facilitates consolidation of fear extinction, abnormal sleep physiology may contribute to the persistence of PTSD-associated fear extinction. Recent studies have found evidence that vagal activity supports memory benefit of sleep and another study found lower vagal activity during sleep among patients with PTSD.

In order to relate vagal activity during sleep with extinction memory in the setting of PTSD, investigators at Massachusetts General Hospital recruited patients with PTSD (n=20) and trauma-exposed controls (TECs; n=37) for this study. All participants underwent 3 nights of ambulatory polysomnography with electrocardiogram followed by a fear conditional and extinction learning experiment and a consolidation PSG night. At 24 hours after the consolidation night, the participants underwent extinction recall testing.

Fear conditioning comprised mild electric shock using a conditioned skin conductance response (SCR) to an image of a colored lamp with a partial reinforcement approach which immediately extinguished the shock after an unreinforced presentation. Extinction recall was defined as the degree to which SCR remained suppressed at 24 hours.

In TECs, extinction recall significantly correlated with heart rate variability measures during REM sleep. Specifically with high frequency absolute power (Rs, 0.51; P =.009), high frequency normalized units (Rs, 0.54; P =.005), and root mean square of successive differences between normal heartbeats (Rs, 0.40; P =.046).

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In a regression analysis using extinction recall as the dependent variable, a significant proportion of the variance in REM sleep percentage, REM density, average duration of REM epochs, and N3 sleep percentage was explained by high frequency absolute power (R2, 0.50; P =.04).

These trends were not observed among the PTSD cohort.

This study was limited by its small sample size; however, this analysis was preliminary, and the entire sample size of the final study will comprise 70 patients with PTSD and 69 TECs.

The study authors concluded, “Our preliminary results suggest that vagal activity during REM sleep is involved in the consolidation of extinction memory and that this mechanism may be impaired in PTSD.”

Reference

Yuksel C, Watford L, Mendelsohn AK, Oliver K, Martinez U Pace-Schott E. Vagal activity in REM sleep is associated with extinction recall in trauma exposed individuals but not in individuals with posttraumatic stress disorder. Presented at SLEEP 2022; June 4-8; Charlotte, North Carolina. Abstract 675.