New research from Rutgers University (NJ, USA) has demonstrated that sleep quality is associated with fear learning in young adults, and could be used as a predictor of susceptibility to PTSD.
Problems with sleep and PTSD are known to be common bedfellows, with REM sleep in particular associated with neural activity following fear conditioning.
While research has been conducted to understand how sleep quality affects established fear memories, studies investigating the effect of sleep patterns on fear memories prior to trauma are few and far between.
“These [previous] studies have been restricted to analyzing the effects of a single night of sleep –thus assuming a state-like relationship between the two,” explained the authors.
The new research used unobtrusive long-term monitoring tools and fMRI, monitoring both male and female students’ sleep for 1 week. This included a headband to measure brain waves, a bracelet to measure arm movements, and a sleep log. A neuroimaging experiment was then used that taught the students to associate a neutral image with a mild electric shock.
The team demonstrated that higher baseline levels of REM sleep phase were associated with weaker modulation of activity in, and connectivity between, the amygdala, hippocampus and ventromedial prefrontal cortex during fear learning. While Skin-Conductance-Responses were weakly associated with activity in the amygdala, there was no correlation with REM sleep, suggesting that REM modulates fear acquisition indirectly.
Results were replicated in a follow-up experiment using traditional polysomnographic monitoring of sleep during the night prior to fear learning.
These findings support the theory that REM sleep reduces norepinephrine levels, which could reduce sensitivity to fear stimuli.
“Specifically, the results of this study suggest that baseline REM sleep may serve a protective function against enhanced fear encoding through the modulation of connectivity between the hippocampus, amygdala, and the ventromedial PFC,” noted the authors. “Building on this finding, baseline REM measurements may serve as a non-invasive biomarker for resilience to trauma or, conversely, to the potential development of Post-Traumatic Stress Disorder following trauma.”
Sources: Lerner I, Lupkin SM, Sinha N, Tsai A, Gluck MA. Baseline levels of rapid-eye-movement sleep may protect against excessive activity in fear-related neural circuitry. J. Neurosci. doi: 10.1523/JNEUROSCI.0578-17.2017 (2017); https://www.eurekalert.org/pub_releases/2017-10/sfn-bsl101717.php