New research has found that better-quality sleep is connected with reduced activity in brain regions implicated in fear learning. Thus, time spent in rapid eye movement sleep could be a good indicator of susceptibility to post-traumatic stress disorder.
Other conditions, such as epilepsy, have also been associated with sleeplessness, and a recent study covered by Medical News Today even suggests that there may be a causal relationship between sleep disturbances and ADHD.
Dr. Itamar Lerner, Shira Lupkin, and other researchers from Rutgers University in Newark, NJ, have now conducted a study indicating that better-quality sleep is linked with dampened brain activity in regions tied to fear learning.
The process of fear learning is the mechanism through which we attempt to predict exposure to threatening situations so that we react appropriately to preserve our safety.
Dr. Lerner and team conducted their study on a cohort of young adults, and their findings were published yesterday in the Journal of Neuroscience.
REM sleep impacts fear-related brain activity
Previous studies have aimed to understand the relationship between established fear memories — which have already taken root in the mind — and sleep in the context of PTSD.
The current study's goal, by contrast, was to establish whether or not a person's sleep patterns before witnessing a traumatic event might be a good predictor of whether fear memories will become established in the first place.
This, in turn, might indicate whether or not sleep patterns of brain activity associated with fear learning might be associated with an individual's susceptibility to PTSD.
In their study, Dr. Lerner and his colleagues asked the participants — who were 17 healthy Rutgers University students, of which five were female — to monitor their own brain activity during sleep for approximately 1 week.
For this purpose, they used unobtrusive devices such as a headband that allowed them to measure their brainwaves and a bracelet recording arm movements. The participants also used a sleep log to record their sleep habits and patterns.
In addition to the self-monitoring, the participants were involved in a neuroimaging experiment that conditioned them to associate a neutral image — of a colored lamp — with the induction of a mild electric shock.
The researchers found that those who spent more time in the rapid eye movement (REM) phase of sleep — which is associated with dreaming — also had dampened activity in, as well as reduced connectivity between, the amygdala, the hippocampus, and the ventromedial prefrontal cortex during fear learning.
These three brain regions are variously implicated in our response to stress factors, as well as in memory and learning.
For instance, the amygdala and the hippocampus are known to work together in the context of the "fight-or-flight" response — that is, how we react to a perceived source of threat — as well as in the process of memory formation.
REM may lower norepinephrine levels
To consolidate their findings, the team wanted to, and did, replicate their initial results in another study using polysomnographic sleep monitoring — recording brainwaves, heart rate, and eye movement — just before the fear conditioning experiment.
Following their tests, the researchers believe that more time spent in the REM sleep phase has the role of moderating levels of the neurotransmitter norepinephrine, which is also known as "noradrenaline," in the brain.
Norepinephrine is linked to the regulation of the fight-or-flight response, so they believe that lower levels of norepinephrine could explain the reduced susceptibility to stressful stimuli that would normally induce fear.
"Ultimately," they conclude, "our results may suggest that baseline REM sleep could serve as a non-invasive biomarker for resilience, or susceptibility, to trauma."