A study reveals how getting less sleep than normal may impair the brain’s capacity to regulate fear. The finding helps explain why frequent sleep disturbances make people more prone to anxiety and post-traumatic stress disorder (PTSD).

Sleep plays a crucial role in maintaining mental health. For example, people with insomnia are approximately three times as likely to develop an anxiety disorder compared with those who sleep normally, according to a systematic review of research published in 2019.

Other studies find that people who experience frequent sleep disturbances — a common issue for health workers and military personnel — have a higher risk of PTSD.

Not getting enough rapid eye movement (REM) sleep, which is the sleep stage when most dreaming occurs, seems to be a particularly important factor in this increased risk.

Sleep in general, and REM sleep in particular, are known to play a vital role in “fear extinction.” This is the process of learning where the stimuli previously associated with unpleasant sensations or experiences now become harmless.

The importance of REM sleep

The researchers speculate that sleeping only the first half of the night deprives a person of most of their REM sleep, which occurs predominantly toward the end of a normal sleep period.

Studies have found that REM sleep helps people unlearn fearful memories from the previous day. The new research suggests it is also important for unlearning fear conditioning on the following day.

The researchers were surprised to discover that fear-related regions in the brains of participants who they completely deprived of sleep did not activate during the experiment’s fear conditioning and extinction phases.

In the evening, when the researchers tested participants’ memories of the fear extinction, the pattern of activity in their brains was similar to that in the brains of subjects who slept normally.

The scientists speculate that a compensatory mechanism may kick in when people are totally sleep-deprived, protecting their brains from fear conditioning.

They write that a similar mechanism may explain why some people with depression experience a temporary easing of their symptoms through sleep deprivation therapy.

However, the current study suggests that partial sleep deprivation fails to activate this protective mechanism.

“Medical workers and soldiers often have curtailed or interrupted sleep rather than missing an entire night’s sleep […] Our findings suggest that such partially sleep-deprived individuals might be especially vulnerable to fear-related conditions such as PTSD.”

– Dr. Pace-Schott

The findings may also have implications for exposure therapy for PTSD and phobias, which involves exposing patients to fear-provoking stimuli in a controlled therapeutic setting. They suggest the treatment may not work well after a poor night’s sleep.

Medical reference: Medical News Today