Situations like being bullied at school, getting fired from a job or losing your train of thought during an important speech can feel mortifying when they occur. But in time, and with the help of sleep, the shame and embarrassment fade away. You can recall the experience without re-experiencing the emotional charge. This may not be the case for people with insomnia, results of a new study in the journal Brain suggest. Insomnia may involve disruption of the brain’s processing of emotional experience, burdening poor sleepers with emotionally charged memories. Here’s more about it.
Situations like being bullied at school, getting fired from a job or losing your train of thought during an important speech can feel mortifying when they occur. But in time, and with the help of sleep, the shame and embarrassment fade away. You can recall the experience without re-experiencing the emotional charge.
This may not be the case for people with insomnia, results of a new study in the journal Brain suggest. Insomnia may involve disruption of the brain’s processing of emotional experience, burdening poor sleepers with emotionally charged memories. Here’s more about it.
Biological Aspects of Insomnia
Insomnia used to be blamed mainly on bad habits and faulty thinking, but increasing attention is being paid to biological factors that underlie insomnia. Results of gene studies point to genetic factors that make people vulnerable to insomnia. Many insomnia risk genes are located in the limbic area of the brain, where the processing of emotion occurs. The possibility that insomnia has to do with disturbed emotion processing is what researchers in The Netherlands set out to investigate.
Past research has established a few things:
- When people experience a novel emotional event, such being shown graphic photos of war victims, functional MRIs (similar to movies showing activity in the brain) show strong evidence of activity in the limbic system. However, recall of those photos at a later time does not involve limbic activity.
- People with insomnia do not experience the same overnight resolution of emotional distress as normal sleepers do. In fact, studies conducted by Rick Wassing and colleagues showed that in insomniacs, emotional distress resulting from an unpleasant situation could linger for over a week.
A Working Hypothesis
People with insomnia are prone to fragmented sleep (particularly, fragmented REM sleep). It could be that in insomnia, an area or areas of the brain that typically go offline during sleep are not fully deactivated, resulting in continuing secretion of neurochemicals associated with alertness. One consequence could be the storage of long-term emotional memories that still retain ties to the limbic system and hence their emotional charge.
The research team decided to investigate the responses of normal sleepers and insomnia sufferers to novel emotional experiences and memories of past emotional experiences and then compare them. Their hypothesis was that in people with insomnia, brain activity during recall of distant emotional events would look more like brain activity during novel emotional events than in normal sleepers.
Preparing for the Study
Fifty-seven people participated, aged 18 to 70 years. Twenty-seven participants had a diagnosis of insomnia disorder and 30 were classified as normal sleepers.
At an intake interview participants shared information about shameful experiences they could recall from their past. Each participant also underwent a structural MRI brain scan and made a karaoke-style audio recording in which he/she sang along to a familiar tune.
A week later testing began. Throughout the testing, each participant was wired with electrodes to assess galvanic skin response (changes in sweat gland activity that would reflect the intensity of the participant’s emotional state) and was undergoing functional MRI that would capture and record activity in the brain.
An Ingenious Test of Emotional Intensity
There were two tests, the first involving measurement of participants’ reactions to a novel shameful experience. Participants in both groups, the insomnia sufferers and the normal sleepers, were told they would be exposed to recordings of their own singing and the singing of others, and that two researchers would be listening in. Then each participant had to listen to 16-second fragments of their own solo singing, unaccompanied by music. The fragments were intermixed with neutral stimuli consisting of fragments of the same song sung by a semi-professional singer. How’s that for a novel shaming experience!
The second test involved recall of five shameful events from the distant past. For 16 seconds participants were asked to remember each shameful experience. In between each shameful experience, participants were asked to recall a trivial non-emotional experience from the past. After recounting each memory, participants rated its emotional intensity.
What the Research Team Discovered
Analyzing the data, researchers found, predictably, that emotional stimuli were on average rated as more intense than neutral stimuli. In addition, data from subjective participant reports and assessment of galvanic skin response showed the following:
- The response to novel neutral and novel emotional experiences was similar in people with insomnia disorder and normal sleepers
- Normal sleepers’ response to remembered shameful events was similar to their response to remembered neutral events (i.e., the emotional charge that accompanied the original experience was gone).
- People with insomnia, however, had a stronger response to relived shameful memories than to neutral memories (suggesting continuing involvement of the limbic system).
Movies of the Brain Are Confirmatory
From the functional MRIs, investigators found the following:
- The shame participants felt as they listened to their own singing triggered intense limbic activity in the brains of both normal sleepers and people with insomnia
- Although memories of past shameful experiences did not induce a limbic response in normal sleepers, in insomnia sufferers, they did. In fact, in the brains of people with insomnia, limbic activity was noted in many of the same areas active during novel emotional experiences, notably, the anterior cingulate cortex.
“The findings,” write the authors, “suggest that normal sleepers activate a markedly different brain circuit while reliving emotional memories from the distant past as compared to when they are exposed to novel emotional experiences. In patients with insomnia, however, the brain circuits recruited with reliving distant emotional memories overlapped with the circuits recruited during a novel emotional experience.”
The restless REM sleep that often characterizes insomnia may be attributable to a failure to deactivate a part of the brain that, if shut down, could enable more restorative sleep and quicker recovery from emotionally painful experiences. There are ways to treat insomnia behaviorally, and some work pretty well. But only when more research into the causes of insomnia is conducted will researchers be able to find a cure.