Why does insomnia make it hard to move past distressing experiences?
This was one of the findings of a new study from the Netherlands Institute for Neuroscience in Amsterdam.
The study also revealed how brain differences between people with and without insomnia might explain it.
The participants underwent the scans as they relived embarrassing experiences from decades ago plus a recent memory from just a week ago.
The scans showed that, when the group without insomnia relived old embarrassing memories, the brain circuits they activated were "markedly different" to those they activated as they recalled more recent embarrassing memories.
However, when those with insomnia recalled old embarrassing memories, the brain circuits they activated overlapped with the circuits that were active when they relived new embarrassing memories.
The overlaps occurred particularly in the anterior cingulate cortex (ACC), which connects parts of the brain involved with emotional and cognitive processing.
First study author Rick Wassing says that in people with insomnia, sleep does not help alleviate emotional distress. "In fact," he adds, "their restless nights can even make them feel worse."
Insomnia and 'karaoke-style' study
According to figures from the American Sleep Association, about 30% of adults in the United States report experiencing "short-term issues" relating to insomnia, while 10% report persistent insomnia.
Experiencing difficulty falling asleep is not the only or the main symptom of insomnia.
Other symptoms — such as moodiness, a lack of energy in the daytime, irritability, and struggling to focus on work — may also occur.
The authors note in their study paper that although the term insomnia suggests that the issues relate only to sleep, a diagnosis requires other measures, too — including many that relate to "daytime complaints" and "round-the-clock disturbances."
The results concerning the recent embarrassing event formed part of an earlier study, in which the team had examined emotional distress in people with and without insomnia as they recalled performing a "karaoke-style" solo song.
The scientists had invited the participants to sing, without musical accompaniment, while wearing headphones that prevented them from hearing themselves. This made it difficult for them to find the right pitch.
About a week later, just before undergoing MRI scans, the participants — as well as some of the researchers — listened to the solo singing recordings.
On the first playback, all of the participants reported having feelings of shame and embarrassment. However, after a night of sleep, those who slept well reported feeling much less distressed.
Those with insomnia did not: Their emotional distress was even more marked after a restless night.
Emotional circuits fail to disengage
The new findings suggest that the ACC, which helps regulate emotion, also has an important role in insomnia.
Previously, when looking for causes of insomnia, scientists had tended to focus on the parts of the brain that control sleep.
The study authors posit that people with insomnia have genes in their ACC that do not activate correctly during rapid eye movement sleep. This stops the brain from disengaging emotional circuits from the memories of distant distressing events.
"Brain research now shows that only good sleepers profit from sleep when it comes to shedding emotional tension."