Insomniacs are haunted by painful recollections and trivial missteps because their brains aren't processing emotional distress as they sleep, new research suggests.
Their nighttime awakenings could be interrupting this crucial neurological task, putting them at increased risk of depression and anxiety, Dutch scientists say.
An estimated five to 10 per cent of adults worldwide have insomnia disorders. Australian surveys have shown between 13 and 33 per cent of the adult population have difficulty getting to sleep or staying asleep.
A recent federal government inquiry called for sleep to be made a national priority and recognised as a "third" pillar of a healthy lifestyle alongside diet and exercise.
Two Dutch studies investigated the way sleep affects our ability to process negative emotions by monitoring brain activity as participants recall upsetting past memories, and participating in the universally embarrassing activity: karaoke.
In the first study, 64 people listened to playbacks of their own karaoke performances as they butchered the warbling high-notes of Gloria in Excelsis Deo or the Dutch national anthem.
They listened to the recordings before and after a night's sleep, explained post-doctoral fellow Rick Wassing, who led the research at the Netherlands Institute of Neuroscience.
They found the distressful, self-conscious emotions of shame had eased in good sleepers overnight.
"Their physical reactions to the recording adapted, and also emotionally they didn't feel so bad," Mr Wassing said.
Strikingly, insomniacs felt worse about their recordings the next day, found the study published in Sleep.
"It seems that the poor night's sleep actually aggravates their physically perceived distress," Mr Wassing said.
In the second study, the researchers used functional magnetic resonance imaging (fMRI) to map the neurobiological differences between the brains of good sleepers and insomniacs.
Another 57 people listened to their karaoke recordings and were also asked to relive painful past memories for at least 60 seconds.
The fMRI showed all participants processed their newer emotional experiences (the karaoke recordings) in the same way, with the activation of their limbic systems - the part of the brain that deals with emotions and memories.
But when it came to the much older, distressing memories, it was only among the insomniacs that the limbic circuitry lit up, specifically the anterior cingulate cortex (ACC), which connects the "emotional" limbic system with the "cognitive" prefrontal cortex.
They also had a physical emotional reaction, monitored by electrodes attached to their hands.
"Good sleepers, on the other hand, no longer activated this area of their brain, nor did they show physical emotional reactivity," Mr Wassing said.
Just as the sleeping brain works to strengthen some neural connections - selecting the important experiences or knowledge that is important to remember - it also disconnects or mitigates connections that cause emotional distress.
"Insomniacs continue to be haunted by past memories in a way people who sleep well are not," said Mr Wassing who plans to continue his work at the Woolcock Institute of Medical Research in Sydney.
For more than 15 years, insomnia has disrupted Rose Stacey's life, affecting her studies, work and relationships.
During her worst weeks, Ms Stacey might get four to five hours of broken sleep a night, leaving her physically drained and emotionally exhausted.
"It's hard to describe just how terrible you feel," the senior public relations manager said.
"I can very quickly become emotional, which can be very difficult in professional settings."
In the midst of bad periods of insomnia, she ruminates over minor missteps and bad memories.
"It can be something that happened quite some time ago and I'll replay it over and over in my mind," Ms Stacey said.
"It's a never-ending cycle because I'll be thinking about these things as I'm struggling to fall asleep."
The findings could help explain why rates of depression and anxiety are higher among people with insomnia and the importance of getting diagnosed and treated early.
"Symptoms overlap considerably with the symptoms of depression and anxiety," Mr Wassing said, including "mind chatter" known as rumination, worrying, stress, and the increased activation of the central nervous systems.
Mr Wassing plans to investigate how CBT may help insomniacs get a better night's sleep and restore their ability to process emotional stress.
- SMH/The Age
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