From scientificamerican.com
You say you haven’t slept all night. Brain scans say you have. New science says both inferences may be right
Desperate for sleep, you go to a sleep clinic, where your head is fitted with electrodes to record your brain waves through various sleep stages. In the morning, you report that you barely slept at all. Yet according to the test—polysomnography, the gold standard for sleep measurement—you slept all night.
You’re not the classic example of a person with insomnia who waits for sleep to come, maybe checks the clock, paces, reads and waits for morning. What you have has been called subjective insomnia, paradoxical insomnia or sleep misperception. Scientists have doggedly attacked this stubborn puzzle for decades without result—until now. Now they say that you have not been misrepresenting your sleep; they have been mis-measuring it.
The most recent studies, using far more enhanced measurement, have found that many people with subjective insomnia show different brain activity from good sleepers—throughout the night. Neuroscientist Aurélie Stephan and colleagues at the Netherlands Institute for Neuroscience (NIN) realized that something unusual was going on after they asked people in their study to put onto their head a net of 256 electrodes rather than the typical six to 20 used in sleep clinics. In one series of experiments, the researchers woke sleepers about 26 times on average during the night. The participants were asked whether they’d been asleep or awake and what they’d been thinking about.
The most remarkable finding, Stephan says, is that these people showed pockets of arousal in the form of fast brain waves during rapid eye movement (REM) sleep. REM is the stage in normal sleep when your brain should completely disconnect from the systems that keep you aware and vigilant, Stephan says.
People with subjective insomnia with this interrupted REM do not experience their sleep as restful. When wakened, they reported having had thoughts similar to those when awake—adding lettuce to their shopping list, say, or reminding themselves to call their cousin. They were less likely to have what University of Montreal neuroscientist Claudia Picard-Deland calls immersive dreams, in which you feel physically present in the dream world and are fleeing down a dark hallway, feeling the hardness of the floor or battling a dragon, sensing its hot breath.
In a study of normal sleepers Picard-Deland recently presented at the the Cognitive Neuroscience Society’s annual meeting, participants said they felt most deeply asleep during immersive dreams, which occurred in the REM stage. People with interrupted REM, as Stephan’s research shows, do not report immersive dreams. They do not feel they’ve slept deeply, and they report fatigue similar to that of people who actually sleep very little.
Perhaps even more important, says NIN sleep scientist Eus van Someren, interrupted REM is strongly linked to disorders such as post-traumatic stress disorder (PTSD) and anxiety. If two people experience the same level of trauma, a good sleeper is probably less likely to develop PTSD than someone with disturbed sleep, he says. Those with disturbed sleep are therefore more vulnerable to developing PTSD. It’s a vicious cycle.
This occurs because interrupted REM interferes with the overnight dissolving of emotional distress that has accumulated throughout the daytime, which typically happens during good sleep. “Sound REM sleep is the only state during which the brain has a ‘time-out’ of noradrenaline [norepinephrine],” van Someren says. “The neurons are not firing anymore, so they don’t release noradrenaline downstream in the brain. But if you have even the slightest arousal from REM sleep..., then noradrenaline shoots up very fast.” He believes those with interrupted REM experience this arousal repeatedly and never reach the typical quiescent state that allows for the processing of troubled emotions.
A study headed by van Someren’s former graduate student Rick Wassing, now at Macquarie University in Australia, demonstrates this experimentally. The researchers exposed people to a distressing emotional experience for three days in a row: they had to listen to a recording of themselves singing—often out of tune—to karaoke, which aroused shame. As measured by their physiological responses, normal sleepers felt less distress after a night’s sleep. Those with disturbed sleep felt more.
The percentage of people with insomnia that have interrupted REM is unknown, but these insights are suggesting new personalized treatments for insomnia, which is now understood as existing on a spectrum. Such treatments may be especially beneficial to people with insomnia who also have depression and anxiety disorders.
Currently, cognitive behavioural therapy for insomnia (CBTi) is the standard intervention for insomnia. People with insomnia learn to decrease their anxiety about sleeping and to employ behavioural strategies aimed at better sleep. But CBTi does not work for everyone. Those with interrupted REM, in particular, probably need different solutions.
One behavioural strategy used in CBTi—sleep restriction—does show promise for people with interrupted REM, however. Some sleep-restriction methods involve shortening a person’s time in bed to the average amount that they actually sleep per night. Other methods delay a person’s bedtime.” For example, If a person objectively sleeps for 5.5 hours, the experts allow the person to be in bed only for six hours. A preliminary lab study in which participants delayed their regular bedtime by two hours showed that such sleep restriction can reduce the number of arousals during REM. The researchers are hoping to replicate these results in a larger study of people sleeping at home.
This new science also opens the way for drug interventions. The NIN group is seeking approvals to test whether a beta-blocker typically prescribed to lower blood pressure might mitigate the effects of continuous bursts of norepinephrine. The researchers are also considering testing the blood pressure drug clonidine in the hopes that it may help the brain reach a more quiescent state.
Until these interventions are available, says sleep researcher Geoffroy Solelhac of the Centre for Investigation and Research in Sleep in Switzerland, “just understanding that their sleep is objectively different is reassuring to patients. They feel a sort of relief.” Knowing all that may even help them sleep better.
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