Picture the brain at night. It’s mostly quiet except during rapid eye movement (REM) sleep. Then clusters of neurons in the brain stem start firing away like mad. These bursts of activity are perfectly normal during REM sleep, alternating with periods of quiet non-REM sleep through most of the night.
The brains of people with insomnia are more active at night—even during non-REM sleep. This activity isn’t often noted in sleep studies, where the point is to identify dominant wave forms. But looking closer, scientists are discovering slight but crucial differences in insomniacs’ brain waves at night, which may explain our trouble falling and staying asleep.
Alpha wave intrusion is a term used to describe the wake-like brain activity observed during the deep sleep of people with fibromyalgia and major depression. Now a new study in the Journal of Sleep Research presents evidence of abnormal alpha wave activity in insomniacs’ brains at night. Here are the two main findings:
Trouble Falling Asleep
The descent from wakefulness into deep sleep occurs fairly quickly in healthy sleepers. The pressure to pay off the day’s sleep debt is strong, compelling a rapid descent into deep (slow-wave) sleep.
But in people with sleep onset insomnia, who typically take more than 30 minutes to fall asleep at night, the descent takes quite a bit longer, research shows. Insomniacs—for unknown reasons—seem to have reduced sleep pressure. Not only does it take us longer to fall asleep. It also takes us longer to descend into deep sleep, the really restorative stuff.
Why the Slow Descent?
The research team investigating alpha wave activity looked at the sleep studies of 18 good sleepers and 10 insomniacs and found one difference that occurred before sleep began. Alpha waves—associated with a relaxed, meditative state of consciousness that occurs when the eyes are closed—are predominant in the period leading up to sleep. They’re generated by neurons firing at frequencies of 7.5 to 12.5 cycles per second.
As the healthy sleepers in the study were falling asleep, the alpha rhythms in their brains began to fluctuate and decay. But the alpha wave activity in insomniacs’ brains continued going strong.
Sleep onset insomnia may have something to do with decreased alpha variability, the researchers concluded. Insomniacs are relaxed and ready for sleep—yet (again for unknown reasons) we remain stuck in alpha mode.
Waking Up at Night
Alpha waves may also play a role in sleep maintenance insomnia. Polysomnogram studies show that normal sleepers awaken at least a few times a night but are mostly unaware of these awakenings.
People with sleep maintenance insomnia, in contrast, are conscious of waking up at night. These awakenings make our sleep feel fitful and less restorative. (And some sleep maintenance insomniacs are told their problem involves alpha wave intrusion following a sleep study.)
Adults spend up to 80% of the night in non-REM sleep, and in the alpha wave study, different kinds of alpha activity occurred in the brains of healthy sleepers and insomniacs throughout non-REM sleep. Brief arousals in the healthy sleepers were characterized by alpha waves that stayed well below the frequency of alpha waves during conscious wakefulness.
But the alpha frequencies in participants with insomnia rebounded to wake levels. In this situation, a sleeper might be easily awakened by noise or movement and memories could be formed. It might account for why so many insomniacs complain of light and/or broken sleep.
Higher alpha frequencies during brief arousals and lower alpha variability at the approach of sleep fit with the hyperarousal theory of insomnia, which suggests that people prone to insomnia experience higher levels of arousal around the clock. As for how to correct these alpha abnormalities, we’ll have to wait and see.