“The witching hour… was a special moment in the middle of the night when every child and every grown-up was in a deep, deep sleep, and all the dark things came out from hiding and had the world all to themselves.”
-Roald Dahl, The BFG
In folklore and literature, the sleeping hours represent a state of heightened vulnerability, a time when the “ghoulies and ghosties, and long-leggedy beasties” roam free and wreak havoc. Today, neuroscientists are unraveling the biological underpinnings of nightmares, night terrors, and other sleep disturbances.
Recently, I had the chance to sit down to discuss these nighttime phenomena with biologist H. Craig Heller, PhD, a member of the Stanford Neurosciences Institute and an expert in the neurobiology of sleep.
What are parasomnias and what causes them to occur?
Parasomnias include nightmares, night terrors, and sleepwalking — the really bizarre aspects of sleep.
Normal sleep phasing, timing, and coordination require smooth transitions between wake, non-REM sleep, and REM sleep. When the integration is imperfect, the pathologies of sleep may occur.
For example, sleep paralysis is caused by an inappropriate transition between REM sleep and wakefulness. During REM sleep the cortex is activated, so to keep the body asleep, inputs and outputs are blocked — your body becomes paralyzed. Sleep paralysis occurs when REM paralysis persists as you return to wakefulness. You are coming out of a paralyzed state in which you are freely associating, and this can lead to hallucinations that you’re being restrained.
The opposite can also happen: During REM sleep, motor inhibition can be lost, and you can act out your dreams — which can be violent.
In your mind, what's the scariest sleep disorder?
Sleepwalking. Sleepwalking occurs during NREM sleep, and in contrast to nightmares or violent movements that can occur during REM sleep, sleep walking is more an extension of normal waking behavior, but you are not aware of what you are doing. As a result, sleep walkers can get into dangerous situations.
In one case, a guy sleepwalked out of his house during winter in Minnesota, before eventually returning to his home and to bed. The next morning, he woke up, pulled back the covers, and found his feet seriously frostbitten. They were a mess. You would think he would be in tremendous pain, but he didn’t wake up.
Also, in cold places in the winter, kids can sleep walk out of the house and freeze to death. In one case a child was found dead in the morning just curled up in a snowdrift immediately outside his house. Some apparent suicides may even be cases of sleepwalking.
You mentioned that people can act out their dreams if the REM sleep paralysis is lifted or not activated – is this phenomenon the same as sleep walking?
No, it’s not the same. Loss of motor inhibition during REM usually results in dramatic, extreme movements, whereas sleep walkers are more likely to act in ways that are simple extensions of normal waking behavior. Sleep walkers may eat and maybe even drive a car and not remember it the next morning. Those with REM sleep disorders are acting out the bizarre context of nightmares.
One of my teaching assistants had a particularly dramatic experience: One night she was dreaming that she was being chased by a giant cockroach; she stood up on her bed and started to run, and she ran right off the bed and into the bureau and broke her back.
In some cases, people dream they are fighting an enemy, so they’ll punch or kick the person in bed with them. There are court cases involving murder and the defense is that the individuals were asleep. Court decisions have gone both ways. In one episode, a woman was dreaming she was being attacked, and when her father came into her room to wake her, she got a gun that was in the bedside drawer and shot him.
What's the difference between a nightmare and a night terror?
Nightmares occur during REM sleep and are simply dreams with a strong emotional component. Night terrors are not associated with a consciousness narrative like a dream. They are momentary almost-awakenings, accompanied by manifestations of intense anxiety. Someone, usually a child, will sit up and start screaming, and is usually inconsolable. If woken up, the child generally can’t tell you what it was.
Do people who watch horror movies or consume other “scary” media have more nightmares?
I don’t know if anyone has studied that, but definitely your dreams can be influenced by your daytime experiences. Psychologists used to think that you’re working out your internal Freudian problems during dreaming, but this theory has since been disregarded.
Currently, the prevailing opinion about dreams is that they’re an epiphenomenon. We don’t know why, but for some reason, the cortex has to be reactivated periodically during NREM sleep. That reactivation is REM sleep. If you happen to be in an emotional state (from watching a scary movie, or reading Q&As about sleep disorders, for example), you may be more inclined to have nightmares during those episodes of REM sleep.
Erica Seigneur is a neurosciences PhD student at Stanford.
Previously: Biodesign fellows take on night terrors in children, Violent behavior a concern while sleepwalking and Stanford study shows millions of Americans are prone to sleepwalking
Photo by Michael Koralewski