[ ♪INTRO ].

In the award-winning movie Sleepwalk with Me, based on the one-man show of the same name, comedian Mike Birbiglia describes the hilarious and often startling things his body does when he's sleeping. Birbiglia has REM sleep behavior disorder, or RBD, a sleep disorder that causes people to physically act out their dreams.

And while that might sound goofy at first, think about the last dream you had, where you were running from homework monsters or throwing punches at Voldemort. Maybe… maybe you wouldn't want to act those out in real life. Thankfully, RBD can be treated.

But in some cases, it can also tell a deeper story about what's happening in someone's brain. RBD affects roughly 1% of the population — although that number is slightly higher in older people. And it's often associated with a huge range of things.

We're talking everything from pre-existing, neurodegenerative diseases like Parkinson's to narcolepsy to tumors to certain antidepressants. But ultimately, it happens because something interferes with the brain during sleep. Typically, about 90 minutes after you fall asleep, you begin the REM sleep stage.

REM stands for “rapid eye movement,” because it's when your eyes move back and forth under your closed eyelids. But it's also the stage where you experience most of your dreams. During this time, your brain activity rises to near-waking levels, and your breathing and heart rate speed up.

But typically, your body isn't able to move. That's because, during REM, structures in the brainstem prevent the body from acting out dreams by relaxing muscles and suppressing motor activity. Specifically, clusters of neurons from a structure called the pons activate neurons in another structure called the medulla.

Then, the medulla sends signals to motor neurons in the spinal column to keep the muscles relaxed and put motor activity on pause. In RBD, that's where the trouble lies. An issue in the pons results in a failure to turn off those motor neurons, so someone can move as much as they want during a dream.

Now, to be clear, a little movement during sleep is totally normal. What these brainstem areas do is stop big movements like kicking and arm-swinging. Without this kind of inhibition, a person might just knock a lamp off their nightstand or bruise themselves by kicking their footboard.

But for those who share a bed, this disorder can have more serious consequences. Like, in 1986 when RBD was formally identified, researchers described men who would dream they were defending their wives from an attacker, only to wake up and find they were actually attacking their wives. Which, understandably, would be pretty alarming.

It's kind of thing that you do want to treat. And the very good news is, RBD is treatable, and there are two medications research has shown to be effective. The first choice for many doctors is clonazepam, a medication traditionally prescribed for seizures.

It does come with a number of side effects, including drowsiness, dizziness, and incontinence. But for some, that's better than the alternative. The other medication is melatonin, the same hormone our brains secrete to make us sleepy at night.

It has minimal side effects, but it only seems to work for some patients. Unfortunately, it's not clear right now why these medications work. But, they do seem to.

This being said, even though RBD is treatable, it's still something doctors tend to keep a close eye on. Because sometimes, this condition can signal that something bigger is changing in the brain. Earlier in this episode, I mentioned that RBD is often associated with pre-existing neurodegenerative diseases, like Parkinson's.

And that's true. But researchers have also noticed another connection here. They've found that many otherwise-healthy people with RBD actually go on to develop neurodegenerative diseases later in life.

For example, a 2009 study followed 93 patients who had been diagnosed with RBD at a hospital's sleep lab. People who had no other signs of neurodegenerative disease. Researchers followed the health of these patients for several years, and monitored who got diagnosed with what and when.

Then, based on those results, they estimated the risk of developing a neurodegenerative disease within 12 years after an RBD diagnosis. And that risk was a whopping 52% — basically, a one in two chance. And other studies have found similar results.

Additionally, papers have identified RBD in an average of 24% of existing Parkinson's cases, 88% of cases of multiple systems atrophy, and 76% of Lewy body dementia cases. As for why? Well, these conditions are all types of alpha-synucleinopathies.

Those are diseases caused by buildup of the protein alpha-synuclein in — where else? — the brainstem. The same region of the brain that causes RBD symptoms. Researchers aren't sure exactly how all of this is connected, and it's something they're still looking into.

But there does seem to be a link here between alpha-synuclein in the brainstem and RBD. Hopefully, as we figure it out, we'll learn more about how these diseases develop and progress. For now, though, RBD can at least be the canary in the coal mine, letting people know something could be up a decade or more before they show symptoms of full neurodegenerative disease.

Again, not everyone with RBD will go on to develop these conditions. But for those who do, treatments for these diseases are more effective when they're administered early. And that counts for a lot.

REM sleep behavior disorder is a reminder that our brains are big, connected systems. So, the more we learn about specific conditions, the better-equipped we are to understand all kinds of other things. After all, research into this rare sleep disorder could have a lot to teach us about some of the most common brain diseases.

Thanks for watching this episode of SciShow Psych. If the symptoms we just described are ringing a bell for you, consider reaching out to your doctor. Because we can tell you a lot about what RBD is, but we're definitely not medical professionals and this is not a diagnostic tool. [ ♪OUTRO ].