A "Dreaming Signature" In the Sleeping Brain

Where do dreams originate in the brain? 

Dreams are probably one of the most mysterious neurobiological phenomenon that scientists can study. While the field generally agrees that they seem to be doing something--for example, helping the sleeping brain process the previous day's memories--they're really mostly still an enigma.

Case in point: until recently, scientists haven't really figured out when dreaming actually happens while we sleep. Every night we go through several sleep cycles, comprised of rapid eye movement (REM) sleep and deep, non-REM sleep. True to its name, people often roll their eyes during REM, and scientists used to think that's the only time dreaming can occur.

Part of this is based on brain activity measured during dreaming. When we go to sleep, the types and strengths of our brain waves change, overall dampening activity. However, during REM the brain generates high frequency waves that look like the kind during wakefulness. So of course scientists reasoned: similar brain waves equals similar alertness level, so dreaming must occur when the sleeping brain looks like it's awake, right?

In fact, REM and dreaming are almost synonymous: you rarely hear about the fringe cases of not dreaming in REM sleep, or dreaming during non-REM sleep.

But the problem is, those cases do exist. And they pose a conundrum: how can a brain in non-REM sleep, exhibiting brain waves opposite of what you would expect to see in wakefulness, be able to generate dreams?

This is the question that a new study in Nature Neuroscience tackled. Using EEG, the researchers carefully monitored the volunteer's brain activity while they slept, and randomly woke them during the night to ask whether they'd been dreaming. 

From the data, they found that while overall the dreaming brain generated slow wave activity, the hindbrain leapt into action during dreams, regardless of whether they occurred during REM or non-REM sleep. It's like a "dreaming signature" of the brain. 

And the signature was so accurate at predicting dreams that the researchers developed an algorithm based on brain activity patterns. When tested on a new group of sleep volunteers, the algorithm was roughly 90% accurate at predicting whether or not they were dreaming.

What's more, the researchers also found that the dreaming brain acted a hell lot like the awake one. For example, if you're dreaming of faces, the brain region that process facial recognition comes online; if the dream is about running, then the movement centers activate. This isn't super surprising, since we previously know that watching people do something or imaging doing something activates similar brain regions as if you were doing it yourself.

Finally, the team also found a specific brain signature for those times when you know you've been dreaming, but can't remember what the dream was about. (I've heard that keeping dream diaries can help train a person to gradually remember more, which makes me wonder what's changing in the brain.)

The authors claim that the study may give more insight into the nature on consciousness, since dreaming is basically periodically regaining consciousness in a background of unconsciousness. That's a really bold claim, and one I'm not particularly on board with.  

Overall though, really cool study. Also makes one wonder what's going on in the sleeping heads of lucid dreamers, who not only recognize that they're dreaming, but can also force the dream to go they way they want. 

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