Every day, an enormous amount of data enters our brain, a conglomeration of cells that – like a computer – has limited storage space. Unlike a computer, however, brains don’t come with external hard drives or higher memory options. We get what nature gives us.
“Sorting, consolidating and saving what’s important from our daily influx of information is a continual and fascinating process, and it happens mostly during sleep,” said CU Anschutz neurologist Brice McConnell, MD, PhD. “Our brains switch into maintenance mode, and all this stuff happens without our awareness, kind of behind the scenes.”
McConnell, who leads research at the CU Anschutz Alzheimer's and Cognition Center that monitors sleep brain waves through electroencephalography (EEG) in search of early signs of disease (see sidebar at bottom), shared a behind-the-scenes look into how the body’s master orchestrator works when the curtain falls.
The brain digests a stream of information during awake hours, initially storing memories in detail, especially if they involve brand-new information and moments of life-altering importance (say, the birth of a child, wedding proposal or news of a society-changing invention, such as the internet or electric car).
“We call that episodic memory. You remember how you learned it, where you learned it, who you learned it from,” McConnell said.
But with only so much storage space, the brain has to decide which memory events are disposable and which should be kept, stripped of most details, and stored with similar information in its existing knowledge base. “And that's how we build concepts.”
When consolidating memories during sleep, the brain goes into a sort of instant-replay mode, shuffling information back and forth during rapid eye movement (REM) and non-rapid eye movement (NREM) sleep stages.
Hitting snooze: If you wake up feeling tired, you might have missed out on time in the deep sleep part of the non-REM sleep stage. During deep sleep, blood pressure falls, breathing slows and energy is restored.
“The same cells that were used when you were awake to process the information reactivate when you're asleep and play the whole thing back,” McConnell said. “During REM sleep, you’re doing the big-scale processing of information. You are figuring out how the information relates to everything else that you know about the world in a very global sense.”
During NREM sleep, short bursts of wake-like states occur, processing small units of information in very localized areas of the brain.
All of this information comes with an emotion attached, something that grabbed the brain’s attention in the first place, whether it was fear, anger, excitement, sadness, awe, McConnell said. And the brain then assesses how those emotions fit in memory consolidation.
“When you go through your sleep cycles, you're changing how you feel about the world based on the new information. Maybe we're very upset about something, and we sleep on it, and then the next day, we have this new perspective, and we say: I got a lot more upset about this than I should have," he said.
“And some of that is the passage of time, but a lot of that is that your brain actually changed how you feel about it through the processing of the emotional part.”
A bidirectional relationship exists between emotion and sleep, with poor sleep associated with some psychiatric conditions, such as depression and anxiety, and with day-to-day exaggerated emotional responses (think: short-tempered, irritable).
Sleep cycles: A typical night's sleep consists of four to five sleep cycles, with a complete sleep cycle lasting 90 to 110 minutes. The progression of each sleep cycle includes alternating non-REM parts followed by REM in this order: N1 (transitional), N2 (light), N3 (deep), N2 (light), REM.
“Sometimes, if we're experiencing things that are very emotional, it can mess up our sleep, and then if our sleep is disrupted, our emotions don't get a chance to reset.”
A bidirectional relationship between sleep and other diseases also exists, including neurodegenerative disorders such as Alzheimer's or Parkinson’s disease, McConnell said.
“If your brain is experiencing a neurologic disorder that disrupts sleep, your sleep isn't going to restore your brain, and then if your brain hasn't been restored from sleep, it's going to worsen the neurological problem,” McConnell said. “It’s a vicious cycle.”
Scientists believe the optimum period for brain-maintenance mode, while different for everyone, typically falls between six and eight hours a night, McConnell said.
“Think of it as a U shape, with the bottom of the U the six-to-eight-hour range. “If you're consistently not in that kind of sweet spot and going further and further out of bounds (up either the short sleep side or the long sleep side of the U), it’s probably a sign that something isn't optimal,” McConnell said, meaning you should see a doctor to explore the cause.
Use of sleep aids today, such as noise machines and CBD/THC edibles, suggest people aren’t getting the prescribed amount of restful slumber every night. But the research isn’t in on whether these popular crutches are safe for brain health with regular use, McConnell said.
“The frustrating answer is: We don't know,” he said. “It’s probable that long-term or loud exposure to white noise when you're sleeping could have some effect that you wouldn't want to have happen. But we really don't have enough data right now to say that it's definitely bad,” he said.
Sweet dreams: In REM sleep, most vivid dreams occur, muscles become temporarily paralyzed to prevent acting out, and heart rate and blood pressure increase to near awake levels.
“We do know, though, that disruptive noises are bad. So, if you can't sleep because your brain is waking up because of other noises (neighbors, traffic, roommates), then the white noise might be a trade-off for masking the noisy environment.”
Research on edibles with CBD and THC components is challenging to do, McConnell said. “One product can have all different kinds of cannabinoids in it,” he said.
“But anything that disrupts memory processing is going to disrupt the normal function of sleep.” Scientists do know that many sleep medications today change the brain wave patterns that coordinate memory processing, such as slow waves of sleep, McConnell said.
“And when you change the brain wave patterns, you start to mess up the system. You’ll change the balance between non-REM and REM sleep that supports memory functions,” he said. “So, the best thing to do if you're not sleeping is to try to recover the ability to sleep non-pharmacologically.”
Scientists tap the brain to detect health issues
Work by Brice McConnell, MD, PhD, and his research team analyzing changes in memory reactivation brain waves has already resulted in a nighttime “digital biomarker” that uses a wearable headband to detect early signs of Alzheimer’s disease in studies.
Now, with new funding behind a second study phase, his team has enlisted the help of artificial intelligence (AI) to improve this technology for detection of Alzheimer’s disease and a wider range of health issues.
Partnering with colleagues in biomedical informatics, biostatistics and mathematics, McConnell is leading a team of investigators in developing sophisticated AI algorithms to help decode brain waves in search of signs of heart disease and other metabolic disorders, top killers in the United States today.
The research is funded by the National Institutes of Health (NIH) and involves thousands of brain recordings archived in NIH repositories for the past 30 to 40 years. Scientists will seek connections between sleep and diabetes, heart disease and metabolic symptoms such as high blood pressure and cholesterol, among other things.
Alzheimer's remains a chief focus of his research, said McConnell, an assistant professor of neurology in the CU Anschutz School of Medicine. “But we've expanded the focus into brain health monitoring in general. And these things are all interrelated,” he said, noting that cardiovascular risk factors are also major risk factors for developing Alzheimer's disease.
“Using the brain, the master regulator of overall health, we can start to see if you are at risk of developing a certain kind of disease and then give you ideas of what to do about it.”