In 2021, a group of researchers at the Paris Brain Institute, including Andrillon, discovered that these self-experimenters had gotten it right. Waking up from this earliest sleep stage, known as N1, seemed to put people in a “creative sweet spot.” People who woke up after spending around 15 seconds in the hypnagogic state were nearly three times more likely to discover a hidden rule in a mathematical problem. A couple years later, another study led by Horowitz at MIT found that it’s possible to further boost creativity in people emerging from this state by guiding what they dream about.
It’s not exactly clear why hypnagogia appears to boost creativity. One possibility is that the process of falling asleep “requires us to release control over our thoughts,” said Karen Konkoly, who studied lucid dreaming as a postdoctoral fellow at Northwestern University and now consults for the sleep start-up Dust Systems (co-founded by Horowitz). “As our executive control over our mind relaxes, we can perhaps access a broader semantic network of information, which could help creativity.” Andrillon agrees that the sleep transition produces a state of “free-wheeling consciousness” that unshackles the brain from its regular ways of thinking.
Like houses slowly shutting off their lights as a town falls into slumber, the brain gradually turns to night mode. Sleep starts at the center of town: Neurons deep in the brain, such as those in the ancient control center known as the hypothalamus, fire signals to suppress arousal circuits. Nearby brain regions such as the thalamus, which relays information from your senses to the rest of your brain, shut off first. Minutes later, the cortex, which is involved in more conscious, high-order thinking, follows suit. It shuts down from the front of the brain, where planning and decision-making occurs, to the back, where senses such as vision are analyzed.
During this transition, as some parts of the brain shut down while other parts remain awake, we can sometimes experience dreamlike thoughts. In this hypnagogic state, many people are “one foot in dreams and one foot in the world,” Horowitz said. Some people hear things; others have visions. These are like dreams but lighter: projections against the scaffold of the real world, which is still in our grasp.
“We could think that there’s a function” to these mental experiences, said Sidarta Ribeiro, a neuroscientist at the Federal University of Rio Grande do Norte in Brazil. “But maybe there isn’t. Maybe it’s a by-product of what’s going on in the brain.”
Sidarta Ribeiro and his team showed how daytime experiences can show up in hypnagogic imagery early in the process of drifting to sleep.
With your eyes shut and your senses powering down, you’re no longer getting much input from the outside world. But you’re still getting signals from inside the brain, maybe remnants of the day’s experiences. Ribeiro and his team recently reported that a person’s daytime experience can show up in hypnagogic imagery early in the process of drifting to sleep, adding to other studies that made similar findings.
Some researchers are using this state between sleep and wakefulness to study the nature of consciousness itself. “If you can track what’s going on in the brain when you go from those two opposite worlds, that would give you a lot of insights as to how consciousness fluctuates,” said Nicolas Decat, a graduate student studying sleep and consciousness at the Paris Brain Institute. In preliminary research that’s not yet peer-reviewed, Decat used an EEG to record the brain waves of more than 100 people as they were falling asleep. Following the techniques of Dalí and Edison, he had participants hold bottles so that as they drifted off, the bottles would fall and make a sound to wake them up.
By comparing the participants’ brain waves with their self-reports about what crossed their minds, Decat realized that some dreamlike imagery had occurred while they were technically awake, and some voluntary thinking had occurred while they were technically sleeping. For example, one participant reported ants crawling on her back even as the EEG documented the fast and frequent brain waves of wakefulness. Another reported having conscious thoughts about how they were falling asleep while they were technically asleep, based on slow and infrequent brain waves.
The unpublished data suggests that sleep states may not be the best way to categorize sleep consciousness. “Being awake or asleep does not fully determine what crosses your mind,” Decat said. The data “challenges the popular view that when you’re awake, you have certain thoughts. When you’re asleep, you have dreamlike imagery. It’s not necessarily like that.”
The transition to sleep can last for tens of minutes. That means it’s fairly easy for researchers to study — far easier than the process of waking up, which happens much more quickly and in a less controlled way. It’s much harder to predict when someone’s going to wake up.
Good Morning, Sunshine
Aurélie Stephan, a postdoctoral researcher at the University of Lausanne in Switzerland, grew interested in the wake-up process when she was studying a phenomenon known as paradoxical insomnia. Unlike people with insomnia, who are up all night without sleeping, people with paradoxical insomnia believe that they’re up all night even though their brain waves show that they’re asleep. “They sleep as much as good sleepers … so it’s a mystery,” Stephan said.
To understand this problem, she needed to first study a more typical wake-up process. When a good sleeper wakes up, what is their brain doing?
In a recent study, she examined more than 1,000 different awakenings or arousals — transitions from being asleep to being awake — on a timescale of seconds. She observed a curious slow brain wave in the data from good sleepers as they woke from non-REM sleep. Based on past animal studies, Stephan and her team hypothesized that this slow wave emanated from a spot deep in the brain.
The sleep researcher Laura Lewis believes that sleep disorders such as insomnia are “defined by problems with the state switching” between sleep and waking life.
After this signal, she saw the cortex wake up (as brain waves grew faster) from the front, which manages executive function, to the back, where vision and other senses are processed. When people woke from REM sleep, their cortex woke up in the same way, but without the preceding slow wave.
The presence of this unique slow wave was correlated with how people felt when they awoke, Stephan found. Participants who showed the signal woke up less drowsy than those without it. This suggested, but didn’t prove, that this might be an arousal signal that assists the wake-up process, Stephan said.
“They have done a very good job of finding this signature of the sleep-to-wake transitions,” said Luis de Lecea, a molecular biologist who studies sleep transitions in animals at Stanford University and was not involved with the study. They created a “detailed portrait,” Lewis said, and showed why “we don’t always wake up the same way.”
Still, EEG readings are coarse and can’t probe the deep brain or provide great detail. However, previous studies that used fMRI and electrodes unearthed some of the deeper mechanisms from which such arousal signals might arise. They found that neural signals for waking begin in deep, inner regions of the brain, such as the hypothalamus and the brainstem. These areas wake up the thalamus, which projects the instructions to the cortex.
Though typically faster than falling asleep, waking up can also take some time. Stephan’s sleep signature took a few seconds to travel from the front of the cortex to the back. But recovering consciousness and cognitive abilities, and shedding all sleep inertia, can take minutes to an hour, she said. This study and others also showed that slow waves, usually associated with sleep, can sometimes indicate arousal. The lines are blurry.
Even when we think we’re fully awake and wandering about the world, parts of our brain could be sleeping. This phenomenon, known as local sleep, is thought to occur so that overworked neurons in the brain can rest and be refreshed. It is not unlike how dolphins can sleep with only one brain hemisphere at a time or how some birds sleep on the wing. Sometimes when we’re really tired, some neurons need to refresh and recharge, even if we’re still up and going about our day.
“These people are awake. They have their eyes open. They can be even doing things,” Andrillon said. And yet parts of their brain are undergoing the classic slow waves of sleep. Given that, local sleep challenges what “sleep” actually is.
Troubled Transitions
As we wake up and fall asleep, or even move between sleep states, different types of waves happen at the same time, as neurons synchronize and desynchronize in different regions, in a cacophony of rhythms. This mosaic can lead to experiences such as hypnagogia, lucid dreaming and sleep disorders.
“Sleep disorders are incredibly common,” Lewis said. “They really are often defined by problems with the state switching.”
These disorders might manifest as insomnia, where people don’t fall asleep properly, or as night terrors, sleep paralysis or sleepwalking, where they don’t awaken as expected. In many cases, parts of the brain are awake when they should be sleeping, or vice versa.
Insomnia is fundamentally a difficulty with initiating the transition into sleep or maintaining it. In sleep paralysis, the cortex wakes up before deeper brain regions that control the body, resulting in full consciousness without the ability to move. In paradoxical insomnia, the potential arousal signal Stephan observed in her new study is weak, “so instead of waking them up completely it makes them feel awake,” she said. Her team found the same signal in sleepwalkers, but in those cases it happened “in an inappropriate time window” during deep sleep, she said. They also found that the brain activity of sleepwalkers is similar to that seen during dreaming, suggesting that both states result from similar mechanisms of sleep consciousness.
Decat is continuing to probe what that sleep consciousness looks like. He is running a survey to learn more about the mental experiences people have while falling asleep. Those thoughts and mental images can be hard to remember because to do so, we have to wake up.
Sometimes we wake up right as we’re falling asleep or from the depths of our sleep cycle — times we’re not really supposed to. Maybe it’s a bedmate turning in their sleep that disturbs us. Maybe it’s the clink of keys on a hard floor. Maybe it’s the brain itself, miscalculating when it’s supposed to arouse certain regions.
Your sleep consciousness is disrupted. You pull back from the edge of sleep, and your eyes blink open.
Source link
