When you close your eyes in bed tonight, something strange will happen to you. Your mind passes from ordinary thoughts to dreams, but it is impossible to say exactly when it happened. We tend to imagine that there is a clear line between when we are asleep and when we are awake. I think when I’m awake. We dream when we are asleep. But our research, published in Cell Reports, shows that this boundary is more porous than we imagined. You can dream before you fall asleep and plan your day after you fall asleep.
From thoughts to dreams and everything in between
Think about what it means to be awake. Now, as you read these lines, sounds reach you, light falls on you, and fabric touches your skin. You are fixed in the world. Sleep is the opposite. You are still, cut off from the outside world, living in an experience that is constructed from within – a dream.
There is a passage of time between the two. You don’t switch from one state to another like turning on a light switch. This is a gradual transition in which brain activity decreases, muscles relax, and breathing deepens. And the mind does not stop functioning. It takes other forms by producing thoughts, fleeting images, some pieces of music, dream pieces, etc. related to that day or the day beyond. Researchers call this half-awake, half-asleep state of consciousness “hypnosis.”
The problem is that these experiences are temporary, ever-changing, difficult to report, and even harder to categorize. How do I transition from “What shall I eat tomorrow?” Until “I’m sitting on a train moving underwater”? Until now, researchers have tried to classify it into categories based on what it is (“This seems weird, it must be a dream”) or when it happens (“I rule out anything that happens during wakefulness”).
As a result, although we knew that many experiences passed through the mind during the hypnagogic period, it was unclear which experiences were produced in the brain, when and how. That’s exactly what we’re trying to understand.
Let the data speak for itself
To get a clearer picture, we needed to abandon predefined categories and let the data speak for itself. We used electroencephalography (EEG) to record the brain activity of 103 participants while they took a nap in the lab. Electrodes were placed across the scalp to capture nerve signals, allowing researchers to distinguish between wakefulness (fast alpha waves) and light sleep (slow theta and sigma waves with sudden, very slow waves and short rhythmic bursts called sleep spindles).
We interrupted them several times by making noise and asked very simple questions. “What was going through your mind right before the alarm went off?” We then asked them to rate their experience along four dimensions. It is how strange (and extraordinary) it is, how fluid and continuous (or, on the contrary, fragmentary), how spontaneous (lack of voluntary control) it is, and the impression of being awake or asleep.
We collected a total of 375 experiences during the sleep onset period. Rather than deciding for ourselves what counts as a dream or a waking thought, we used machine learning algorithms to group these experiences into “mental states” without defining in advance what they should be.
Taking into account participants’ ratings on all four dimensions, the algorithm searched for groups of experiences that were similar to each other, as if searching for “families” on a four-coordinate map. Broadly speaking, these are memory fragments (“I had an image of my father in my head”), thoughts about my surroundings (“I was hearing sounds in the street”), dream-like images (“I was seeing little aliens”), and deliberate introspection (“I was thinking about what I was going to do tomorrow”).
The next question arose naturally. At what point during wakefulness and sleep does each of these states occur?
I dream when I’m awake and think when I’m asleep.
Here you will find surprising results. We expected a simple scenario where we think rationally when awake and have strange images during sleep. And some patterns have actually gone in that direction. As people slept through the night, their mental states connected to their surroundings and to deliberate introspection diminished.
But here is the crux of our findings. All four states were present across the board: waking, falling asleep (stage N1), and more established sleep (stage N2). What passes through our mind does not depend on whether we are awake or asleep.
In fact, there are cases that turned out to be frankly paradoxical. One participant who was fully awake (alpha waves on the brain waves, a sign of arousal) reported that “ants were climbing on me with a crossword puzzle in the background.” Another participant sleeping at stage N2 (sudden large slow waves on the EEG recording, a typical indicator of sleep) simply said, “I was thinking about work.” We dream before we fall asleep. We reflect while we sleep.
There is one point that still needs to be clarified. That is, the brain does not function the same way during wakefulness and sleep. During sleep, it slows down and synchronizes. So how do dream-like experiences occur during wakefulness and sleep? To understand this, we focused on a shorter time window to capture rapid changes in brain waves, 64 electrodes to precisely cover the cortex, and finer-grained brain signal metrics than previously used.
We have discovered brain signatures that indicate mental states. For example, in dream-like imagery, communication between distant brain regions was weakened, as if these regions of the brain were less able to talk to each other. The important point is that these signatures are the same whether a person is awake or asleep. In other words, the brain can produce the same kind of mental experience regardless of the state of alertness.
what about you? What goes through your mind when you fall asleep? These results raise an equally interesting question: Do all people have the same mental experiences? In the same order? And does this tell us anything about who we are?
To find out, we designed Drifting Minds, a roughly 20-minute online survey that explores your mental experiences during the hypnagogic phase. Nearly 5,000 people from five continents have already participated. The goal is to identify a population’s sleep onset profile and see whether it is age-, gender-, and culture-dependent, as well as associated with traits such as creativity, anxiety, mental imagery, and sleep quality.
At the end of the survey, you can discover your own sleep onset profile and compare yourself to others. Join us here!
Deep down, what we’re trying to do is understand what the brain produces in this “in-between” zone and what it tells us about us. So tonight, when you close your eyes, you’ll walk through that strange hallway once again. Pay attention to the moment and what is going on in your mind right before you drift off…
This article is republished from The Conversation under a Creative Commons license. Read the original article.
