Scientists Reveal What Happens in the Brain When You Daydream

A study has revealed tantalizing clues about what may be happening in the brain when we daydream—a question that neuroscientists are still trying to understand.

While the latest research, published in the journal Nature, was conducted on mice, the authors from Harvard Medical School (HMS) believe the findings could have implications for our understanding of the brain and its cognitive processes.

"We wanted to know how this daydreaming process occurred on a neurobiological level, and whether these moments of quiet reflection could be important for learning and memory," the study's lead author, Nghia Nguyen, a PhD student in the Blavatnik Institute at HMS, said in a press release.

Most brain research focuses on the electrical activity of neurons at the moment when you see or do something.

"The field has learned a lot from this approach, but it doesn't tell us what the brain is doing the rest of the time when you're awake but not actively engaged," Mark Andermann, a senior author of the study at HMS, told Newsweek. "Human neuro-imaging studies and some animal studies suggest there is a lot of brain activity during this time, and that it's organized into patterns of activity where some cells become activity together while others remain quiet."

"But it's been hard to guess exactly what the meaning of these patterns are. This is particularly true in terms of trying to understand why sensory neurons in the [brain's] cortex would still be chattering even at moments when there's nothing 'sensory' in the world to process, such as when you're looking at a blank computer screen. So Nghia Nguyen, a very talented graduate student, and I decided to conduct this research to answer this question by focusing on a part of the brain responsible for visual perception called the visual cortex."

In the study, the researchers monitored the activity of neurons in the visual cortex of mice during experiments in which the rodents were in a quiet waking state.

"I and many other neuroscientists believe that the mouse cortex is quite similar to the human cortex," Andermann said.

The scientists repeatedly showed the mice one of two images, consisting of a different checkerboard pattern featuring gray and dappled black-and-white squares. In between being shown the images, the rodents spent one minute looking at a gray screen.

The team found that when a mouse looked at the two images, neurons in their brain fired in specific patterns for each case. These patterns were sufficiently distinctive that the scientists could discern which image the mouse had looked at from the neural activity.

Furthermore, when a mouse looked at the gray screen between images, the neurons sometimes fired in a similar, but not identical, pattern as when the mouse looked at the image. This was an indication that the mouse was thinking, or daydreaming, about the image, according to the researchers. These daydreams only occurred when the mice were in a relaxed state, the signs of which were calm behavior and small pupils.

Not surprisingly, the mice tended to daydream more about the most recent image they saw. And the researchers also found that they had more daydreams toward the beginning of the day compared to the end—by which point they had already seen each image numerous times.

But then the researchers made a finding that was unexpected. Throughout the day and across days, the patterns of neuron activity observed when the mice looked at the images appeared to change. This phenomenon is known as "representational drift."

Over time, the patterns associated with each image became even more different from one another until the point when each involved an almost entirely distinct set of neurons. Importantly, the pattern observed during a mouse's first few daydreams about an image could be used to predict how the brain's response to that same image would change over time.

The findings of the study suggest that daydreams may be able to shape the brain's future response to what it sees and that these moments during periods of quiet waking could play a role in brain plasticity—the brain's ability to "rewire" itself in response to new experiences. The authors note that these findings are preliminary and need to be explored further in future research.

"When you see two different images many times, it becomes important to discriminate between them. Our findings suggest that daydreaming may guide this process by steering the neural patterns associated with the two images away from each other," Nguyen said.

The latest findings align with a growing body of evidence in rodents and humans indicating that entering a state of quiet wakefulness after an experience can improve learning and memory.

While it remains to be seen whether or not the study's results will be applicable to humans, the researchers suggest that it may be important to make space for moments of quiet wakefulness that can result in daydreams.

"We feel pretty confident that if you never give yourself any awake downtime, you're not going to have as many of these daydream events, which may be important for brain plasticity," Andermann said in the press release.

Offline, quiet moments may allow animals and humans to make sense of the world by linking previous experiences to their overall understanding of how the world works, according to Andermann.

While a lot of memory consolidation and updating of models of how the world works has been believed to occur in humans and other animals during sleep, recent work suggests that similar processes may happen during moments of quiet waking.

"This may even provide an opportunity for a different kind of mental exploration of the previous events than during dreaming that occurs during sleep—which may also allow a different kind of learning about recent experiences during quiet waking than during sleep," Andermann told Newsweek.

"This also suggests that some amount of daydreaming is possibly beneficial to learning and memory and that we might want to look up from our phones to the sky from time to time and just let our thoughts flow to whatever the brain wants to process about recent experiences.

Update 1/24/24, 10:44 a.m. ET: This article has been updated with comment from Mark Andermann.