Man daydreaming, happy sitting at work desk

A man working from home (© fizkes - stock.adobe.com)

CAMBRIDGE, Mass. — What happens to our brains while we stare out the window daydreaming? Even though daydreaming has gone largely unexplored by neuroscientists, a new study conducted by Harvard Medical School (HMS) researchers is shining light on a phenomenon experienced by nearly everyone.

The team tracked the activity of neurons in the visual cortex of the brains of mice in a relaxed, awake state. They discovered that these neurons occasionally fired in patterns similar to those seen when the mice were actually looking at an image. This suggests that the mice were potentially daydreaming about the image. Intriguingly, the patterns of neuron activity during the initial daydreams could predict how the brain would respond to the image over time.

“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,” says study lead author Nghia Nguyen, a PhD student in neurobiology at the Blavatnik Institute at HMS.

The study’s focus on the visual cortex is notable, as most research on neuron replay and memory formation has centered on the hippocampus, the brain region responsible for memory and spatial navigation.

“My lab became interested in whether we could record from enough neurons in the visual cortex to understand what exactly the mouse is remembering — and then connect that information to brain plasticity,” says study senior author Mark Andermann, a professor of medicine at Beth Israel Deaconess Medical Center and professor of neurobiology at HMS.

In their experiment, researchers showed mice two different checkerboard patterns and recorded the activity of around 7,000 neurons in the visual cortex. They found that when the mice looked at a blank gray screen between the images, their neurons sometimes fired similarly to when they saw the image, indicating daydreaming.

During the experiments, mice repeatedly looked at one of two images, shown here, with one-minute breaks in between.
During the experiments, mice repeatedly looked at one of two images, shown here, with one-minute breaks in between. The images were selected based on their ability to elicit a strong response from neurons in the visual cortex. (Video: Andermann lab)

These daydreams were more frequent early in the day and tended to focus on the most recently seen image. Over time, the neuron patterns for each image diverged significantly, a phenomenon the researchers call “representational drift.” This drift wasn’t random; the early daydreams about an image helped predict how the brain’s response to that image would change.

Moreover, these daydreams in the visual cortex coincided with replay activity in the hippocampus, suggesting communication between these two brain regions during daydreaming.

The study suggests that daydreaming may play a role in brain plasticity, helping the brain to distinguish between different images or experiences. Nguyen speculates that daydreaming could be important for the brain’s ability to respond more specifically to different stimuli in the future.

“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,” explains Nguyen.

Between images, mice spent a minute looking at a gray screen
Between images, mice spent a minute looking at a gray screen. During this time, neurons in the visual cortex of the brain, shown here, occasionally fired in a pattern similar to one seen when the mice were looking at an image, suggesting that mice were daydreaming about the image. (Video: Andermann lab)

This research aligns with other studies indicating that quiet wakefulness after an experience can enhance learning and memory. The team plans to further explore how neuron connections in the visual cortex change when the brain processes an image.

While it remains to be seen if human daydreaming involves similar processes, preliminary evidence suggests that recalling visual imagery activates the visual cortex and hippocampus in humans as well. For now, researchers believe that allowing time for daydreaming and quiet reflection could be crucial for brain health and learning.

“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,” concludes Andermann.

The study is published in the journal Nature.

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2 Comments

  1. PJ London says:

    So why do they call it ADHD and prescribe drugs to cure it?

  2. Glenn says:

    Do daydreams have a survival value or a sexual advantage? Do nocturnal dreams have a survival value or sexual advantage? Or maybe they have no value and are just “ride along” and have no value except for a psychoanalyst.