What happens in the brain while we are daydreaming?

Researchers have made significant strides in understanding brain activity during daydreaming. The study, conducted on mice, offers insights that could illuminate similar processes in humans.

The research was led by Nghia Nguyen, a PhD student in Neurobiology at the Blavatnik Institute at Harvard Medical School. The team tracked the activity of neurons in the visual cortex of mice while they were in a relaxed waking state. 

Moments of quiet reflection 

The experts discovered that these neurons occasionally fired in patterns resembling those observed when the mice viewed actual images. 

“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,” Nguyen explained.

The role of the visual cortex 

This study ventured beyond the hippocampus, a region extensively studied for memory and spatial navigation, to focus on the visual cortex’s role in forming visual memories.

”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,” said senior author Mark Andermann, a professor of Medicine at Beth Israel Deaconess Medical Center and of Neurobiology at HMS.

Distinct neural patterns 

In their experiments, the researchers showed mice two different checkerboard images and recorded neural activity from around 7,000 neurons in the visual cortex. 

The experts found distinct neural patterns for each image and similar but not identical patterns when the mice viewed a gray screen, suggesting the mice were daydreaming about the images. The daydreams correlated with a state of relaxation, indicated by calm behavior and small pupils.

Representational drift 

Surprisingly, the study revealed that the daydreams could predict future changes in the brain’s response to images, a phenomenon known as “representational drift.” 

“There’s drift in how the brain responds to the same image over time, and these early daydreams can predict where the drift is going,” Andermann said.

The team also observed that these daydreams in the visual cortex coincided with replay activity in the hippocampus, hinting at communication between these two brain regions.

Broader implications

The findings suggest that daydreaming may play a role in brain plasticity, aiding in distinguishing between different experiences. “Our findings suggest that daydreaming may guide this process by steering the neural patterns associated with the two images away from each other,” Nguyen explained.

The researchers plan to further explore the connections between individual neurons in the visual cortex and how these connections evolve. Andermann reflects on the broader implications of their work: “We were chasing this 99 percent of unexplored brain activity and discovered that there’s so much richness in the visual cortex that nobody knew anything about.”

Human daydreaming

While it remains to be confirmed if similar patterns occur in human daydreaming, preliminary evidence suggests an analogous process. Studies have shown increased brain activity in the visual cortex when people recall images, aligning with these recent findings in mice.

The study underscores the potential importance of quiet wakefulness and daydreaming in both humans and animals for learning and memory. “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 concluded.

The study is published in the journal Nature.

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