You’re sitting quietly, and suddenly your brain tunes out the world and wanders to something else entirely perhaps a recent experience, or an old memory. You just had a daydream. Yet despite the ubiquity of this experience, what is happening in the brain while daydreaming is a question that has largely eluded neuroscientists.
Now, a study in mice, published December 13 in “Nature”, has brought a team led by researchers at Harvard Medical School one step closer to figuring it out.
The researchers tracked the activity of neurons in the visual cortex of the brains of mice while the animals remained in a quiet waking state. They found that occasionally these neurons fired in a pattern similar to one that occurred when a mouse looked at an actual image, suggesting that the mouse was thinking or daydreaming about the image. Moreover, the patterns of activity during a mouse’s first few daydreams of the day predicted how the brain’s response to the image would change over time.
The research provides tantalizing, if preliminary, evidence that daydreams can shape the brain’s future response to what it sees. This causal relationship needs to be confirmed in further research, the team cautioned, but the results offer an intriguing clue that daydreams during quiet waking may play a role in brain plasticity, the brain’s ability to remodel itself in response to new experiences.
An Overlooked Brain Region
Scientists have spent considerable time studying how neurons replay past events to form memories and map the physical environment in the hippocampus, a seahorse-shaped brain region that plays a key role in memory and spatial navigation.
By contrast, there has been little research on the replay of neurons in other brain regions, including the visual cortex. Such efforts would provide valuable insights about how visual memories are formed.
As per a senior author Mark Andermann, professor of medicine at Beth Israel Deaconess Medical Center, and professor of neurobiology at HMS, his lab became interested in whether it 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.
In the new study, the researchers repeatedly showed mice one of two images, each consisting of a different checkerboard pattern of gray and dappled black and white squares. Between images, the mice spent a minute looking at a gray screen. The team simultaneously recorded activity from around 7,000 neurons in the visual cortex.