Eye movements in REM sleep mimic gazes in the dream world

According to a recent study by researchers at UC San Francisco, when our eyes move during REM sleep, we are looking at objects in the dream world that our brains have constructed. The research provides insight into how our imaginations function as well as how we dream.

Since the 1950s, it has been recognized that the stage of sleep during which dreams take place is known as REM sleep, named after the rapid eye movements that are linked with it. But there is still a lot of ambiguity and disagreement about the reason for the eye movements.

"We demonstrated the consistency of these eye movements. They coordinate with what is occurring in the mouse's virtual dream world, "Massimo Scanziani, PhD, the study's senior author, who is quoted in Science on August 25, 2022.

"This discovery answers a riddle that has piqued the interest of scientists for decades and gives us a glimpse into the ongoing cognitive processes in the sleeping brain," he said.

However, there were few ways to test this theory, and the experiments that could be done (noting a dreamer's eye direction and then waking them up to ask where they were looking in the dream) produced contradictory results. In the second half of the 20th century, some experts hypothesized that these REM movements may be following scenes in the dream world. Many scientists dismissed REM movements as random activities, possibly performed to keep the eyelids moist.

Scanziani and Yuta Senzai, PhD, a postdoctoral researcher at UCSF, were able to examine "head direction" cells in the brains of mice, which also undergo REM sleep, thanks to significantly more sophisticated technology. Researchers can determine the mouse's perceived direction by looking at the activity of these cells, which function somewhat like a compass.

The team concurrently tracked the mouse's eye movements and recorded information about the mouse's heading directions from these cells. Comparing them, scientists discovered that the mouse's internal compass and eye movements during REM sleep were precisely aligned, just as they are when the mouse is awake and moving around.

Scanziani is fascinated by the "generative brain," or the capacity to conjure up scenarios and objects.

"This ability to connect our real-world experiences with other things that don't exist at the present time and may never exist," he said, "is one of our assets as humans." Our brain's capacity for creation serves as the foundation for our creativity.

It is challenging to investigate this kind of brain activity since it necessitates observing the brain as it forms new memories and concepts in the absence of sensory input. Dreaming gives us the chance to do that.

Scanziani observed that one can mix the recognizable with the impossible in a dream. He talked about having a recurring dream as a young diver in which he could breathe underwater. He always discovered it wasn't true when he awoke. However, Scanziani explained, "in the dream, you think it to be genuine since there aren't sensory inputs to bring you back to reality." It's a flawlessly peaceful fictional planet.

The findings of Scanziani's team support the notion that dreams are a means of integrating information received during the day because they show that the same brain regions, of which there are many, cooperate during both awake and dreaming.

Scanziani intends to keep working to solve the puzzle of how those brain areas interact to develop this generative power.

It's critical to comprehend how the brain alters itself as a result of life experiences, he said. We can gain insight into how those experiences become a part of our individual conceptions of what the world is like and how it functions by understanding the mechanisms that allow us to coordinate so many different brain regions when we sleep.

University of California - San Francisco