Eye movements during REM sleep mimic gaze during dreams, according to a new study.
Multiple brain regions coordinate to conjure fully imagined worlds
When our eyes move during REM sleep, we are observing the dream world created by our brains, according to a new study by researchers at the University of California, San Francisco (UCSF) something. These findings reveal not only how we dream, but also how our imaginations work.
REM sleep, named for the rapid eye movements associated with it, has been known since the 1950s to be the stage of sleep in which dreams occur. However, the purpose of eye movements remains a mysterious and controversial issue.
REM sleep first occurs about 90 minutes after falling asleep. Your eyes move rapidly from side to side behind closed eyelids. The mixed frequency brainwave activity is getting closer and closer to what is seen while awake. Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near-awake levels. Most dreams occur during REM sleep, although some may also occur during non-REM sleep. Your arm and leg muscles are temporarily paralyzed, which prevents you from achieving your dreams. As you age, the amount of time you spend in REM sleep decreases.
"We show that these eye movements are not random. They are coordinated with what is happening in the mouse's virtual dream world," said Dr. Massimo Scanziani, senior author of the study, which appears in the August 25, 2022 issue of Science magazine.
"This work gives us a glimpse into the cognitive processes underway in the sleeping brain while solving a puzzle that has piqued scientists' curiosity for decades," he said.
Linking eye movements to dream direction
In the second half of the 20th century, some experts hypothesized that these REM movements might follow scenes from the dream world. However, there are few ways to test this theory, and the experiments that can be done (noting the direction in which dreamers look, then waking them up and asking them where they are looking in their dreams) provide conflicting results. Many scientists view REM movements as random movements, perhaps to keep the eyelids lubricated.
With more advanced technology, Scanziani and UCSF postdoctoral researcher Yuta Senzai, Ph.D., were able to look at "head direction" cells in the brains of mice that also experienced REM sleep. These cells behave like a compass, and their activity shows scientists which direction the mice think they are heading.
While monitoring the mice's eye movements, the team simultaneously recorded data from these cells about their orientation. Comparing them, they found that the direction of eye movements and the direction of the mouse's internal compass were precisely aligned during REM sleep, just as they were when the mouse was awake and moving around.
A false world of perfect harmony
Scanziani is interested in the "generative brain", the ability to compose objects and scenes.
"One of our strengths as humans is the ability to combine our real-world experiences with other things that don't exist now and may never exist," he said. "This generative ability of our brains is the basis of our creativity.
However, studying this type of brain function is difficult because it requires studying the brain while it develops new experiences without sensory input and Ideas. Dreaming provides such an opportunity.
Scanziani points out that in dreams. In, you can combine the familiar with the impossible. He describes a recurring dream he had as a young man in which he was able to breathe underwater, which he always woke up to and found out it wasn't true. But in a dream, you believe it to be real because there is no sensory input to bring you back to reality," Scanziani said. "It's a false world of complete harmony.
Scanziani's team found that the same parts of the brain - and there are many of them - are coordinated during dreaming and waking, lending credence to the idea that dreams are a way of integrating information gathered throughout the day.
How these brain regions work together to produce this generative ability is a mystery that Scanziani plans to continue trying to unravel.
"It's important to understand how the brain updates itself based on accumulated experience," he said. "Understanding the mechanisms that allow us to coordinate many different parts of the brain during sleep will give us insights into how these experiences become part of our personal model of what the world is and how it works.
