Rapid eye movements in sleeping mice match where they look in their dreams, new research shows

eyes closed

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Do rapid eye movements during sleep reveal where you are looking in the dreamscape, or are they just the result of random twitching of our eye muscles? Since the discovery of REM sleep in the early 1950s, the significance of these rapid eye movements has intrigued and fascinated dozens of scientists, psychologists and philosophers. REM sleep, as the name suggests, is a period of sleep during which your eyes move under your closed eyelids. This is also the period when you have intense dreams.

We are researchers who study how the brain processes sensory information during wakefulness and sleep. In our recently published study, we found that the eye movements you make while you sleep may reflect where you are looking in your dreams.

measuring dreams

Previous studies have tried to answer this question by monitoring people’s eye movements while they sleep and waking them up to ask them what they were dreaming about. The aim was to find a possible connection between the content of a dream just before waking up (for example, a car coming from the left) and the direction in which the eyes were moving at that time.

Unfortunately, these studies have produced conflicting results. Some participants may have reported dreams inaccurately, and it is technically difficult to match a given eye movement to a specific time in a self-reported dream.

We decided to circumvent the problem of self-declaration of dreams. Instead, we used a more objective way to measure dreams: the electrical activity of a sleeping mouse’s brain.

Mice, like humans and many other animals, also experience REM sleep. Also, they have a sort of internal compass in their brain that gives them an idea of ​​the direction of the head. When the mouse is awake and running, the electrical activity of this internal compass accurately signals the direction of its head, or “heading”, as it moves through its environment.

Interestingly, a previous study showed that this internal compass is active during REM sleep. But instead of pointing out the real, fixed direction of the motionless sleeping mouse’s head, the internal compass continued to move as if the mouse were awake, running through the virtual environment of its dreams.

Dreams occur during REM sleep.

Eye movements and head movements are tightly coupled during wakefulness. This means that when people and mice move their gaze, their heads and eyes turn in the same direction. We reasoned that if eye movements during REM sleep reveal changes in gaze in the dream world, these eye movements should occur at the same time and in the same direction as changes in heading in the sleeping mouse brain.

To test this hypothesis, we measured rapid eye movements, or saccades, when mice were awake and mapped them to the electrical activity of their brain’s internal compass. We then monitored the eye movements of sleeping mice during REM sleep with miniature cameras placed in front of both eyes. Because mice often don’t fully close their eyelids while sleeping, this allowed us to precisely measure the direction of their eye movements. Similar to when the mice were awake, we recorded the electrical activity of their brain’s internal compass to decode course changes during REM sleep.

Strikingly, we found that the direction of eye movements in sleeping mice corresponded precisely to changes in direction, just like gaze changes in awake mice. This means that eye movements during REM sleep can reveal shifts in gaze in the virtual dream world, providing a window into the cognitive processes occurring in the dream brain.

The Dreaming Brain

Our study shows that during REM sleep, the part of the brain that controls the sense of head direction coordinates with the part that controls eye movement. This finding may just be the tip of the iceberg for how separate parts of the brain work together during sleep.

If other areas of the brain are also working together during REM sleep, such as those responsible for sensory perception, emotion, or sense of place, this overall coordination between the parts may well be the basis for vivid and vivid dream experiences. realistic.

When you’re awake, your sense of head direction relies on information gathered from several areas of the brain involved in your sense of balance and sight, among other things, which are active when you move. Our study raises an important question: What does your sense of head direction rely on during REM sleep, when you’re not moving?

Our next steps are to determine what moves the brain’s internal compass during REM sleep, how it moves with the eyes, and how the different senses work together to generate the realistic experience of dreams.

Eye movements in REM sleep mimic gazes in the dream world

Provided by The Conversation

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