Like many other animals, mice enter a world of imagination when they sleep. We know this because their enthralling eyes blink as their brains hum in the key of dreams.
Now, thanks to studies of the brains of sleeping mice, we can say with more confidence why rapid eye movements (REM) occur.
Researchers have been studying the phenomenon of dream-based eye blinking since the 1950s. Sleepers awakening from vivid dreams showed particularly exaggerated eye movements, so it was easy to assume that their eyes were following an imagined scenario instead.
However plausible the claim, it is a difficult hypothesis to support empirically. Most studies to date have relied on waking sleepers’ dreams, which researchers have linked to their eye movements, but this approach leaves a lot of room for doubt.
Other researchers have pointed out that REM sleep can occur in the absence of dreams, especially in young children and in people with brain injuries that may prevent them from dreaming. We can dream without entering REM sleep.
It is important to note that not all studies support what is known as the “trading hypothesis.”
Alternatively, the rapid movements of our eyeballs under their lids, known as saccades, may simply be a neural response to more fundamental activity that occurs when the brain is no longer conscious. does not connect to
To overcome the difficulties of studying the neurology of dreaming humans, scientists at the University of California, San Francisco used mice as a proxy.
Specifically, they measured the activity of nerve cells in the mouse thalamus that are responsible for pointing the head in a certain direction.
In awake mice, saccades are aligned with head movements as mice navigate the real world. Coupling eye movements with neural impulses for head orientation would be important evidence in support of the scanning hypothesis.
The team used tiny implanted probes to record the neural activity of mice, allowing them to freely explore their surroundings while awake. Meanwhile, a series of cameras captured every dart and blink of his eyes.
When the tired test subjects turned over for a nap, the sensors continued recording. Baselines in neural activity and saccades established during periods of wakefulness were used to determine the possibility that eye movements during REM were also related to the direction predicted in their mental world.
Their findings provide clear and objective evidence linking the mouse’s brain control of eye movements and head movements. Just like when you wake up, large, rapid eye movements predict strong changes in head direction as signaled by the thalamus, for example.
Of course, we still have the usual caution in relating the results of an experiment in mice to similar behavior in humans.
Aside from replicating similar precise measurements in a simple human brain, an invasive procedure that is unprecedented in dream research is the most direct proof of a research hypothesis you’ll find.
All of this points to a higher level of coordination in the brain during REM sleep that continues the movement of the body through imagined space.
As well as firmly weighing one aspect of the decades-long debate, the finding may have implications for future research.
According to a commentary by neuroscientists Kathryn Canto and Chris de Zeeuw of the Netherlands Institute of Neuroscience, reading eye movements during sleep could help improve memory or inform treatments for managing trauma.
It can also give us more insight into the purpose of our subconscious wanderings.
“Muscle contractions, which are also frequent during REM sleep, may be related to internal directional cues provided by rapid eye movements, and their analysis may provide further insight into dreams,” Canto and De Zeeuw. Write.
As for what mice can see in their minds while they sleep, we can only imagine in our wildest dreams.
