Mouse enter a world of imagination when they sleep. Their eyes flicker back and forth as their brain hums in the key of dreams.
Thanks to a study on the brains of sleeping rodents, we now know why REM occurs.
Since the 1950s, researchers have studied dream-based eye twitching. It was easy to assume that the eyes were keeping track of the make-believe scenery in the dream because of the exaggerated eye movements the sleepwalkers displayed.
It's not easy to support a hypothesis like this. Most studies have relied on awakened sleepers self- reporting their dreams, but that approach leaves a lot of room for doubt.
In people with brain trauma, REM sleep can occur in the absence of dreams, as well as in young babies. We are1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556
The scanning hypothesis is not backed up by all studies.
The saccades are described as a nervous response to more fundamental activity that occurs when the brain is no longer tethered to consciousness.
Scientists from the University of California, San Francisco used mice as a proxy to study the brain.
The activity of nerve cells in the mouse thalamus was measured.
Saccades line up with head movements in awake mice. The scanning hypothesis hinges on matching eye movements with nervous impulses for head direction.
Using small implanted probes, the team was able to record the neural activity of the mice while they were awake. Their eyes were captured by a series of cameras.
The test subjects were tired when they fell asleep. The eye movements during REM were used to determine how likely they were to be related to their intended direction through their mental world.
The results show that the mouse's eye movements and brain's control over head movements are connected. Bigger eye movements predict stronger changes in head direction as directed by the thalamus.
There is a caveat to connecting the results of an experiment on mice with the same behavior in humans.
It's the most direct evidence for the scanning hypothesis, because it's short of replicating similar precise measures on a convenient human brain.
There is a higher level of coordination across the brain during REM sleep that allows a body to move through an imagined space.
The discovery could have implications for further research, since it weighed in on one side of the debate.
Eye movements during sleep can be used to inform therapies for improving memory or managing trauma.
It could help us understand the purpose of our wanderings.
"Muscle twitches, which also frequently occur during REM sleep, might be related to the internal heading cues provided by rapid eye movements, and analyses of these might give further information about dreams," they wrote.
We can only imagine what it is that mice see as they sleep.
The research was published in a scientific journal.
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