A team of Israeli scientists may have discovered why your eyes flicker when you sleep.
Everyone's heard of rapid eye movement (REM) sleep, which often occurs during dreaming.
It's previously been thought that this eye movement could be due to us 'looking around' in our dreams - however, this type of movement also occurs in people who have been blind since birth, and even in fetuses, despite their lack of vision.
Other theories suggest that the fast flickering helps supply oxygen to your cornea, or that it is simply the random result of unconscious brain activity.
The researchers monitored the brain activity of the test subjects using electrodes implanted in their brains
However, a new study conducted by a team of researchers from Tel Aviv university that was published in scientific journal Nature Communications, says that these eye movements accompany a 'change of scene' in our dreams.
By using electrodes to target specific parts of the brain, the researchers found that just after a sleeper's eyes flickered, the part of the brain associated with processing a change in image or concept began to fire.
Dr Yuval Nir, who co-authored the study, told the BBC that the activity of these neurons didn't necessarily correspond with new images, but instead signalled a certain new concept in the brain.
He said: "You can close your eyes and imagine Queen Elizabeth, and these neurons will fire. This activity implies a refresh of the mental imagery and the associations."
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More specifically, the study found that the brain activity that occurs when people are shown an image (especially one linked to a memory) closely corresponds to the kind of activity that occurs just after eye movements in sleeping people.
The research was conducted over the course of four years, with the help of 19 test subjects, all of whom were epilepsy patients who had electrodes already planted in their brains to monitor seizures.
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This theory could help explain why the blind and fetuses show this type of eye movement - it's not necessarily to do with sleepers 'looking around', but instead could be linked to a new concept or image being formed in the brain.
The scientists weren't able to actually figure out what the subjects were dreaming about, but they have gone some way to explaining the reasons behind REM.
Leave the dream-decoding to the UC Berkeley scientists, who in 2011 managed to develop a system that could capture rudimentary images from human brain activity - that could potentially, one day, make it possible for our dream imagery and visual thoughts being reconstructed as digital video.
