REM sleep the key to dream imagery
Now research into epilepsy patients suggests that the flickering eyes are actually "viewing" a dream image, having triggered the parts of the brain used to process visual images while we are awakes.
Michael Czisch at the Max Planck Institute of Psychiatry in Munich, told New Scientist that he thinks we might see visual scenes as a side effect of when memories are replayed during sleep.
“It is extremely interesting… that these eye movement produce something like visual processing during dreaming,” he told the magazine.
Neuroscientist Yuval Nir of Tel Aviv University and colleagues studied patients undergoing treatment for severe epilepsy that led to the discovery of electrical activity in the brain's vision centre.
By monitoring electrical activity while the patients were asleep and matching it to eye movements, they found that rapid eye movement was immediately followed by a burst of electrical activity in the medial temporal lobe where visual images are processed when we are awake.
Nir told the ABC that the activity in these neurons during rapid eye movement sleep suggests that new images or concepts are being formed in the mind's eye while we dream.
"It may be, for example, that those particular moments that our eyes move, it's like a reset of brain activity, it glitches to the next slide of a dream," he said.
An understanding of the process may help explain how sleep helps the learning and memory process, he said.
"These moments may represent privileged windows of opportunity to look more closely at what exactly is happening during sleep," Nir told the broadcaster.
The research has been published in the journal Nature Communications.