Seeing an imaginary scene (Image: Victor Habbick Visions/Getty)

Your body may be still, but as you dream, your eyes can flicker manically. The rapid eye movement stage of sleep is when we have our most vivid dreams – but do our flickering eyes actually “see” anything?

It is a question psychologists have been asking since REM sleep was first described in the 1950s, says Yuval Nir at Tel Aviv University in Israel. “The idea was that we scan an imaginary scene,” says Nir. “It’s an intuitive idea, but it has been very difficult to provide evidence for it.”

Until now, much of the evidence has been anecdotal, says Nir. “People who were woken up when their eyes were moving from left to right would say they were dreaming about tennis, for example,” he says.


More evidence comes from a previous study that monitored the sleep of people who have a disorder that means they often physically act out their dreams. Their eye movements matched their actions around 80 per cent of the time – a man dreaming about smoking, for example, appeared to look at a dream ashtray as he put out a cigarette.

But most of the REM sleep these people had was not accompanied by body movements, making it hard to know for sure. And other researchers have argued that the eye flickers can’t be linked to “seeing” anything because rapid eye movements happen in both fetuses and people who are blind – neither group would have experience of vision and so wouldn’t be expected to move their eyes to follow an object, for example.

In the mind’s eye

To investigate further, Nir and his colleagues monitored people who have epilepsy and have electrodes implanted deep into their brains to help with treatment.

These electrodes were mostly in the medial temporal lobe, a region that responds strongly to pictures, and allowed the team to record the activity from around 40 neurons in each volunteer’s brain as they slept. They found that activity seemed to spike around a quarter of a second after an eye flicker, just as it did when the volunteers saw an image when awake. “It is very plausible that they are looking at a dream image,” says Nir.

“It is extremely interesting… that these eye movement produce something like visual processing during dreaming,” says Michael Czisch at the Max Planck Institute of Psychiatry in Munich, Germany. He thinks we might see visual scenes as a side effect of when memories are replayed during sleep.

Because the researchers didn’t wake their volunteers, they can’t be sure what they were dreaming, Nir says. “But we are sure that the brain is alternating between different mental imagery,” he says. “Every time you move your eyes, a new image forms in the mind’s eye.”

Journal reference: Nature Communications, DOI: 10.1038/ncomms8884