Human brain regions involved in visual awareness are active during certain periods of sleep, as if the people were awake and seeing images.
Yuval Nir at Tel Aviv University, Israel, and his colleagues monitored brain activity in people with epilepsy who had probes implanted as part of their surgical treatment. The researchers gathered data from the brain region involved in visual awareness as the people slept, viewed familiar images on a computer screen or lay awake in a dark room. They found that brain-activity patterns during rapid eye movement (REM) sleep were similar to those that occurred during image viewing — but not to the brain patterns recorded when participants moved their open eyes while lying in darkness.
The eye movements in REM sleep could be directly linked to dreaming rather than just being an indication of a generally aroused brain, the authors say.