It’s easy to know when someone is in REM sleep—her eyes move quickly back and forth. Researchers have long known that the movements accompany dreaming, and theorized that the nature of the movements were indicative of some aspect of the dreams. Now researchers have monitored the activity of individual neurons to find that the eye movements are associated with a sort of “scene change” in the dream, they say. The researchers reported their findings this week in Nature Communications.
The researchers took electroencephalograms (EEGs) to monitor the brain activity of 19 patients over four years, both while they were asleep and awake. The scientists were looking at neurons all over the brain, but they were paying special attention to those in the medial temporal lobe. Interestingly, this area of the brain isn’t associated with vision—it’s important for declarative memory, your brain’s conscious recollection of facts and events.
When people were shown a picture, activity in that part of their brains spiked after 3/10 of a second, as their brains recalled all the pertinent facts to put the image in context. When the researchers took EEGs of patients while they slept, they saw similar spikes during REM sleep, implying that brain activity while awake and during REM sleep are quite similar. The eye movements during REM aren’t due to dreams’ visual nature (even babies and people who cannot see move their eyes during REM), but more like moving to the next slide on a slide projector, one of the study authors told the BBC.
This research is an important step towards understanding how the brain works during sleep and dreaming. But it doesn’t answer all the questions—like why our neural wiring allows us to dream at all. The scientists have several theories for how to answer this question, and they hope to pursue them in future work.