Your pupils say a lot about you — about your mental state, your attention span, your arousal, and your intelligence. Somewhat surprisingly, they also say a lot about your memories. According to recent research in Nature, the size of your pupils when you’re asleep reveals what you’re thinking about as you sleep and when, indicating whether you’re ruminating about new memories or about old ones.
“It’s like new learning, old knowledge, new learning, old knowledge, and that is fluctuating slowly throughout the sleep,” said Azahara Oliva, one of the authors of the new research and a neuroscientist at Cornell University, in a press release. “We are proposing that the brain has this intermediate timescale that separates the new learning from the old knowledge.”
Read More: How The Brain Decides Which Memories To Keep And Which To Discard
