Why Old Memories Survive New Ones

Why don’t new memories overwrite old ones? Sleep science holds clues

https://www.nature.com/articles/d41586-024-04232-1

By Traci Watson

When we sleep, our brains do an incredible balancing act, keeping old memories intact while making space for new ones. A groundbreaking study, published in Nature, reveals how this works in mice: different sleep stages handle different memory tasks. During deep sleep, small-pupil phases focus on encoding new memories, while large-pupil phases help preserve older ones. Scientists found that disrupting brain activity during the small-pupil phase caused mice to forget new memories, but their older memories stayed safe. The reverse held true during the large-pupil phase. These findings could have big implications for humans and even for artificial intelligence, which faces similar challenges in managing new and old data.