A study published in ‘Nature’ shows that changes in pupil size during sleep can indicate whether the brain is recalling new or old memories. Researchers from Cornell University monitored the brain activity of mice and found that pupil constriction during sleep is associated with the consolidation of new memories, while dilation indicates the recall of older ones. The research suggests a complex sleep structure in mice that mirrors humans and may lead to improved memory enhancement techniques and advancements in artificial intelligence training.