A recent study has uncovered that pupil size fluctuates during sleep, reflecting different levels of brain activity. Researchers developed a method to monitor pupil dynamics in sleeping subjects by keeping their eyes open with a special adhesive. The study demonstrated a correlation between pupil size changes, sleep stages, and brain wave patterns. This finding suggests the brain remains active and dynamic during sleep. Scientists believe monitoring pupil dynamics may serve as a diagnostic tool for sleep disorders and neurological conditions. Future studies will examine if a region in the brainstem known as the locus coeruleus is responsible for the changes in pupil size.

https://neurosciencenews.com/sleep-pupil-brain-activity-28464/