Medical Research Council - London Institute of Medical Sciences

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Mouse pupil filmed fluctuating overnight, matching its sleep state. A potential approach for monitoring sleep and insomnia

21 September 2018

Studying Pupils

Have you ever seen someone’s pupil suddenly shrink when the lights turn on in a dark room? Our pupils change size constantly throughout the day, adjusting to light levels and responding to shifts in attention. But what happens at night? Hidden behind closed eyelids, sleeping pupil activity has always been a mystery. Now researchers have managed to film a mouse’s pupil overnight. An infrared light shines on the back of the eye, making the pupil glow white on an infrared camera. The recordings revealed that pupil size fluctuates, precisely matching the state of sleep at any given time. The deeper the mice’s slumber, the narrower the pupils, suggesting they’re blocking out intrusive light during important deep sleep – thought to be the key time for memory consolidation. Furthermore, tracking pupils is a new approach to monitoring sleep, so could one day help people plagued by insomnia get a good night’s rest.

Written by Anthony Lewis

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