The Eye-Opening Truth: How Your Pupils Signal Your Memory Journey

Your pupils convey a lot about you — regarding your emotional state, focus, arousal, and intellect. Quite unexpectedly, they also communicate significantly about your memories. Recent studies in Nature indicate that the size of your pupils while you slumber reveals your thoughts during sleep, illustrating whether you’re reflecting on new memories or recalling older ones.

“It’s like new learning, past knowledge, new learning, past knowledge, and that is slowly fluctuating throughout the slumber,” stated Azahara Oliva, a co-author of the new study and a neuroscientist at Cornell University, in a press announcement. “We are suggesting that the brain has this transitional timescale that distinguishes the new learning from the prior knowledge.”

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Read More: How The Brain Distinguishes Which Memories To Preserve And Which To Forget

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Storing (And Safeguarding) Memories

Researchers have persistently aimed to comprehend the mechanisms behind memory consolidation, which includes the processes that avert “catastrophic forgetting,” where the formation of a new memory obliterates an existing one.

Aiming to gain further insights into these processes, a group of researchers focused on pupil size during non-REM sleep, the sleep phase most associated with memory consolidation. Although the eyes tend to remain still during non-REM sleep, the pupils fluctuate between narrow and broad diameters, reflecting the various substages and depths of slumber during the non-REM period.

“Non-REM sleep is when the genuine memory consolidation occurs, and these moments are very, very brief intervals undetectable by humans, about 100 milliseconds,” Oliva mentioned in the announcement. “How does the brain distribute these rapid screenings of memory throughout the entire night? And how does that segregate the incoming new information, so it doesn’t interfere with the prior knowledge stored in our minds?”

By monitoring the neural activity and pupil size of dozing mice, along with their capability to complete specific tasks once awake, the researchers discovered that new memories are reviewed and solidified when the pupil is smaller during non-REM sleep, whereas older memories are revisited when the pupil is more expansive.

Capturing data with small brain sensors and cameras, these findings elucidate how new memories are retained without displacing older ones, and the timing of this process, which could have significant ramifications for future memory research.

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Read More: What Transpires in Your Brain When You Form Memories?

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Mouse Memory

To reach their conclusions, the team trained mice on numerous tasks over a month, including locating water and food within a maze, and subsequently tracked their brain activity and pupil size during sleep. Over time, the group instructed the mice in an additional task, too, then once again monitored their brain activity and pupil size as they slumbered.

The team interrupted the mice’s slumber when their pupils were either smaller or larger, and later evaluated the mice’s capacity to accomplish their new and past tasks. This enabled the researchers to identify which pupil sizes correlated with the reinforcement of new and older memories.

It was discovered that the mice reactivated their new memories during the non-REM sleep substage when their pupil diameters were smaller and reactivated their prior memories during the non-REM sleep substage when their pupil diameters were larger.

Although further investigations are required to completely understand this process, this study provides crucial insights into the retention of both new and old memories and opens new avenues for memory research. It may inform future memory improvement techniques and therapies for humans.

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Read More: How Naps Enhance Memory Function

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Article Sources:

Our writers at Discovermagazine.com utilize peer-reviewed research and reputable sources for our articles, and our editors assess for scientific precision and editorial standards. Examine the sources utilized below for this article:

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Sam Walters is a journalist reporting on archaeology, paleontology, ecology, and evolution for Discover, alongside a variety of other subjects. Prior to joining the Discover team as an assistant editor in 2022, Sam pursued journalism studies at Northwestern University in Evanston, Illinois.