Cornell University researchers have uncovered a surprising link between pupil dynamics and the brain’s process of creating and storing long-lasting memories.
By studying mice, they found that pupil changes during non-REM sleep help distinguish between consolidating new memories and revisiting older ones.
This separation prevents the brain from overwriting past knowledge when forming new memories, a phenomenon known as “catastrophic forgetting.”
The study, led by assistant professors Azahara Oliva and Antonio Fernandez-Ruiz and published in Nature, sheds light on the intricate timing and structure of memory processing during sleep. It also offers potential applications for improving human memory and training artificial neural networks.
Over a month-long experiment, the researchers trained mice to complete various tasks, such as navigating a maze to earn water or cookie rewards. Afterward, the mice were fitted with brain electrodes to monitor neural activity and tiny cameras to track pupil changes.
The setup allowed the researchers to observe the interplay between brain activity and pupil behavior during non-REM sleep, a phase when memories are solidified.
The team discovered that during a specific substage of non-REM sleep, the mice’s pupils shrank, signaling the brain was consolidating new memories learned earlier that day.
In another substage, when the pupils dilated, the brain revisited older memories. This alternating pattern of activity ensures that new information is integrated without disrupting the storage of past knowledge.
“Non-REM sleep is when the actual memory consolidation happens, and these moments are very, very short—about 100 milliseconds,” explained Oliva. “The brain separates these bursts of memory replay across the night, keeping new knowledge from interfering with what we already know.”
The researchers tested their findings by interrupting the mice’s sleep at different moments and later evaluating how well the animals remembered their tasks.
Disruptions during pupil-shrinking phases impaired the recall of new tasks, while interruptions during pupil-dilating phases affected older memory retention. This demonstrates the brain’s remarkable ability to manage memory processing on different timescales during sleep.
The study also revealed that the temporal structure of mice’s sleep is more complex than previously believed, resembling human sleep stages. This complexity helps the brain efficiently manage the enormous task of sorting and storing memories.
Oliva described the brain’s process as a rhythmic fluctuation: “It’s like new learning, old knowledge, new learning, old knowledge, cycling slowly through the sleep.”
The team proposes that the brain uses this intermediate timescale to maintain a clear distinction between what’s recently learned and what’s already stored.
These findings could have far-reaching implications. For humans, understanding how the brain manages memory consolidation could lead to improved techniques for boosting memory or addressing memory-related disorders.
In technology, the insights may inspire better algorithms for artificial neural networks, helping them learn new information without overwriting previously acquired data.
Although the research offers fascinating insights, it has limitations. The study focused on mice, and while their sleep patterns share similarities with humans, further research is needed to confirm whether the same mechanisms occur in people.
Additionally, the practical applications for memory enhancement or neural network design will require more exploration. Nevertheless, this study provides a compelling glimpse into how the brain’s coordination of sleep and memory may hold the key to unlocking new possibilities in neuroscience and beyond.
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The research findings can be found in Nature.
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