Study Reveals Role of Eye Pupils in Memory Retention During Sleep

The study involved mice that were trained to perform tasks, such as locating water or cookies in a maze, over a month. After training, these mice were equipped with brain electrodes to monitor neural activity and tiny cameras tracking their pupil changes while they slept.

The research specifically focused on non-REM (non-rapid eye movement) sleep, a phase known for consolidating memories. The results showed that during this phase, pupil size fluctuated subtly—sometimes shrinking and at other times widening—tying these changes to precise brain activities. When the pupils contracted, the mice’s brains replayed recently learned memories, aiding in the storage of new knowledge. Conversely, during pupil dilation, older memories were revisited.

This back-and-forth mechanism prevents interference between new and existing information, helping the brain avoid the problem of “catastrophic forgetting,” where new learning might overwrite older memories.

Assistant Professor Azahara Oliva noted that previous assumptions regarded non-REM sleep as a uniform process, but this study unveils a nuanced micro-structure within it. The tiny pupil adjustments, which occur in very brief intervals of around 100 milliseconds, facilitate a rhythm for managing both new and old memories.

To validate their findings, researchers disrupted the mice’s sleep at various points and tested their memory recall afterward. The results confirmed that sleep interruptions during the pupil-contracted phase hindered recollection of new tasks, while disturbances during the pupil-dilated phase affected older task reminders. This indicates that timing is crucial for memory consolidation.

Although the study was conducted with mice, its implications could be significant for humans. Understanding how pupil dynamics influence memory might lead to improved learning strategies, memory recovery methods, and even advancements in artificial intelligence that mitigate issues related to memory overwrite.

Assistant Professor Antonio Fernandez-Ruiz underscored the potential of their findings to shed light on the different responses of the brain in sorting and retaining memories. Future research may explore whether similar processes exist in humans, potentially using eye-tracking technology to enhance memory and learning.

Overall, this study emphasizes the importance of quality sleep, suggesting that the brain is actively engaged in complex tasks to manage and protect memories while preparing for future learning.