This is how memories are formed: what happens to pupils during sleep

Scientists from Cornell University (New York, USA) have found that pupil size is the key to understanding how and when the brain forms strong, long-term memories. The research was conducted on mice.

The mice were equipped with brain electrodes and tiny cameras to track their eyes. Scientists found that new memories are reactivated and consolidated when the pupil shrinks during REM sleep. When the pupil dilates, the process is repeated for old memories, MedicalXpress writes.

According to the scientists, it is this ability of the brain to separate the two stages of sleep using a previously unknown microstructure that prevents "catastrophic forgetting" when the consolidation of one memory erases another.

"The findings could lead to better memory enhancement techniques for humans and may help computer scientists train artificial neural networks to be more efficient," the researchers write in the study, which was published in the journal Nature.

The study showed that the temporal structure of sleeping mice is more diverse and more similar to human sleep stages than previously thought. By interrupting the mice's sleep at different moments and then checking how well they remember the learned tasks, the researchers were able to analyze these processes.

When a mouse enters REM sleep, its pupil shrinks, and this is where newly learned tasks - that is, new memories - are reactivated and consolidated, while previous knowledge is not. Conversely, old memories are reactivated and consolidated when the pupil is dilated.

"We are proposing that the brain has this intermediate timescale that separates the new learning from the old knowledge," says professor and study author .

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