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Journalism of Courage
Researchers have found clues on a long-standing mystery — how the brain avoids overwriting old memories when new ones are created.
They have found that in mice, the brain processes new and old memories in separate phases of sleep, which might be helping in separating new and old memories.
The study, ‘Sleep microstructure organises memory replay’ was published in the journal Nature last week. It was carried out by scientists based at Cornell University in the United States.
For their analysis, the researchers, over the course of a month, taught a variety of tasks to a group of mice. They then equipped the mice with brain electrodes and tiny spy cameras that hung in front of their eyes to track their pupil dynamics when they went to sleep.
“One day, the mice learned a new task and when they fell asleep, the electrodes captured their neural activity and the cameras recorded the changes to their pupils,” according to a press statement.
The researchers interrupted the mice’s sleep at different moments and subsequently, tested how well they recalled their learned tasks.
It was found that new memories are repeated and consolidated when the pupil is smaller during a sub-stage of non-REM sleep — the stage of sleep most associated with memory consolidation. Old memories are repeated when the pupil is larger.
Azahara Oliva, co-author of the study and a physicist at Cornell University, told Nature, “The brain was preserving the older memories during this large-pupil sub-state, but incorporating new memories during the small-pupil sub-state,”. This two-phase system is a “possible solution to this problem of how the brain can incorporate new knowledge but also maintain the old knowledge intact”.
