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Researchers have discovered a group of neurons in the brain of mice that seem to help sort out “unnecessary memories” during sleep. The study has been published in the journal Science.

As we sleep, the brain processes today’s impressions and sorts them. New events first end up in the part of the brain called the hippocampus. After a while, they are forgotten, or the memories are transferred and stored in the cerebral cortex.

Researchers have now found a group of nerve cells from another part of the brain, the hypothalamus, that sends impulses that help the hippocampus decide which memories should not be saved.

This was seen by the researchers in a variety of advanced tests on mice. There they controlled the activity of these nerve cells in the hypothalamus – and then tested the mice’s memories.

And they saw that the cells were most active during the so-called REM sleep when dreaming, and then some memories were sorted out.

How these cells know which memories to save is still a mystery. Although it is previously known that we remember events to a greater extent linked to strong emotions.

Although the study is done on mice, it may be an important puzzle piece in our understanding of our human brains.


Izawa S, et al. “REM sleep – active MCH neurons are involved in forgetting hippocampus-dependent memories.” Science. 2019. DOI: 10.1126 / science.aax9238.