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A type of brain cell called astrocytes play a crucial role in stabilizing memories in the brain.Credit: Jose Calvo\/SPL<\/p>\n
Why are we able to remember emotional events so well? According to a study published today in Nature1<\/a>, a type of cell in the brain called an astrocyte<\/a> is a key player in stabilizing memories for long-term recall.<\/p>\n Astrocytes were thought to simply support neurons<\/a> in creating the physical traces of memories in the brain, but the study found that they have a much more active role \u2014 and can even be directly triggered by repeated emotional experiences. The researchers behind the finding suggest that the cells could be a fresh target for treating memory conditions such as those associated with post-traumatic stress disorder and Alzheimer\u2019s disease. <\/b><\/p>\n \u201cWe provide an answer to the question of how a specific memory is stored for the long term,\u201d says study co-author Jun Nagai, a neuroscientist at RIKEN Center for Brain Science in Wako, Japan. By studying astrocytes, Nagai said, the study identifies how the brain selectively filters important memories at the cellular level.<\/p>\n Stable memories<\/p>\n Nagai and his colleagues focused on the question of memory stabilization: how a short-term memory becomes more permanent in the brain. Previous research had found physical traces of memories in neuronal networks in brain regions such as the hippocampus and amygdala2<\/a>. But it was unclear how these \u2018engrams\u2019 were stored in the brain as lasting memories after repeated exposure to the same stimulus.<\/p>\n To dig deeper, the researchers developed a method for measuring activation patterns in astrocytes<\/a> across a whole brain of a mouse as it completes a memory task. They measured the upregulation of a gene called Fos \u2014 an early marker of cell activity that is associated with the physical traces of memories in the brain3<\/a>.<\/p>\n In a well-established fear-conditioning memory task, mice learnt to associate a certain cage with unpleasant shocks to their feet while the researchers tracked the level of Fos in their brains. Days later, the animals would re-enter the cage and recall the unpleasant sensation. The researchers observed strong Fos upregulation in astrocytes in the animals\u2019 amygdalas and other brain regions when mice re-entered the cage, but not during the initial learning phase, suggesting that astrocyte activity was more important for recalling past events than creating new memories.<\/p>\n \u201cThe surprise was that astrocytes did not respond to the fear experience the first time, only the second time,\u201d says Nagai.<\/p>\n
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