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Researchers reverse head injury amnesia



Memory loss in people who experience repeated head impacts, such as athletes, could potentially be reversed, according to a new study

The study in mice finds that amnesia and poor memory following head injury is due to inadequate reactivation of neurons involved in forming memories.

The research was conducted by researchers at Georgetown University Medical Center in collaboration with Trinity College, Dublin.

Senior investigator, Mark Burns, PhD is a professor and Vice-Chair in Georgetown’s Department of Neuroscience and director of the Laboratory for Brain Injury and Dementia.

He said: “Our research gives us hope that we can design treatments to return the head-impact brain to its normal condition and recover cognitive function in humans that have poor memory caused by repeated head impacts.”

The study showed that the memory loss attributed to head injury was not a permanent pathological event driven by a neurodegenerative disease.

Indeed, the researchers could reverse the amnesia to enable the mice to recall the lost memory, potentially allowing cognitive impairment caused by head impact to be clinically reversed.

The Georgetown researchers had previously found that the brain adapts to repeated head impacts by changing the way the synapses in the brain operate.

This can cause difficulty in forming new memories and remembering existing memories.

In the new study, investigators were able to trigger mice to remember memories that had been forgotten due to head impacts.

The researchers gave two groups of mice a new memory by training them in a test they had never seen before.

One group was exposed to a high frequency of mild head impacts for one week (similar to contact sport exposure in people) and the other group were controls that didn’t receive the impacts.

The impacted rodents were unable to recall the new memory a week later.

Burns said: “Most research in this area has been in human brains with chronic traumatic encephalopathy (CTE), which is a degenerative brain disease found in people with a history of repetitive head impact.

“By contrast, our goal was to understand how the brain changes in response to the low-level head impacts that many young football players regularly experience.”

Researchers have learned that, on average, college American football players receive 21 head impacts per week with defensive ends receiving 41 head impacts per week.

The number of head impacts to rodents in this study were designed to mimic a week of exposure for a college football player, and each single head impact by itself was extraordinarily mild.

Using genetically modified mice enabled the researchers to see the neurons involved in learning new memories, and they found that these memory neurons  were equally present in both the control mice and the experimental mice.

First author, Daniel P. Chapman, Ph.D., said: “We are good at associating memories with places, and that’s because being in a place, or seeing a photo of a place, causes a reactivation of our memory engrams.

“This is why we examined the engram neurons to look for the specific signature of an activated neuron.

“When the mice see the room where they first learned the memory, the control mice are able to activate their memory engram, but the head impact mice were not.

“This is what was causing the amnesia.”

The research team was able to reverse the amnesia to allow the mice to remember the lost memory using lasers to activate the engram cells.

Burns added: “We used an invasive technique to reverse memory loss in our mice, and unfortunately this is not translatable to humans.

“We are currently studying a number of non-invasive techniques to try to communicate to the brain that it is no longer in danger, and to open a window of plasticity that can reset the brain to its former state.”

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