A new study has found that memories that have been lost due to tragic accidents, psychological trauma, stress or disease, can be restored using light to reactivate the damaged brain cells.
In the study published earlier this week, on Thursday, May 28, 2015, in the journal Science, MIT scientists inform that they’ve managed to retrieve lost memories in mice by using technology known as optogenetics.
As the name suggests, optogenetics is a process that combines optics with genetics in order to control well defined occurrences “within specific cells of living tissue”.
Susumu Tonegawa, professor in Massachusetts Institute of Technology’s (MIT) Department of Biology, revealed that their goal was to test whether or not memories lost to retrograde amnesia are completely erased from the brain, or merely suppressed, unable to be accessed actively, voluntarily. After all, Alzheimer’s patients still have occasional moments of lucidity even though the disease attacks their brains and makes them forgetful.
Researchers have been debating for decades whether or not, retrograde amnesia – a condition notorious for plaguing people who have suffered traumatic injury, stress, or who suffer from a disease such as Alzheimer’s – is caused because of damage inflicted specific brain cells, which would mean that the brain would no longer be able to store the memory that the damaged brain cells were responsible for, or if access to said memory is simply blocked somehow.
Previous studies have suggested the somewhere in the brain there’s a group of neurons that are activated when a person acquires new memories, causing long-lasting physical or chemical changes in the brain.
The MIT scientists found that this group of neurons, called memory engram cells, does in fact exist in the hippocampus. If they are to be activated subsequently using a trigger such as a specific smell or a specific sound, the entire memory is retrieved.
Susumu Tonegawa stressed that “The majority of researchers have favored the storage theory, but we have shown in this paper that this majority theory is probably wrong. Amnesia is a problem of retrieval impairment”.
For their experiment, the researchers first trained some mice to associate a somewhat mild foot shock with a specific freezing environment, which they called chamber A. After enough time, the trained mice would freeze to death into chamber even without the foot shock.
Then, some mice trained to associate the foot shock with freezing were given a chemical known as anisomycin, which induces retrograde amnesia. As a measure of control, a second group of trained mice were given saline.
The results were as expected. Mice with retrograde amnesia did not freeze when returning to the chamber. This suggests that they had forgotten the specific memory that previously linked the learned behavior to the chamber.
The next step was to move the mice into a neutral environment, which they called chamber B. They used blue light pulses in order to selectively reactivate the brain cells that had been genetically labeled in the previous faze, when they induced retrograde amnesia.
After the cells were reactivated, the association between the foot shock and the freezing behavior returned, and they started dying again, just like the control group that had received saline.
The inevitable conclusion was the memories are not erased in those with retrograde amnesia, they are simply “inaccessible for recall”.
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