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A group of researchers has shed new light on the workings of Amnesia. The study conducted on mice, was carried out by a team of researchers, and scientists from the reputed RIKEN-MIT Center for Neural Circuit Genetics (CNCG). The institute is located in Saitama, Japan. The findings which were published on May 28, in the U.S. journal named Science, indicate that the researchers found hints that past memories do exist in the brain of the mice which is affected by amnesia. However, they are simply too weak to be recalled. They further demonstrated that old memories can be reactivated using blue light pulses on the hidden cellular pathways, thereby helping in strengthening them a great deal.
Neuroscientists have actively debated retrograde amnesia, or memory loss after brain trauma, and whether they are entirely non-existent or if they are just incapable of being recollected. In human beings, amnesia is linked to Alzheimer’s disease, traumatic brain injury, and other neurological conditions. Susumu Tonegawa, Director, RIKEN Brain Science Institute (RIKEN BSI), guided the team of researchers which was curious to know more about the process of the formation of memories in the brain. Additionally, the question on their minds was if by chemically stimulating the occurrence of retrograde amnesia, memories could be disrupted, and then at a later point of time, still be recalled.
Tonegawa, along with lead authors Michelle Pignatelli, Dheeraj Roy, and Tomas Ryan, reported using an engineered virus along with blue light pulses to stimulate the neurons that get triggered as memories are created. These are also known as memory engrams. The technology called ‘optogenetics’, was used to reactivate memories that are suppressed or otherwise cannot be retrieved. This suggests that retrograde amnesia is more a problem of retrieving a memory, rather than an actual loss of information.
The study involved mice being kept in a particular enclosure, and creating a bad memory by repeatedly shocking the mice. Scientists tracked the neurons that were stimulated when the mice experienced the fear of the shock container. In a new batch of mice, the scientists made those memory engrams sensitive to light, before studying them with the same shock treatment. In this way, the group of researchers has shed new light on the workings of Amnesia.
In the wake of the initial findings, some mice were injected with anisomycin, a drug used to make memories disappear the way they might in someone with retrograde amnesia. Those mice displayed no fear while in the shock chamber, until analysts used the blue light to stimulate the neurons they knew contained the repressed memory, causing their fear to return. Eventually, the study helped scientists in discovering that the engram cells were powerfully connected from one part of the hippocampus region of the brain to another part of the hippocampus. There are two hippocampi regions in the brain of humans and other mammals, one on each side. It is a part of the limbic system, and plays a crucial role in forming, storing, and transferring information from short-term memory to long-term memory.
The scientists examined the region closely, and evaluated that it was a design that had withstood the drug treatment. They further concluded that other sections of the brain where memories of fear can be found, including the amygdala, were also affected in this structure. The team was therefore able to recover the memories because different connections in the brain, such as the ones unaffected by the drug, but not accessible without the light treatment, were also collecting information associated to the shock treatment. The finding published by the team of researchers has shed new light on the workings of Amnesia, and has the potential to improve the living conditions of people who suffer from Alzheimer’s disease or any kind of trauma.
By Ankur Sinha
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