Scientists discover brain’’s memory ”buffer” in single cells

January 26th, 2009 - 12:04 pm ICT by ANI  

London, January 26 (ANI): A study led by scientists at UT Southwestern Medical Center has revealed that individual nerve cells in the front part of the brain can hold traces of memories on their own for as long as a minute and possibly longer.
This is the first time that a study has identified the specific signal that establishes nonpermanent cellular memory, and revealed how the brain holds temporary information.
Dr. Don Cooper, assistant professor of psychiatry at UT Southwestern and senior author of the study conducted in mice, says that the new finding has implications for addiction, attention disorders and stress-related memory loss.
Permanent memories are known to be stored when the excitatory amino acid glutamate activates ion channels on nerve cells in the brain to reorganize and strengthen the cells” connections with one another.
However, this process takes minutes to hours to turn on and off and is too slow to buffer, or temporarily hold, rapidly incoming information.
The present study has shown that rapid-fire inputs less than a second long initiate a cellular memory process in single cells lasting as long as minute, a process called metabotropic glutamate transmission.
The researchers say that this transmission in the most highly evolved brain region holds moment-to-moment information.
Dr. Cooper says that these cellular findings have implications for how the human brain stores rapidly changing information, like the temporary memory a card shark uses when counting cards in a game of Black Jack and, as casinos have figured out, it is the memory that is most sensitive to the disruptive effects of alcohol and noisy distractions.
“It’’s more like RAM (random access memory) on a computer than memory stored on a disk. The memory on the disk is more permanent and you can go back and access the same information repeatedly. RAM memory is rewritable temporary storage that allows multitasking,” Nature Neuroscience quoted the researcher as saying.
While experimenting on mice, the research team identified a specific metabotropic glutamate receptor (mGluR5) that, when turned on, starts a signalling cascade using calcium to hold a memory trace.
The researchers reveal that this fast, short-term memory process happens inside individual cells. With long-term memory, they add, additional proteins cause slow reorganization between cells in a network to establish a permanent memory.
The researchers examined brain cells from mice using nano-scale electrodes to measure the memory formation process.
They even applied the neurochemical dopamine to the memory buffer nerve cells for understanding how this short-term memory process relates to addiction.
They found that an experimental drug that activates a specific type of dopamine receptor “focused” the nerve cells, making the memory trace less susceptible to distraction.
Upon employing an animal model of drug addiction using cocaine, the researchers found that repeated exposure to addictive levels of cocaine reduced memory trace activation in the memory buffer cells.
When the researchers activated dopamine signalling in the “addicted” animals, essentially adding more dopamine to their systems, no focusing effect was observed.
“This makes sense because we know from human and animal models of addiction, when a decision using working memory has to be made, brain imaging shows a deficit in the same area of the brain we looked at. It all fits together,” Dr. Cooper said.
The team next plan to identify the ion channel responsible for holding and regenerating a memory trace. Their goal is to develop new pharmacological and genetic tools that will help manipulate and possibly expand decision-making memory capacity.
“If we can identify and manipulate the molecular components of memory, we can develop drugs that boost the ability to maintain this memory trace to hopefully allow a person to complete tasks without being distracted,” Dr. Cooper said.
“For the person addicted to drugs, we could strengthen this part of the brain involved with decision-making, allowing them to ignore impulses and weigh negative consequences of their behavior before they abuse drugs,” the researcher added. (ANI)

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