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Experiences shape learning, new research from the University of California, Davis, shows that experience also changes the way neurons become plastic and form new memories. Researchers uses laboratory mice to understand the cellular and molecular mechanisms underlying learning and memory in a brain structure called the hippocampus.
Research with laboratory rodents has shown that a protein- NMDA receptor, found at the connection between nerve cells, is essential for forming new memories. Training mice on a simple task, you can prevent them from learning by giving them a drug that blocks the NMDA receptor. Mice were placed in a novel environment where they had never been before and after a few minutes received a mild foot shock through electrified grids on the floor.
The sensation is about the same as placing tongue on a battery. The shock startled the mice and, as a result, they learned to be scared of the new context. They found that if NMDA receptors were blocked, animals showed no memory for the experience the following day. To see if experienced animals learned the same way, the researchers trained mice who had previously undergone fear conditioning but in a different environment.
When these animals were trained in a new context they could develop a response even when NMDA receptors were blocked. This shows that experienced animals form memories using different plasticity mechanisms than naive subjects even if they are learning about the exact same thing. Neurons form new connections on their prior history- metaplasticity.
Animals form memories by creating and strengthening connections between networks of neurons. Previously activated neurons were more excitable than inactivated ones, they fired many more action potentials when stimulated. Researchers trained experienced mice on the contextual fear conditioning task, they found that GFP cells were preferentially activated, suggesting that they formed the new memory. Instead of using NMDA receptors, these neurons appeared to use a different molecule, the metabotropic glutamate receptor.
Learning new things activates animal’s NMDA receptors which strengthen synapses and forms a new memory network. The activated cells become more excitable, which allows them to encode additional information using a different receptor.