Memories are the result of electrochemical changes that take place in brain neurons.
In 2009, following a one-year-long study on sea slugs, which have relatively simple nervous systems, a team led by Kelsey Martin at the University of California were the first to witness memories being made in the form of new proteins appearing at the synapses of brain neurons.
Earlier studies had already shown that memory formation in the brain involves the strengthening of synaptic connections between nerve cells, but actually witnessing the production of new proteins took the science one stage further.
Short-term memories, such as a telephone numbers about to be used, seem to be stored in two small curled-up structures called the hippocampi, buried deep in the brain’s two hemispheres.
Earlier in 2008, researchers at the University of Alabama in Tuscaloosa showed in mice that during the first hour after a memorable event, there were chemical changes to the DNA of neurons in this area, altering the proteins produced.
They also found that there were similar changes to the genes of neurons in the cortex over the subsequent week. They said that these changes seemed to be permanent, indicating that long-term memories are stored in the cortex.
Last year, in 2010, another team led by Sheena Josselyn at the Hospital for Sick Children in Toronto, Canada, found that in mice, they could erase the frightening memory of a noise, by killing amygdala neurons whose synapses had recently been strengthened after exposure to the noise. The amygdala is a brain region that had previously been identified as specifically involved in the creation of fear memories. However, this was the first time a specific memory had been traced to the nerve cells that encoded it.
So, what are memories? It is now known that memories are created by changes in the biochemistry of neuronal synapses and that short and long term memories are associated with different parts of the brain. Short term memories channel through the hippocampus and become longer term memories in the cortex, possibly as part of a sleep process.
The next challenge is how to retrieve memories, and we will post a blog soon on progress in that area of science.