How Our Brains Make Two Copies of the Same Memory

One thing I love about studying neuroscience is that it is constantly changing, upending long-held views with more sophisticated research.  This particular discovery, published earlier this month, overturned a neuroscience tenet of some 50 years – here’s the story as reported by the PBS Nova site:

For decades, we’ve thought that memories were formed in two distinct stages—short-term first, then long-term later.

We might be wrong.

New research suggests that our brains make two copies of each memory in the moment they are formed. One is filed away in the hippocampus, the center of short-term memories, while the other is stored in cortex, where our long-term memories reside.

These findings were published April 6 in the journal Science.

The historically well-known patient Henry Molaison, also known as H.M., helped solidify the prevailing theory of memory formation and storage during the mid-1950’s. After a brain surgery to treat his epilepsy damaged his hippocampus, he could no longer form new memories. But those memories he made before his surgery still existed, leading neuroscientists to believe that the hippocampus was key to forming new memories.

And in the new theory, it still is. Though the research suggests that the link between the hippocampus and the cortex is as linear as once thought. When the link is blocked, the mice in the experiment didn’t develop long-term memories, just like H.M.

But when the connection is present, memories form in both the cortex and the hippocampussimultaneously. For the first few days, though, the neurons in the hippocampus are the only ones that fire during memory retrieval. Eventually, the memories in the cortex mature, and the neurons involved light up when the memory is recalled.

The researchers, based at the Riken-MIT Center for Neural Circuit Genetics in Japan, used a relatively new technique known as optogenetics to both trace memory formation and test the roles of the hippocampus and cortex. Optogenetics involves genetically engineering animals—in this case mice—to express a light-sensitive protein in certain neurons. By implanting fine fiber-optic cables into their brains, researchers are effectively able to turn specific neurons on and off, which allows them to probe their function.

Here’s a link to the full story: