Ask Doctor K: Memories lost may be recoverable

DEAR DOCTOR K: When we lose memories, do we lose them forever?

DEAR READER: Specific memories are thought to reside inside a small group of nerve cells that “talk” to each other.

Each nerve cell has little projections that, microscopically, look like trees with branches and twigs. The branches and twigs of one nerve cell send chemical signals that reach the branches and twigs of another nerve cell. That’s how nerve cells talk to each other.

We used to think that when a person lost a memory, it probably reflected irreversible damage to the synapses involved in that memory. When a patient with Alzheimer’s disease forgets the name of his son, we assumed the connections between the nerve cells that store that name have been damaged beyond repair.

On reflection, there was a good reason to have questioned that assumption. Anyone who has known people with Alzheimer’s disease knows that, at least early on, memories are fitful. A patient may forget his son’s name one day and remember it the next.

Some remarkable studies from the laboratory of Dr. Susumu Tonegawa, a Nobel Prize-winning scientist at MIT, indicate that memory loss may not be permanent.

Tonegawa’s team studied normal mice and mice with a form of Alzheimer’s disease. The mice were placed in a cage that delivered an unpleasant electric shock to their feet. A few hours later, the mice were placed back in the cage: They all froze in fear.

However, days later the mice were placed back in the same cage. The normal mice were fearful. In contrast, the mice with Alzheimer’s-like disease weren’t frightened.

The scientists located where in the brains of the mice the memory of the shock was stored. They used optogenetics to stimulate that area in the mice with Alzheimer’s-like disease. This time, those mice froze in fear when they were placed in the cage.

The research offers hope scientists will be able to figure out how to retrieve memories.

Don’t hold your breath; that day is a long way off. But if and when it comes, it will be an important milestone.