It has been a common theory among scientists that once a memory is lost, for example in people with amnesia, it’s not possible to retrieve it due to how the part of the brain that holds the memory is too damaged.

Now a series of tests on mice have shown, that when certain nerve cells in the brain are treated and activated with light, using a method called optogenetics, the memories are available once again.

This most likely means that it’s possible to help people with memory loss to get their ability to remember back, even if there would be damages in the parts of the brain where those types of memories are supposedly stored.

Susumu Tonegawa, with the Massachusetts Institute of Technology, talks about the new discovery: “Most researchers have favoured the storage theory, but we have shown in this [study] that this majority theory is probably wrong. Amnesia is a problem of retrieval impairment.”

The new finding strongly indicates that retrograde amnesia, which is caused by for example traumatic injury or the Alzheimer’s disease, does not come from memory storage cell damage, but rather from memory retrieval nerve damage.

Other techniques used for memory recall are memory triggers, which can be a sight or a smell that reminds us of past experiences, and this way of working has been based on the previous suggestion that memories are stored in the brain through long-term physical changes or chemical changes in nerve cells connected to a specific network.

Now, the following research can instead focus on reconnecting the nerve cells in the brain, since this is what the results reveal about how the memories get there in the first place – by nerve cell connections. The study was published in the journal Science, and it gives a new perspective on the treatment of Alzheimer’s or trauma induced memory loss, where strengthening the blocked nerve cell connections could improve memory retrieval in the hippocampus area of the brain.

Image: Robert Cudmore