Scientists Erase a Memory and then Restore it: Implications for Alzheimer's Disease

There may not only be a way to erase a memory, but also to restore it. Scientists have managed to erase a memory in rats before reactivating it, profoundly altering the animals' reactions to past events.

In order to examine the process of memory, the researchers optically stimulated a group of nerves in a rat's brain that had been genetically modified to make them sensitive to light. Then, the researchers simultaneous delivered an electrical shock to the animal's foot. The animals quickly learned to associate the optical nerve stimulation with pain and therefore displayed fear behaviors when these nerves were stimulated. More interestingly, the scientists found that there were chemical changes within the optically stimulated nerve synapses, which showed synaptic strengthening.

After the rats learned this behavior, the researchers then worked on making the rats forget it. They weakened the circuitry by stimulating the same nerves with a memory-erasing, low-frequency train of optical pulses. This caused the rats to no longer respond to the original nerve stimulation with fear.

What was even more fascinating was the fact that the researchers managed to re-activate the lost memory. The researchers re-stimulated the same nerves with a memory-forming, high-frequency train of optical pulses. This re-conditioned the rats once again, which responded to the original stimulation with fear, even though they hadn't had their feet re-shocked.

"We can cause an animal to have fear and then not have fear and then to have fear again by stimulating the nerves at frequencies that strengthen or weaken the synapses," said Sadegh Nabavi, one of the researchers, in a news release.

The findings could actually be used for Alzheimer's research. The beta amyloid peptide that accumulates in the brains of people with the disease weakens synaptic connections in much the same way that low-frequency stimulation erased the memories in rats.

The findings are published in the journal Nature.