"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, a post-doctoral researcher and the study's lead author."
Washington, June 2 - Imagine this - removing a bad memory or reactivating a good memory may be done at flick of the finger or the click of a mouse.
In promising results, researchers have erased and reactivated memories in genetically-engineered rats - profoundly altering the animals' reaction to past events.
We can form a memory, erase that memory and we can reactivate it, at will, by applying a stimulus that selectively strengthens or weakens synaptic connections, explained Roberto Malinow, a professor of neurosciences at University of California, San Diego's school of medicine.
In lab settings, scientists optically stimulated a group of nerves in a rat's brain that had been genetically modified to make them sensitive to light, and simultaneously delivered an electrical shock to the animal's foot.
The rats soon learned to associate the optical nerve stimulation with pain and displayed fear behaviours when these nerves were stimulated.
In the next stage, the team demonstrated the ability to weaken this circuitry by stimulating the same nerves with a memory-erasing, low-frequency train of optical pulses.
These rats subsequently no longer responded to the original nerve stimulation with fear, suggesting the pain-association memory had been erased.
Scientists found they could re-activate the lost memory by re-stimulating the same nerves with a memory-forming, high-frequency train of optical pulses.
These re-conditioned rats once again responded to the original stimulation with fear, even though they had not 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, a post-doctoral researcher and the study's lead author.
The discovery is a good news for people with Alzheimer's disease, researchers noted in a paper published in the journal Nature.