In first of its kind of study, the researchers have successfully stimulated key nerve connections in the brains of rats using light. This has allowed them to erase certain memories and then restore them with a second type of light.
Lead researcher Dr. Roberto Malinow of the University of California-San Diego, said, “The study is the first to show evidence that strengthened connections between neurons in the brain are involved in memory.”
“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,” he said.
The researchers removed and reactivated memories in rats by stimulating synapses, which are connections between brain nerve cells (neurons).
For the experiment, the scientists used light optics to stimulate a bundle of nerves in the brains of genetically tweaked rats. At the same time, the researchers delivered an electric shock to the rodent’s foot. This made the rats associate the nerve stimulus with the foot pain.
The stimulated nerve areas showed chemical changes that indicated the synapses between the memory-linked brain cells had gotten stronger after the stimulation. Soon after, the scientists weakened those memory-cell connections.
The best part of the research was that, they were able to restore the lost memory. The researchers re-stimulated the nerve bundle with another high-frequency pulse of light. During the process, the rats responded to the stimulation with fear even though their feet were not being shocked. According to the scientists, that suggests that they had “restored” the fear-linked memory.
Study author Sadegh Nabavi, a postdoctoral researcher in the Malinow lab, said, “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.”
The researchers believe there could be huge benefits of the findings in treating memory related issues like Alzheimer’s.
National Institute of Mental Health (NIMH) Director Dr. Thomas R. Insel said, “Beyond potential applications in disorders of memory deficiency, such as dementia, this improved understanding of how memory works may hold clues to taking control of runaway emotional memories in mental illnesses, such as post-traumatic stress disorder.”
The findings of the study are published in the journal Nature. The study was funded by the NIMH.