In a study right out of sci-fi, researchers at The University of California, San Diego School of Medicine erased and restored memories in rats.

The study, published in the journal Nature, is the first of its kind to prove that strengthening and weakening the relationships between neurons in the brain, called synapses, can hugely affect memory recall.

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,” said senior author Roberto Malinow, MD, PhD, professor in the Department of Neurosciences and neurobiology section of the Division of Biological Sciences, in a university press release.

During its study, the team of researchers applied optical lasers as the stimulus to the brains of rats that had been genetically engineered to be sensitive to light. Simultaneously, they delivered an electrical shock to each rat’s foot. Soon the rats made the connection between the two and showed signs of fear when their optic nerves were stimulated, even without the shock. Analyses of the experiment showed chemical changes within the stimulated nerve synapses, which was indicative of synaptic strengthening.

The researchers then stimulated the neurons with a different, low-frequency sequence of optical pulses in order to weaken the connections. The rats stopped responding to the nerve stimulation with fear, meaning that the pain-association memory had essentially been erased.

The most interesting, and perhaps most useful, part of the research came in the next step—when scientists reactivated those same lost memories. By stimulating the same neurons with high-frequency pulses, researchers were able to reinstate those same lost memories, without any extra shocks.

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 postdoctoral researcher in the Malinow lab and the study’s lead author.

The findings are exciting for what they could mean for the potential of Alzheimer’s health. Malinow, who holds the Shiley Endowed Chair in Alzheimer’s Disease Research in Honor of Dr. Leon Thal, pointed out that the beta amyloid peptide that accumulates in the brains of Alzheimer’s disease patients weakens synaptic connections in much the same way that the low-frequency stimulation erased memories in the rats. This could mean that with more research, restoring memories in those who are most affected by memory loss could be in the near future.

“Since our work shows we can reverse the processes that weaken synapses, we could potentially counteract some of the beta amyloid’s effects in Alzheimer’s patients,” Malinow said.
The research was funded, in part, by the National Institutes of Health and Cure Alzheimer’s Fund.