Memory Restoration May Be Possible

By Jane Farrell

Researchers are now able to reactivate a memory that has vanished from the brain.

A study from the University of California, San Diego School of Medicine, detailed how researchers removed a memory from the brain of rat subjects and then restored it. They were able to do this by stimulating nerves in the brain that are already known to weaken and strengthen the connection between the nerve cells that called synapses.

The process altered 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,” said Roberto Malinow, MD, PhD, professor of neurosciences and senior author of the study.

The findings were published in the journal Nature.

The investigators stimulated a group of nerves in the brain had been genetically modified to make them sensitive to light. At the same time, they delivered an electrical shock to the animal’s foot. The rats soon learned to associate the optical nerve stimulation with pain and displayed fear behaviors when these nerves were stimulated.

Analyses showed chemical changes within the optically stimulated nerve synapses, indicative of synaptic strengthening.

The team then weakened this response by stimulating the same nerves with a memory-erasing group of pulses. As a result, the rats no longer responded to the stimulation with fear. That suggested, the researchers said, that the memory of pain had been erased.

Even more startlingly, the researchers were able to eliminate the second memory and restore the first.

“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 the study’s lead author, Sadegh Nabavi, a postdoctoral researcher.

The investigators said their findings could be used in Alzheimer’s research, since that disease weakens synaptic conditions in the same way that the rats’ brains were weakened.