-- E.J. Mundell
SUNDAY, June 1, 2014 (HealthDay News) -- Using light to
stimulate key nerve connections in the brains of rats, scientists
were able to erase certain memories, and then restore them with a
second type of light.
"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," study senior researcher Dr. Roberto Malinow, a professor of neurosciences the University of California, San Diego, said in a university press release.
Reporting in the June 1 issue of
Nature, Malinow and his colleagues said they removed and
reactivated memories in rats by stimulating synapses, which are
connections between brain nerve cells (neurons).
To do so, the scientists used light optics to stimulate a bundle
of nerves in the rats' brains that had been genetically tweaked to
make them sensitive to light. At the same time, they delivered an
electric shock to the rodent's foot. In this way, the rats began to
associate the nerve stimulus with the foot pain -- as if they had a
memory of the two occurring together -- and they showed fear
behaviors when the nerves were stimulated, the researchers
The stimulated nerve areas showed chemical changes that
indicated the synapses between the memory-linked brain cells had
gotten stronger after the stimulation.
But the scientists were also able to weaken those memory-cell
connections. They did so by delivering a low-frequency set of light
pulses at the same nerves. In this case, the rodents stopped
responding to the original nerve stimulation -- suggesting that the
pain-association memory had been wiped out.
But what about restoring that lost memory? Malinow's team were
able to do that, too, by re-stimulating the nerve bundle with
another high-frequency pulse of light. In these cases, 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.
"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," lead study author Sadegh Nabavi, a postdoctoral researcher in the Malinow lab, explained in the news release.
Even though animal studies often fail to translate to
applications in humans, the researchers believe there could be
benefits from the research down the line.
One such application might be to help Alzheimer's patients. Beta
amyloid plaques that accumulate in the brains of people with
Alzheimer's disease weaken synaptic connections in much the same
way that low-frequency stimulation erased the rats' memories,
"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," he theorized.
The U.S. National Institute on Aging has more about
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