Scientists Confirm Cellular Basis for Memory by Implanting and Erasing Fear in Rats
By controlling the brain cells of rats that had been genetically modified to respond to light, the researchers were able to create memories of terrible events that never took place - and to erase those memories again. Credit: Sadegh Sina Nabavi and Alizadeh
In a recently published study, scientists from the University of California demonstrate the ability to selectively remove and re-predictable memory by stimulating the nerves in the brain at frequencies which are known to weaken and strengthen connections between nerve cells.
Researchers at the University of California, School of Medicine, San Diego have cleared and reactivated memories in rats, profoundly changing the reaction of the animals to past events.
The study, published in the edition of June 1 advanced online edition of Nature, is the first to demonstrate the ability to selectively remove a memory and reactivate predictable by stimulating the nerves in the brain at frequencies that are known to weaken and strengthen the links between nerve cells, synapses.
"We can form a memory, clear the memory and can reactivate at will by applying a stimulus that strengthens or weakens the selective synaptic connections," said Roberto Malinow, MD, PhD, professor of neuroscience and lead author of the study.
Scientists optically stimulated a group of nerves in the brain of a rat that had been genetically modified to be sensitive to light, and at the same time gives an electric shock to the foot of the animal. The rats quickly learned to associate the stimulation of the optic nerve with pain and fear behaviors displayed when these nerves are stimulated.
Analyses showed signs of chemical changes in nerve synapses optically stimulated synaptic strengthening.
In the next step of the experiment, the research team has demonstrated the ability to reduce the circuit by stimulating the same nerve with a memory erase, low burst optical frequency. These rats respond more responded to stimulation of the original nerve with fear, suggesting the association of pain memory had been erased.
In what might be the most surprising finding of the study, scientists found that they could revive the lost re-stimulate the same nerves with a train of optical pulses in memory of memory training high frequency. These rats repaired once again responded to the stimulus of the original fear, even if they had not had their feet re-shock.
"We can not force an animal to fear and then do not be afraid and fear again by stimulating nerves at frequencies that strengthen or weaken synapses," said Sadeq Nabavi, a postdoctoral researcher in the laboratory Malinow and lead author of the study .
As for potential clinical applications, Malinow, which occupies the Shiley Chair in research on Alzheimer's disease in honor of Dr. Leon Thal, said the beta amyloid peptide that accumulates in the brains of people with the disease Alzheimer weakens the synaptic connections in the same way that the low frequency stimulation in rats erase memories. "Since our work shows that we can reverse the processes that weaken synapses, which could offset some of the effects of beta-amyloid protein in patients with Alzheimer's disease," he said.
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