Scientists Erase, Restore Rats' Memories, Offering Clues for Alzheimer's
A California team of researchers discovered how to make rats remember and forget.
A whire rat stands on a desk at a medical school in China. California researchers recently found a way to control rats' memories by using fluorescent light.
Scientists Erase, Restore Rats' Memories, Offering Clues for Alzheimer's, PTSD
A California team of researchers discovered how to make rats remember and forget.
California researchers successfully erased and then restored certain memories in rats, a new study declares, offering a potential path for treating Alzheimer’s, post-traumatic stress disorder and other brain ailments.
And they did it all in a literal flash of light.
“It’s very tiny, a fluorescent light that’s shined in, directed precisely at the target that they want it to be aimed at,” says neurologist Chiiko Asanuma, a project officer at the National Institute of Mental Health, which helped fund the study.
The light, fed through a fiber-optic cable, is flashed in different patterns into the rats’ skulls. At lower frequencies – such as once a second – it erased memories; at higher frequencies, it strengthened them.
“It has kind of a science-fiction feel to it,” says Roberto Malinow, a neuroscience professor at the University of California – San Diego, who led the study. “It’s amazing that you can turn a memory off and on at will.”
The light worked not because it affected the brain’s neurons, which are static once they develop, but instead because it influenced the connections between those neurons, known as synapses.
Researchers have long suspected that memories are formed as those synapses grow stronger – and, with illnesses such as Alzheimer’s, erased as those connections become weaker.
That strengthening is called long-term potentiation, or LTP, and as early as the 1970s, scientists knew that if they took a small slice of the brain and then stimulated it at very high frequencies, the synapses would get stronger – in other words, they’d witness LTP.
The challenge, though, was finding a way to carry out LTP inside the skull – and to prove that it would also affect memory.
"It's just a jungle in the brain – too many nerve cells coming through in any one place," Malinow described in a statement.
A powerful tool called optogenetics, though, has offered a new way forward.
Optogenetics are the machinery that allows primitive organisms, such as algae, to be controlled by light from the sun. Malinow surgically implanted optogenetics into the rats’ brains, which in turn made the brains sensitive to light – in this case, blue light. He then inserted a cannula into the rats’ skulls, allowing him to slide a fiber optic cable into their heads and shine blue light onto their brains.
The results only came, though, after some fear conditioning. In conventional conditioning, scientists sound a tone and apply a shock to a rat’s paw. Rats then freeze and act fearfully each time the tone is sounded.
In Malinow’s experiment, he and his team still applied the shock, but instead replaced the tone with the fiber-optic light, which they used in an area of the brain that’s related to auditory fear memory. Just as with conventional conditioning, the rats learned to display fear when the neurons were being stimulated.
Malinow and his team then found they were able to deactivate that conditioning – or that memory of needing to be fearful – through shining the light at lower frequencies, a process known as long-term depression.
Perhaps most remarkably, it could be reactivated just as easily by using the high-frequency pattern of light.
"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," Sadegh Nabavi, a postdoctoral researcher in the Malinow lab and the study's lead author, said in a statement.
The findings have potential implications for people suffering from neurological disorders.
“Alzheimer’s disease weakens synapses in much the same way that we weakened synapses in the study,” Malinow explains.
Hence, the findings suggest that the process may be able to be reversed.
Meanwhile, for those with PTSD, where memories of past horrors seem to be too strong, just the opposite may be true: “Since we were able to remove a memory, potentially similar kinds of manipulations or perturbations or weakening of these kinds of synapses in some way would potentially be able to have beneficial effects in PTSD,” Malinow says.
The findings were published Monday in the journal Nature.
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