Kerri Smith
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A single, specific memory has been wiped from the brains of rats, leaving other recollections intact.
The
study adds to our understanding of how memories are made and altered in
the brain, and could help to relieve sufferers of post-traumatic stress
disorder (PTSD) of the fearful memories that disrupt their lives. The
results are published in Nature Neuroscience1.
The
brain secures memories by transferring them from short-term to
long-term storage, through a process called reconsolidation. It has
been shown before that this process can be interrupted with drugs. But
Joseph LeDoux of the Center for Neural Science at New York University
and his colleagues wanted to know how specific this interference was:
could the transfer of one specific memory be meddled with without
affecting others?
"Our concern was: would you do something really massive to their memory network?" says LeDoux.
Scary music
To
find out, they trained rats to fear two different musical tones, by
playing them at the same time as giving the rats an electric shock.
Then, they gave half the rats a drug known to cause limited amnesia
(U0126, which is not approved for use in people), and reminded all the
animals, half of which were still under the influence of the drug, of
one of their fearful memories by replaying just one of the tones.
When
they tested the rats with both tones a day later, untreated animals
were still fearful of both sounds, as if they expected a shock. But
those treated with the drug were no longer afraid of the tone they had
been reminded of under treatment. The process of re-arousing the rats'
memory of being shocked with the one tone while they were drugged had
wiped out that memory completely, while leaving their memory of the
second tone intact.
LeDoux's team also confirms the idea that a part of the brain called
the amygdala is central to this process - communication between neurons
in this part of the brain usually increases when a fearful memory
forms, but it decreases in the treated rats. This shows that the
fearful memory is actually deleted, rather than simply breaking the
link between the memory and a fearful response.
Greg
Quirk, a neurophysiologist from the Ponce School of Medicine in Puerto
Rico, thinks that psychiatrists working to treat patients with
conditions such as PTSD will be encouraged by the step forward. "These
drugs would be adjuncts to therapy," he says. "This is the future of
psychiatry - neuroscience will provide tools to help it become more
effective."
http://www.nature.com/news/2007/070305/full/070305-17.html
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