Shades of 'Eternal Sunshine of the Spotless Mind' as neuroscientists
rub out particular memories in rats
<http://www.nature.com/news/2007/070305/full/070305-17.html>

Wipe out a single memory

Drug can clear away one fearful memory while leaving another intact.
Kerri Smith - Published online: 11 March 2007

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>