Neuroscientists say it's possible to overwrite bad memories
Tokyo (AFP) - Emotions connected
to memories can be rewritten, making bad events in the past seem better
and good things appear worse, scientists from Japan and the United
States have found.
The discovery
of the mechanism behind the process helps to explain the power of
current psychotherapeutic treatments for mental illnesses such as
depression or Post Traumatic Stress Disorder (PTSD), they said, and
could offer new avenues for psychiatric help.
"These
findings validate the success of current psychotherapy, by revealing
its underlying mechanism," research leader Susumu Tonegawa told AFP in
Tokyo.
The team, formed from
a collaboration between Japan's RIKEN institute and the Massachusetts
Institute of Technology in the US, used optogenetics -- a new
brain-control technology which utilises light -- to better understand
what happens when we reminisce.
They
found that warm feelings or intense fear triggered by the interaction
between the hippocampus -- the brain's diary room -- and the amygdala --
the place believed to encode positivity or negativity -- are more
flexible than previously thought.
"It depends on how strongly the
(good or bad aspect) dominates... there is competition between the two
circuits' connection strengths," Tonegawa said.The researchers injected two groups of male mice with light-sensitive algae protein.
This allowed them to identify the formation of a new memory as it was happening and then use pulses of light to reactivate it when they wanted to.
One group of rodents were
allowed to play with female mice, creating a positive memory. The other
group were given a small but unpleasant electric shock through the
floor.
- Painful memory -Researchers then artificially reactivated the memory using the light pulses -- effectively making the mice remember what had happened to them.
While
the mice were "remembering" their event, they were given the opposite
experience -- the mice with the nice memory got a shock, while those
with the painful memory were introduced to females.
Tonegawa
said his team had discovered that the emotion of the new experience
overpowered the original emotion, rewriting how the mice felt about it.
"We did a test in the original chamber and the original fear memory was gone," he said.
However,
the over-writing of a memory was only possible by manipulating the
hippocampus, which is sensitive to context. The same result could not be
achieved by manipulating the amygdala.
Tonegawa
said the connection between the contextual memory in the hippocampus
and the "good" or "bad" emotions in the amygdala became stronger or
weaker depending on what was experienced.
The
researchers hope their findings might open up new possibilities for
treatment of mood-affecting disorders such as depression, or PTSD, a
condition found in people such as soldiers who have undergone
life-threatening or particularly horrific events.
"In
the future, I would like to think that with new technology we will be
able to wirelessly control neurons in the brain, without intrusive tools
like electrodes," said Tonegawa, who won the Nobel Prize for Physiology
and Medicine in 1987.
"We could possibly augment good memories over bad ones," he said.The research paper is published in Nature.
In a commentary, also carried by Nature, cognitive researchers Tomonori Takeuchi and Richard Morris at the University of Edinburgh in Scotland said the study broke new ground in exploring the mechanisms of memory, although optogenetics had limitations as a tool for doing this.
"Molecular
engineering is nonetheless shedding light on our understanding of the
underlying physiological networks of memory," they wrote.
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