Scientists find secret of reversing bad memories

Thursday 28 August 2014

Scientists find secret of reversing bad memories

Bad memories could be reversed after scientists discovered the part of the brain which links emotions to past events

Scientists at MIT have discovered which part of the brain controls bad memories and how to reverse them

By  Sarah Knapton, Science Correspondent

6:00PM BST 27 Aug 2014

Bad memories of past trauma can leave people emotionally scarred for life.

But now neuroscientists believe they can erase feelings of fear or anxiety attached to stressful events, in a breakthrough which could help treat depression or post-traumatic stress disorder.

Researchers at MIT, US, have discovered which brain circuits attach emotions to memories, and crucially, how to reverse the link.

They managed to ‘switch off’ feelings of fear in mice which had been conditioned to feel anxious. It is likely the same technique could be used in humans.

“In our day to day lives we encounter a variety of events and episodes that give positive or negative impact to our emotions,” said Susuma Tonegawa, Professor of Biology and Neuroscience at the Riken-MIT Centre for Neural Circuit Genetics.

“If you are mugged late at night in a dark alley you are terrified and have a strong fear memory and never want to go back to that alley.

“On the other hand if you have a great vacation, say on a Caribbean island, you also remember it for your lifetime and repeatedly recall that memory to enjoy the experience.

“So emotions are intimately associated with memory of past events. And yet the emotional value of the memory is malleable. Recalling a memory is not like playing a tape recorder. Rather it is like a creative process.

“The circuits seem to be very similar between human and mice when it comes to memory formations and the emotions of memories. So a similar technology could be available for humans.”

Memories are made of many elements, which are stored in different parts of the brain. The context of a memory, such as the location and time that the event took place, is stored in cells in the hippocampus, while emotions linked to that memory are found in the amygdala.

The team studied which brain cells were active when mice were experiencing a pleasant experience – a male mouse socialising with a female mouse – or a negative experience – a mild electrical shock.

They then showed that by stimulating the neurons associated with the opposite emotion they could reverse the feeling attached to the memory. Mice became more relaxed in situations where they had previously been anxious and more fearful where they had previously been content.

“We found that we can dictate the overall emotion and the direction of the memory.” added Prof Tonegawa, “We could switch the mouse’s memory from positive to negative and negative to positive.”

The brain cells are triggered by a technique called optogentics which uses pulses of blue light to trigger the neurons into firing.

Previous studies have shown that memories can change over time as recollections become more vague or events that never happened are remembered. Behavioural therapists often take patients back to a traumatic event and ‘rewire’ their

But this is the first time that scientists have shown which brain circuits are responsible for positive and negative emotions, and reversed them.

Professor Richard Morris at the Centre for Cognitive and Neural Systems at the University of Edinburgh said: “We often believe that our memories are accurate, but in fact they are malleable.

“The memory of a romantic first date with a partner may take on a different mood when the relationship falters. That of a favourite family beach in summer may be destroyed after witnessing a swimming tragedy

“Molecular engineering is shedding light on our understanding of the underlying physiological networks of memory.”

The researchers are hopeful it could lead to a cure for depression or post-traumatic stress disorder without the need for medication.

“It’s not something we can do next week, but we are now developing a variety of methods to try to target the stimulation of the human brain cells,” added Prof Tonegawa.

“Instead of going inside the brain you stimulate from the surface of the brain which would be less invasive.

“I want to make it clear that we have not used this technology in order to alter normal healthy people’s mind or cognition. That we should not do. If there is any application in human it would be for pathological conditions.”

The research was published in the journal Nature.


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