Dan Campbell felt the bullets whiz past his head. The tracer rounds zipped between his legs. It was his first firefight as a Canadian soldier in Afghanistan.
"I was completely frightened and scared like I'd never been before in my life," he says.
As the attack continued, the sights, sounds and smells started to form memories inside his brain. The fear he felt released the hormone norepinephrine, and in the complex chemistry of the brain, the memories of the battle became associated with the fear.
'I think one day, hopefully in the not-too-distant future, we will be able to delete a memory.'- Dr. Sheena Josselyn, senior scientist, Hospital For Sick Children Research Institute
Six years later, a sight or sound such as a firecracker or car backfiring can remind him of that night in 2008. The fear comes back and he relives rather than remembers the moments.
"It can be hard. Physically, you know, there's the tapping foot, my heart beating," he says.
Like so many soldiers and victims of assault or people who have experienced horrific accidents, Campbell was diagnosed with post traumatic stress disorder.
Now a newspaper reporter in Yellowknife, Campbell thinks one day he may get therapy. But for now he is working on his own to control the fear and anger the memories bring.
But what if he could just erase those memories? What if he could wipe out the fear as if it never existed?
Some memory researchers believe they are getting closer to helping former soldiers like Campbell and others haunted by the past delete the fear memories.
Warning system
Memory, in an evolutionary sense, is about survival, says Dr. Sheena Josselyn, a senior scientist at the Hospital For Sick Children Research Institute in Toronto.
It is our warning system to prevent us from repeating dangerous actions.
But traumatic memories, such as those in the brains of people with PTSD, can interfere with daily living. They can cause sleeplessness, or if sleep comes, disturbing dreams. They can bring moments of anxiety and can make normal relationships with others impossible.
In her lab, Josselyn is working to find a way to delete, or at least dampen, the fear associated with traumatic memory.
Current research says a memory is located in various parts of the brain. The neurons, or brain cells, that are encoded with the fear are in one part of the brain while other parts of the memory are elsewhere.
Josselyn, working with rodents in the lab, is developing ways of locating the group of neurons that hold the fear. Once she has that, then she hopes to target just those cells chemically and disrupt their ability to keep that fear encoded.
"We're not there yet," she says, but "we're certainly getting close in rodents."
"I think one day, hopefully in the not-too-distant future, we will be able to delete a memory."
Ethical hurdle
There are many hurdles to overcome. The brain has 86 billion neurons. The memories Josselyn is working with may be stored in as few as several hundred neurons.
Scientists are researching ways of deleting traumatic memories in the human brain, such as those created in the midst of war. (Kirsty Wigglesworth/AP)
Current techniques are nowhere near specific enough to delete so small a group and leave everything else intact.
And there is an ethical hurdle. Some ethicists believe that deleting memories deletes a vital part of a person's identity.
"It's those emotions that tell you who I am," says Dr. Francoise Baylis, who holds the Canada Research Chair in bioethics and philosophy at Dalhousie University in Halifax.
Baylis cautions that deleting even the worst of a person's memories can interfere with the sense of self.
She does not want people to suffer, but she says learning how to deal with the fear and anxiety can produce strength.
'Anything but a disorder'
Campbell questions the research as well. He believes his memories, his fears and anxiety are part of who he is.
"You go to a place and see some pretty horrible stuff and you're a little different after, sometimes [you have] strange mental reactions. I think that is anything but a disorder. That's normal."
Back in her lab, Josselyn knows that her research may not be for everyone.
But for those who cannot function because of traumatic memories, she wants to relieve the suffering. She suggests that what she is proposing could produce the same effect as therapy, but faster.
"Some people would argue, and I wouldn't disagree, that what cognitive therapy does is eventually change your brain's circuits," she says.
"So we are doing the same thing that cognitive therapy might do. They are taking away the emotional component of a memory in much the same way we do. It's always towards the common goal, it's just the routes in are different."
Dick Miller's documentary Hit Delete airs on CBC Radio's Ideas program on Sept. 24 at 9pm ET.
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