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Past Winner
2009 E.W.R. Steacie Memorial Fellowship

Karim Nader


McGill University

Karim Nader
Karim Nader

Karim Nader knows the fear response as well as anyone. Whether in mice or men, our bodies freeze, pupils dilate, the heart-rate spikes. And we remember. There's nothing stronger than fear for fixing a memory in our minds.

Seven years ago, the now 40-year-old McGill University associate professor of psychology experienced a professional version of the fear factor. As a postdoctoral student, he published his first scientific paper on memory. The results showed that it was possible to chemically erase fearful memories in rats. But more importantly, in terms of the neurobiology of memory, the results revealed that long-term memories can be unlocked — and changed. This challenged a century of thinking about the neural basis for memory.

“The results created a scientific shock wave. At one conference I had a senior researcher come up to me and say ‘Your data is very strong, but I just can't believe it. I just can't believe that's the way it works,’” says Dr. Nader, recipient of a 2009 NSERC E.W.R. Steacie Memorial Fellowship.

But after a decade of defending and explaining his research — and confirmation of the results by lab groups around the world — Dr. Nader's research isn't engendering fear, but hope.

His research is deepening our understanding of the molecular basis by which memories are created, changed and destroyed. And it's offering relief for those suffering from psychological disorders that involve uncontrollable, intrusive memories, most notably Post-Traumatic Stress Disorder (PTSD).

What many memory researchers couldn't believe is that when we recall memories, we chemically unwire them. In the 20th century, the canonical belief among psychologists was that long-term memories are chemically hard-wired, a process called cellular consolidation.

Nader's rat experiments revealed that when memories are recalled they are chemically unlocked (for example, when we verbally recount a past experience). These memories must thus be chemically reconsolidated. And in the process of reconsolidation, it's possible to change our sense of the past.

“During this period of reconsolidation, it's possible to chemically or behaviourally erase or change a memory,” says Dr. Nader. “Memories aren't just snapshots of things that get stored away in some drawer and never change. Every time you recall a memory you're changing it slightly. What we've discovered is a mechanism that can explain some of the changing nature of a memory.”

Ironically, Dr. Nader's research resurrected 40-year-old findings by American psychologist Donald Lewis Misonin, results that had been rejected and largely forgotten. Now memory reconsolidation has been shown in animals from fruit flies and sea slugs, to chickens and humans.

All the more remarkable, Dr. Nader's research has already produced clinical benefits. Nader and colleagues, including McGill University clinical psychologist Alain Brunet, have demonstrated that interrupted reconsolidation can be used to relieve the suffering of patients with chronic PTSD. The therapy involves administering a common blood pressure drug, propranolol, as a traumatic event is recounted. The propranolol partially blocks the reconsolidation of the fear associated with the memory.

“The goal isn't to completely erase the memory,” says Dr. Nader. “We just want to turn down the intensity of the emotional component of the memory so that it's not overwhelming, and can then be treated with traditional forms of therapy.”

Since his initial findings, Dr. Nader has pursued a more specific understanding of the molecular basis of locking and unlocking memories.

“Until recently, no one had figured out how to test the neurobiology that shifts a memory from a locked state to an unlocked one,” he says.

His McGill lab group demonstrated that if a specific chemical pathways in neurons — the NMDA receptors — are chemically blocked, a memory cannot be unlocked.

As part of his Steacie research Dr. Nader will tease out another component of the memory mystery: the behavioural and chemical basis for whether fear memories are intertwined.

“We're trying to see what parameters cause the brain to store memories together, or separately. At present, there's no neurological data on this,” says Dr. Nader. “Clinically it's important to understand whether memories are stored as one or separately. This will enable us to predict if, when treating a particular traumatic memory, other related memories could be impaired.”