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What do memories look like?

Researchers capture first images of memories being made

BY LÉO CHARBONNEAU | NOV 09 2009

What does a memory look like? A faded photograph? Your child’s face? Neuroscientist Wayne Sossin prefers to leave that sort of metaphysical musing to the philosophers. What interests him are how memories are formed – the actual physical changes that occur in the brain when memory happens.

In the process, he and his colleagues have actually “captured” an image of a memory being made. But don’t get too excited – to the uninitiated it doesn’t look like much more than a few points of glowing green light on a photographic image.

A scientist at the Montreal Neurological Institute, Dr. Sossin says these biomolecular changes are called molecular memory traces. He’s interested in how these memory traces occur, how they differ from each other and what implications that has for memory.

“I think of these different biochemical traces as having different ‘volatility.’ Some of them are easy to remove, some are more difficult to remove. Some last longer and others don’t.”

Psychologists believe short-term memory gets “consolidated” into long-term memory, but Dr. Sossin says, “I think this is really not true.” Long-term memories, he says, are formed through an independent series of mechanisms that differ from how short-term memories are formed. These differences likely affect how stable the memories are.

Dr. Sossin started out in computers – he has a degree in computer science from the Massachusetts Institute of Technology – with an interest in artificial intelligence. But, “I became very disillusioned with that whole field. I really didn’t think it was telling us very much” about intelligence and how the brain works.

The functioning of the brain and the workings of computers are fundamentally different processes, so he turned to molecular biology: “I became enamoured with the techniques of molecular biology to study how memory works.”

The Montreal Neurological Institute, affiliated with McGill University and often referred to simply as “the Neuro,” is recognized internationally for its research in cellular and molecular neuroscience, brain imaging and cognitive neuroscience. It’s quite a remarkable place to work, says Dr. Sossin. “You see these discoveries being made by your colleagues and you can bounce your ideas off of them.”

Recently, Dr. Sossin, with colleagues at McGill and University of California, Los Angeles, scored a coup: using sophisticated imaging techniques, they captured actual images of memories being made. The researchers used nerve cells isolated from the lowly sea slug.

This was the first visual proof, the authors claim, of the mechanism, called protein translation, which underlies long-term memory formation. The study was funded in part by the National Institutes of Health and the Canadian Institutes of Health Research.

The findings, published in Science this past June, show that when a memory is formed, new proteins are made locally at the synapse (the connection between nerve cells), increasing the strength of the synaptic connection and reinforcing the memory.

“The idea that you could actually do that, see the protein being made locally at the synapse and working there, has never been done before,” says Dr. Sossin. “So we’ve demonstrated that this type of molecular trace really does happen.” What’s more, the ability to monitor this process in real time will help researchers to better understand how memories are formed.

“We know the protein synthesis occurs, but why?” asks Dr. Sossin. “What are the steps? If we interrupt these steps, can we block the formation of memory?”

Looked at another way, what is it that determines whether something is going to form a memory or not? And why are some memories fleeting while others last a lifetime? “All of these things, at some level, depend on what the mechanism is,” says Dr. Sossin. “That’s what I want to understand.”

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