Can we restore memories we’ve lost?

Ask the doctor

Q. How do we store memories in our brain, and is there hope that someday we might be able to restore memories we've lost?

A. We remember just a tiny fraction of the events of our lives. The sights and sounds of every conscious moment could become a memory. But only when a moment seems important do we remember it, at least for a while. I remember the radiant beauty of my wife's face on our wedding day, at the moment she lifted the veil.

You ask what is happening when we store away a memory, and when we remember it. In the past 30 years, we've begun to understand. To transform a moment into an actual short-term memory, we store that memory in pieces — each piece stored in a different brain region. The different pieces contain the sight, the sound, the emotional reaction we had at the time, the place that it happened, and when it happened relative to other memories. Collectively, all of these pieces of the memory are knitted together into a what is called a memory engram — a coherent combination of all the pieces. The "knitting" is accomplished by strengthening the connections between brain cells: moments judged important prompt stronger connections.

To recall a specific memory, a part of the brain called the hippocampus retrieves the engram, the index of the different brain regions where the pieces of that memory are stored.

Recent experiments in mice show that if the hippocampus is temporarily impaired, access to a memory will be temporarily lost: the hippocampus briefly "forgets" the engram that links together the pieces of the memory. But the memory is still there, stored away in those brain regions. When this research was published, some wondered if it meant that some lost memories could be restored in humans.

A cognitive scientist, my colleague Dr. Andrew Budson, says there are two ways that memories can be "lost" as we get older. One is simply that we haven't found the right cue to access the memory. With the right cue — seeing the right person, hearing the right music, or smelling the right odor — we can suddenly recall the entire memory. The memory engram is intact. But memories can also degrade over time, which unfortunately happens to most old memories. Most lost memories in Alzheimer's disease and other dementias are degraded and probably can never be retrieved.

We are beginning to understand the physical and chemical connections that occur in the brain when memories are formed and recalled. Memory isn't magic: science is figuring it out. That's exciting. But not as exciting as being able, whenever I want, to summon the memory of my wife's face at the moment we were wed.

— Anthony L. Komaroff, M.D.
Editor in Chief, Harvard Health Letter

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