memory and forgetting

Remembering the future.

Easy to see that when you contemplate the future, the past is all you really have to go on. So I was intrigued by a piece in Nature, a year or so ago now, suggesting that the way we build memories may be specifically tailored to allow efficient generation of situations yet to come.

Psychologists Daniel Schachter and Donna Addis of Harvard University note that memory seems to work by storing many separate pieces of past experience. Recollections of past episodes are then assembled by adding together bits of information which seem to be related.

This seems puzzling because it makes memory unreliable in crucial ways. We may recall seeing two people in a particular scene at the same time when in fact we originally noticed them on separate days, for example. So why can’t our brains have a memory system which is more like a videotape, and can simply be replayed to recapture the scene correctly?

Schachter and Addis suggest that the videotape would be less useful for imagining the future. We are trying to anticipate events which will not exactly repeat the past, but will be something like it – whether we are imagining a board meeting, a battle, a job interview or a date. A memory system which allows a person to review sketches of past events, and recombine them to imagine new ones is a more flexible guide to possible futures, even though it makes mistakes in pure recollection.

This idea, they say, is backed up by several lines of research. Amnesiacs sometimes lose their future as well as their past. Some deeply depressed people have little specific grip on the past or the future. And neuroimaging shows activity in the same regions of the brain when the people being scanned are remembering past episodes or imagining future ones. Specific experiments to test it, however, lie in the future. When there’s time, I must check to see if any have been reported yet.

Nature, 445, 4 January 2007, p27.

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