This is a podcast from the archives of the BBC Reith Lectures.

This lecture in the series Mechanics of the Mind, given by Colin Blakemore, was originally broadcast in 1976.

Imagine that you're asked to remember the number, 584. What could be easier?

Whether you wanted to or not, the number would be yours to recall for the next few minutes.

With the slightest effort of will, you could remember it at the end of this lecture, and if it were

important enough, you would recollect it next month, next year, or next century.

There's an American, I'll call him Henry M, who's been robbed of this precious power to remember,

not partially and gradually just by growing old, as most of us will be, but suddenly and almost

totally, by the knife of a well-intentioned surgeon. From Henry, we can learn about the nightmare

of eternal forgetfulness, a condition that France Kafka would have been delighted to describe.

Brenda Milner, at the Montreal Neurological Institute,

has followed the case of Henry for more than 20 years.

She once asked him to remember that very number, 584.

He sat quietly, entirely undistracted, for minutes, and to her surprise he could recall the number.

But when asked how he did it, this is what he said.

It's easy. You just remember 8.

You see 5-8 and 4 add up to 17.

You remember 8, subtract it from 17 and it leaves nine. Divide

nine in half and you get five and four. And there you are, five, eight, four. Easy. Henry lives

in a world of his own, restricted not just in space, but in time. Ever since an operation on his brain

in 1953, his world has been just a few minutes long.

Without such elaborate and fantastic tricks of rehearsal, almost everything slips from his mind,

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