Smart Genes?

(2 of 6)

Therapeutic promise is only one key implication of the new research. More immediate, and for now more important, is that the work gives neurobiologists further evidence about what memory is and how it works--a mystery whose secrets have been slowly unfolding for decades.

One thing has become clear to scientists: memory is absolutely crucial to our consciousness. Says Janellen Huttenlocher, a professor of psychology at the University of Chicago: "There's almost nothing you do, from perception to thinking, that doesn't draw continuously on your memory."

It can't be otherwise, since there's really no such thing as the present. As you read this sentence, the sentence that went before is already a second or two in the past; the first line of this story went by minutes ago. Yet without a memory of what's been said, none of what you are now reading makes the slightest sense. The same is true for our lives as a whole. Memory provides personal context, a sense of self and a sense of familiarity with people and surroundings, a past and present and a frame for the future.

But even as psychologists and brain researchers have learned to appreciate memory's central role in our mental lives, they have come to realize that memory is not a single phenomenon. "We do not have a memory system in the brain," says James McGaugh, director of the Center for the Neurobiology of Learning and Memory at the University of California, Irvine. "We have memory systems, each playing a different role."

When everything is going right, these different systems work together seamlessly. If you're taking a bicycle ride, for example, the memory of how to operate the bike comes from one set of neurons; the memory of how to get from here to the other side of town comes from another; the nervous feeling you have left over from taking a bad spill last time out comes from still another. Yet you are never aware that your mental experience has been assembled, bit by bit, like some invisible edifice inside your brain.

And brain researchers might never have picked up on the fragmentary nature of memory without their studies of people whose memory has been damaged by illness or injury. The most celebrated such individual is H.M. In 1953, when he was 27, he had drastic brain surgery to cure severe epilepsy. The operation cured his epilepsy, but removing parts of his brain's temporal lobes, including a structure called the hippocampus, destroyed his ability to form new memories. H.M., who is still alive, has a reasonably good short-term memory. Once introduced to a visitor, he will remember the person's name and other information while a conversation lasts. But if the visitor leaves and returns, H.M. has no memory whatsoever of having met the person. In fact, H.M. has no permanent memory of anything that happened after his surgery. As far as he's concerned, it's still 1953, and that old man looking back at him from the mirror bears only a passing resemblance to the young man he knows himself to be.

That sort of impairment has convinced scientists that the medial temporal lobe and hippocampus are key in transforming short-term memories into permanent ones, and also that permanent memories are stored somewhere else; otherwise, H.M. would have lost them too.