Sunday, February 24, 2008

A taste of madeline -- a sort of reprise

I wanted to write on the volatility of memory at age 71 -- a subject of considerable interest to myself and my spouse -- and searched my computer's hard drive for previous musings on the subject. (One has a tendency to repeat oneself at this age.) Lo and behold, here, just over a year ago, was exactly the essay I now wanted to write. Completely forgotten.

My wife and I sat at the dinner table last evening trolling trough memories of our 50 years together. We were astonished at some of the trivial stuff we remembered, but aware too of whole epochs of experience that have evaporated into forgetfulness.

"Too much life, not enough disk," said my wife. She suggested that the human brain evolved when an average lifetime was a only few decades. Now that we live two or three times longer, we just don't have the gigabytes to store it all.

There may be something to that, since remembering past experiences -- crocodiles in the river -- can clearly have survival value. But it's hard to see how natural selection would work to keep every little thing in the archives. Just before my mother died at age 92 she could still recite long poems by Longfellow, Whittier, Riley, Lowell, and the rest. Not much Darwinian advantage there, but it gave her considerable pleasure. Amazing that all those musty poems were somehow squirreled away in a tangle of her neuronal snapyses.

The human brain contains 100 billion neurons, and each neuron is in contact with a thousand others, more or less. If we think of each connection as being "on" or "off" (a crude simplification), then we can say that the human brain stores roughly 5,000 gigabytes of information (the equivalent of 5,000 billion keyboard characters). I'm not sure I did the calculation right, but that's more than enough capacity to store every poem you ever learned plus enough copies of Proust's Remembrance of Things Past to fill a library.

Still, memories slip away. And, when the power goes off, it is lost forever. Which is why we resort to diaries, scrapbooks, photo albums, souvenir collections. More publicly, we have memoirs, autobiographies, homepages, blogs. The internet has become willy-nilly the collective memory of our species. How vulnerable are our wikiselves to evaporation? I have piles and piles of floppy disks around the house that will never be read again.

There was one more thing my wife said last evening that I wanted to add. Now let's see, what was it? It's just at the tip of my tongue.

To this I would now add the following observation. It is altogether conceivable that as scientists discover the causes of senescence, human lifetimes will be greatly extended, perhaps -- in the absence of disease and accident -- indefinitely. It's not for me to say whether this is a desirable development; if it can happen, it will happen. But if the memory capacity of the brain is intrinsically limited, it is hard to imagine how it can be biologically increased. So the longer we live, the more of our past will be forgotten. Our physical lifespans will be extended, but our remembered lifespans will remain essentially what they are now.

"Deciding to remember, and what to remember, is how we decide who we are," wrote Robert Pinsky, America's longtime poet laureate. It is an attractive, oft-quoted formulation, but I'm not sure that it works. Pinsky is four years younger than me, but at my age deciding what to remember seems like a happy privilege. I don't "decide" who I am; I am whatever has been inexplicably retained in my overcrowded tangle of neural webs.

There was a time when we decided what photographs to put in the family albums, what clippings to paste in the scrapbook, what momentos and love letters to stuff in that box in the attic that we might open a few decades hence. Much of that analog archive has now been replaced by digital photos, e-mail, blogs. How much of this will survive the constant upgrading of computer hardware and software remains to be seen. I suspect not much. I look at the hundreds of unreadable floppy disks around the house and see a part of "who I am" that has vanished into the realm of meaningless 1s and 0s.

So we are back to what is contained retrievably in that softball-sized knot of meat at the top of the spine.

What never ceases to amaze is the volume of stuff that's stored there, increasingly beyond recall. It appears in dreams, like faint echoes of distorted sound, never quite vivid enough to drag into consciousness. One wakes with a sense of having visited the past, but with no clear notion of when or where.

Forgetfulness may be a strategy of evolution to keep us from having to carry around a paralyzing burden of past experience. I wish I could decide what to remember and what to forget, but nature seems to have a hand in the writing and erasing. Pinsky is surely right that what we remember is a big part of who we are, but he may be overestimating the extent to which who we are is under our conscious control.

Discuss this essay and more over on the Science Musings Blog.