Tuesday, March 13, 2007

I am, therefore I think

How this fellow got himself stranded on the sand, I don't know, but if my sister hadn't pulled me aside I would have squished him with my bare foot. A spotted sea hare, Aplysia dactyolmela. A worthy creature, as I shall now disclose, of estimiable value to science. We put him back in the sea where he quickly revived, flapping his mantle wings as if he wanted to fly.

The 2000 Nobel Prize in medicine went to Eric Kandel, Paul Greengard, and Arvid Carlsson for studies on the physiology of memory. In his address to the Nobel Foundation, Kandel recounted his evolution as a scientist.

He first became interested in the study of memory in 1950 as a result of his readings in psychoanalysis as an undergraduate at Harvard. Later, as a medical student, he began to find psychoanalysis limiting; it treated the brain as a black box, observable only from outside. Kandel wanted to open the box, to see what was inside -- to explore the mansion of memory as flesh and blood.

He was convinced that memory was biological and that human memory might have much in common with memory in other organisms. His approach, therefore, would be reductionistic: Start with the rudiments of memory in a simple organism, with the hope of eventually understanding the apparent miracle of human memory.

Kandel took Aplysia as his model. This shell-less aquatic snail has several advantages as an experimental animal: It has only 20,000 central nerve cells, rather than the tens of billions in mammalian brains, and the cells are big, ten times larger than human neurons. And Aplysia can be trained to respond to stimuli. It learns and remembers.

When a sea snail remembers, changes happen at the places where nerve cells touch each other, the synapses. Kandel, and others, worked out the biochemistry of these changes, for both short-term and long-term memory, and showed that the cellular and molecular changes at work in Aplysia's rudimentary brain are present in mammals too.

There may be as many as 100 billion nerve cells in the human brain, and each one is connected to thousands of others. Memories are stored as electrical and chemical changes at the synapses where cell communicates with cell. A scribble. A lifetime of experiences scribbled into flesh.

As Kandel pointed out in his Nobel address, there is lots more yet to learn, and full understanding of human memory will require the combined efforts of molecular biologists, cognitive psychologists, neurologists, psychiatrists, and perhaps even computer modelers. The 21st century promises to be the century when we explore every corner of the human brain, and understand, at least in principle, how a brain gives rise to mind.

The sea snail Aplysia has helped confirm that Descartes was wrong; the human self is not a dualism of mind and matter, but rather an efflorescence of self from matter, a shimmering exuberance of the stuff of the universe gathered in the human brain into biochemical webs of astonishing complexity. Not "I think, therefore I am," but rather "I am, therefore I think."