Saturday, December 13, 2008

And if you took the synapses...

Out walking on a blustery Sunday afternoon the lyrics of a song popped into my head. I sang out loud:
If I sent a rose to you
For every time you made me blue
You'd have a room full of roses.
It must have been the early 1950s when I last heard that song, as a young teenager, probably listening to the Grand Ole Opry on my little Sears Silvertone radio. I couldn't remember who sang it, but I could hear his voice in my head.

And I fell again into one of those moments of wonderment at the seeming miracle of memory.

The lyrics, the tune, the voice. All somehow stored in my head for nearly 60 years. Along with an astonishing amount of other stuff. Experiences. Voices. Images. Learned knowledge. How? No one knows for sure.

The human brain contains approximately 100 billion neurons, and each neuron is in contact with a thousand others, more or less, through a cobwebby tangle of synapses. 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 (did I do the calculation right?). The hard disk of my MacBook Pro has 186 gigabytes of memory of which I am currently using 30. I have stored a huge music collection, a few thousand photographs, and millions of words, not to mention a heap of applications. So it's no miracle to imagine all that stuff stored in the brain.

But how? With what sort of encoding? How are memories "read" without erasing? How does the brain know not to "write over" crucial memories? We know how this works in computers, but how in the brain? An article in the 4 December issue of Nature describes some of the remarkable progress researchers are making in understanding how long-term potentiation of synaptic transmission occurs. The molecular biology is breathtaking.

Where memory fails, there's always Google, the collective memory of our race. I Google "Roomful of Roses." Within a few seconds I know that all those years ago I was listening to country singer George Morgan, singing a song written in the 1940s by Tim Spencer of the Sons of the Pioneers. I close my eyes and other lyrics of the song come bubbling up out of the cobwebby neural tangle:
And if you took the petals
And you took them all apart
You'd be tearing at the roses
Just the way you tore my heart.