Friday, March 05, 2010

Thinking about thinking

Nothing we know about in the universe approaches the complexity of the human brain. What is it? A vast spider web of neurons, cells with a thousand octopuslike arms, called dendrites. The dendrites reach out and make contact at their tips with the dendrites of other cells, at junctions called synapses.

A hundred billion neurons in the human brain, with an average of 1,000 dendrites each. A hundred trillion octopus arms touching like fingertips, and each synapse exquisitely controlled by the cells themselves, strengthening or weakening the contact, building webs of interlinked cells that are knowledge, memory, consciousness -- a soul, a self.

A hundred billion neurons. That's more brain cells than there are grains of salt in 1,000 one-pound boxes of salt. A roomful of salt grains, floor to ceiling. Each in contact with hundreds, thousands, or tens of thousands of others. The contacts flickering with variable strength. Continuously. Unconsciously. Never ceasing. Remembering. Forgetting. Feeling joy. Feeling pain. Thinking. Speaking. Lifting a foot, moving it forward, putting it down again. Flickering. A hundred trillion flickering synapses.

Just thinking about it is exhausting.

In recent years, new scanning technologies enable neuroscientists to watch live human brains at work. Active neural regions flicker on the screens of computer monitors as subjects think, speak, recite poems, do math. Thinking -- displayed on the screen of a scanning monitor -- can look like a grass fire exploding across a prairie.

Perhaps the most exciting research is that of the scientists who study the biochemistry of neurons: How do the cells regulate synaptic connections to build new neural webs? One big surprise is just how much of the "thinking" of neurons is done by the dendrites, those hundreds of spidery arms that connect neurons to one another. DNA in a neuron's nucleus sends messenger RNA down along the dendrites to active synapses, where they are translated into proteins that regulate the strength of synaptic connections. Tiny protein factories in the dendrites are apparently key to learning and memory.

What all this amounts to is awareness of awareness. The biochemical machinery of awareness has been turned upon itself, and we begin to glimpse the astonishing architecture of the human soul.