Everywhere in the snarl of tissues that is the brain, chemicals whip down fibers, tear across cell divides, and continue pell-mell on their Gordian rounds. One hundred billion individual nerve cells — each reaching out in turn to as many as 200,000 others — diverge, reverberate and converge into a webwork of staggering complexity. This three-pound thicket of gray, with its thousands of distinct cell types and estimated one hundred trillion synapses, somehow pulls out order from chaos, lays down the shivery tracks of memory, gives rise to desire or terror, arranges for sleep, propels movement, imagines a symphony, or shapes a plan to annihilate itself.

— Kay Redfield Jamison, Night Falls Fast: Understanding Suicide