In the days of rudimentary chemistry, the mind was thought to be a beaker of swirling volatile essences. Then came classical physical mechanics, and the mind was regarded as a clocklike thing, with springs and wheels. Then it was steam-driven, maybe. A combustion chamber. Then came electricity and Freud, and it was a dynamo of polarized energies—the id charged one way, the superego the other.
Now, in the heyday of the microchip, the brain is a computer. A CPU.
The early psychologists also described the mind in terms of hydrodynamics. I wonder what the next metaphor will be — I’m surprised that the brain as world wide web, full of ephemeral interconnections and communicades, between actors who rise and fall in influence and activity, hasn’t surfaced as a metaphor yet (not that such a metaphor would necessarily be any better than the old ones). Maybe that metaphor is not simple enough.
Update 2008-02-20: My friend Kelly pointed me at Your Brain Works Like the Internet, which shows that this metaphor is present in the wild.