The opening of “From Cooling System to Thinking Machine,” Carl Zimmer’s excellent Being Human essay about historical attempts to understand brain function, from anatomical experiments to thought experiments:

“Hilary Putnam is not a household name. The Harvard philosopher’s work on the nature of reality, meaning, and language may be required reading in graduate school, but Putnam’s fame hasn’t extended far beyond the academy. But one of Putnam’s thought experiments is familiar to millions of people: what it would be like to be a brain in a vat?

Here’s how Putnam presented the idea in his 1981 book, Reason, Truth, and History:

Imagine that a human being…has been subjected to an operation by an evil scientist. The person’s brain…has been removed from the body and placed in a vat of nutrients which keeps the brain alive. The nerve endings have been connected to a super-scientific computer which causes the person whose brain it is to have the illusion that everything is perfectly normal. There seem to be people, objects, the sky, etc.; but really, all the person…is experiencing is the result of electronic impulses travelling from the computer to the nerve endings.

Philosophers have wondered for thousands of years how we can be sure whether what we’re experiencing is reality or some shadowy deception. Plato imagined people looking at shadows cast by a fire in a cave. Descartes imagined a satanic genius. Starting in the 1960s, philosophers began to muse about what it would be like to be a brain in a vat, with reality supplied by a computer. The story circulated in obscure philosophy journals for over a decade before Putnam laid it out in his book.” (Thanks Browser.)