I heard Alvin Plantinga say recently that this is one of those things that makes the life of a philosopher difficult – spending your days thinking about what it’s like to be a brain in a vat. But the term has a long and venerable history.
Contemporary counterpart of Descartes’s hypothesis that one’s beliefs are induced by an evil genius.
Used within a premiss in arguments for scepticism, the hypothesis says that nothing exists except one’s brain—in a vat, in order that its electrochemical activity should be sustained—so that whatever may seem to one to be the case, its seeming so is accounted for by such activity alone.
The sceptic invites one to say “For all I know, I am a brain in a vat, and there is no external world.”
Brains in vats are introduced also in philosophy of mind in connection with the idea that a person’s psychological faculties require nothing but a brain’s operations.
Prof. Jennifer Hornsby, The Oxford Companion to Philosophy (Oxford, 1995), 102.