The Brain Tank is a weapon designed by Dr. Caligosto Loboto during the course of Psychonauts in cooperation with Coach Oleander's plot to take over the world. These tanks are used to harness the psychic powers of the stolen campers' brains and convert the power into psychic blasts.
The blueprint of this brain tank is encountered as a boss fight at the end of the Brain Tumbler Experiment which is used by the brain of Dogen instead of Oleander, however, the blueprints for it can be found at the end of Basic Braining. Razputin encounters another in the Thorney Towers Home for the Disturbed, operated by Oleander. Oleander's PSI powers are much more advanced than when he was in his human state. During the fight, Razputin's brain is sneezed out, and eventually makes its way to the tank, where it converges with Oleander's, creating the Meat Circus mental world, and forcing him into the mental worlds.
The tank is an armored vehicle that has spikes on it. The brain is suspended by a claw and is inside a bullet-proof glass dome filled with green goo. There are no man-made weapons on these tanks, but instead they have psychic powers generated from the brain.