Donovan's Brain, Curt Siodmak

Scientist Patrick Cody is focused only on his research. He has no time for emotions. So when a dude conveniently dies on him, he takes the guy's brain with no hesitation.

Cody hooks the brain up to some equipment that keeps it alive and begins to work on the problem of communication. When he strengthens the electrical current and the brain's food, he begins to get weak telepathic communications.

But as the brain grows stranger, it begins to take over Cody's body.

Interesting.