Claustrophobic, with wacky characters and some bad acting, Monstrosity a.k.a. The Atomic Brain (1964) has all those elements of which good/bad B movies are made.
The story begins with Doctor Frank seeking dead bodies in graveyards, which he plans to use to perfect his experiment: transplanting brains. He is assisted with the heavy lifting in this arduous task by a dog-faced mutated product of one of his tests, in which he transplanted an animal brain inside the man.
The Doctor is hired by Mrs. March, a bitter old woman who desires to have her brain placed in a nice, young attractive body. Her immense wealth makes it possible for the Doctor to continue his work unfettered.
A sophisticated radioactive laboratory is constructed.
The doctor begins by re-animating the corpse of a young woman, whose body he had swiped from the cemetery.
This being a test, she does not have brain function and just wanderers around like a zombie, constantly staring blankly forward.
In order for the real deal to work, the Doctor requires living subjects. So, Mrs. March places an advertisement for a housekeeper and three young ladies apply.
Upon arrival, the Doctor gives them all very thorough physical examinations and the sexiest, most glamorously perfect girl is chosen.
The other two girls are forced to stay, so word can not leak out to the authorities. They try escaping several times, but their attempts are always thwarted.
Time is running out. The Doctor is gaining confidence and making preparations. Mrs. March is getting impatient, anxious to get her new youthful body. And the girls desperately need to come up with a plan...
Monstrosity (The Atomic Brain)- intro