The Brain That Wouldn’t Die (1962)

“Brilliant but borderline psychotic surgeon does secretive, experimental work with limb transplants and tissue rejection drugs, much to the chagrin of his surgeon-father. When he crashes his car and his fiancee is decapitated, his research – far from complete – is put to the test. His focus then becomes finding an appropriate donor body to make his fiancee whole, while the current and failed experiments in his basement laboratory grow restless.” -imdb.com