The Brain that Wouldn't Die (1962)

Directed by Joseph Green. The story revolves around Dr. Bill Cortner, a brilliant but morally questionable surgeon who, after a car accident that leaves his fiancee Jan Compton decapitated, becomes determined to keep her alive. He manages to keep her head alive in a laboratory while searching for a suitable body to transplant it onto. As Jan struggles with her gruesome existence, Cortner descends into increasingly unethical and macabre experiments, ultimately leading to horrifying consequences.