DONOVAN'S BRAIN, Unrated, 1953, B&W, 85 minutes, MGM/UA Home Video, $59.95. Scientist hubby explains to loyal helpmate why his experiments on monkeys are necessary. "You're right, darling, I'm being silly," she says, and he says, "Thanks dear. Now go make us one of those wonderful stews, will you?" The only reason to catch this desultory sci-fi melodrama is that it contains a costarring, if awfully subdued, performance by Nancy Davis, now Reagan, and you can have fun reading double meanings into the spousal chitchat. As when wife counsels husband, "Please, go take a nap." For most of the film, an evil millionaire's brain, kept alive in a home aquarium (the first think tank?), sends out instructions on mayhem to Lew Ayres, as the scientist, who grows suddenly cold and crabby and develops a craving for blue serge. When the puny wave of terror (mostly fiscal) is over, it sounds like a post-mortem for an administration. She: "But they can't blame you, they can't." He: "I went into this with my eyes open, but it got out of hand, and I did many foolish things -- things that made other people suffer." Right. Now how about that stew?