At the Museum of Hoaxes there's a section called "The 20 Most Bizarre Experiments of All Time" which includes the one giving title to this entry, ranked at number 4:
In 1954 James Olds and Peter Milner of McGill University discovered that the septal region is the feel-good center of the brain. Electrical stimulation of it produces sensations of intense pleasure and sexual arousal. They demonstrated their discovery by inserting wires into a rat's brain and then showing that when the rat figured out it could self-stimulate itself by pressing a lever, it would maniacally bang on that lever up to two-thousand times an hour. (The image at the very top of this page, third from the right, shows one of Olds and Milner's rats banging on its lever.)
In 1970, Robert Heath of Tulane University dreamed up a far more novel application of Olds and Milner's discovery. Heath decided to test whether repeated stimulation of the septal region could transform a homosexual man into a heterosexual.
Heath referred to his homosexual subject as patient B-19. He inserted Teflon-insulated electrodes into the septal region of B-19's brain and then gave B-19 carefully controlled amounts of stimulation in experimental sessions. Soon the young man was reporting increased stirrings of sexual motivation. Heath then rigged up a device to allow B-19 to self-stimulate himself. It was like letting a chocoholic loose in a candy shop. B-19 quickly became obsessed with the pleasure button. In one three-hour session he pressed it 1500 times until, as Heath noted, "he was experiencing an almost overwhelming euphoria and elation and had to be disconnected."
By this stage of the experiment B-19's libido was so jacked up that Heath decided to proceed with the final stage in which B-19 would be introduced to a sexually-willing female partner. With permission from the state attorney general, Heath arranged for a twenty-one-year-old female prostitute to visit the lab, and he placed her in a room with B-19. For an hour B-19 did nothing, but then the prostitute took the initiative and a successful sexual encounter between the two occurred. Heath considered this a positive result.
Little is known of B-19's later fate. Heath reported that the young man drifted back into a life of homosexual prostitution, but that he also had an affair with a married woman. Heath optimistically decided that this showed the treatment was at least partially successful. However, Heath never did try to convert any more homosexuals.