On "New Explorers" on PBS, 2/18/92: According to a brain surgeon who does "hemispherectomies" to treat severe seizures: I had one little girl as a patient who told knock-knock jokes; we removed her left brain and she still told knock-knock jokes. I had another little girl as a patient who told knock-knock jokes; we removed her right brain and she still told knock-knock jokes. So I have to conclude that knock-knock jokes aren't in the brain.
(From the "Rest" of RHF)