Hugh Pickens writes: "Have you even "known" something was true that later turned out to be mistaken? Our memories are not always trustworthy but recent research shows that vivid false memories that may seem indistinguishable from true memories may be processed by different parts of the brain. Using an MRI, the study showed (pdf) that when participants had confidence in their answer and they were correct, blood flow increased to the medial temporal lobes containing the hippocampus, important for memory. When subjects had confidence in their answer but were wrong, the frontoparietal region lit up, a region of the brain associated with a "sense of familiarity." The research could one day be used to devise an early test for Alzheimer's disease, or to assess the accuracy of witness testimony and underscores the fact that judges and juries should not use a witness's confidence in their own answers as a signal that the answers are more likely to be true. "It is really surprising, but there is a very weak relation between accuracy and confidence," says Valerie Reyna, a cognitive neuroscientist at Cornell University."