Hearing voices in one’s head is a hallmark symptom of schizophrenia. Those auditory hallucinations are caused by overstimulation in the brain regions that process sound. But when the inner voices start talking, the brain fails to respond to real voices. Biological psychological scientist Kenneth Hugdahl and his research team identified this paradox when they had hallucinating patients listen to sounds through headphones and measured their brain activity using neuroimaging technology, in addition to psychological measures. They found that the heightened brain activity that is associated with vocal hallucinations simultaneously douses the perception of real sounds. This explains why schizophrenia patients seem shut off from the outside world. Hugdahl’s team is testing ways to help schizophrenia patients focus on outside voices when the inner voices are active.