The brain's voices: comparing nonclinical auditory hallucinations and imagery

Although auditory verbal hallucinations are often thought to denote mental illness, the majority of voice hearers do not satisfy the criteria for a psychiatric disorder. Here, we report the first functional imaging study of such nonclinical hallucinations in 7 healthy voice hearers comparing them with auditory imagery. The human voice area in the superior temporal sulcus was activated during both hallucinations and imagery. Other brain areas supporting both hallucinations and imagery included fronto temporal language areas in the left hemisphere and their contralateral homologues and the supplementary motor area (SMA). Hallucinations are critically distinguished from imagery by lack of voluntary control. We expected this difference to be reflected in the relative timing of prefrontal and sensory areas. Activity of the SMA indeed preceded that of auditory areas during imagery, whereas during hallucinations, the 2 processes occurred instantaneously. Voluntary control was thus represented in the relative timing of prefrontal and sensory activation, whereas the sense of reality of the sensory experience may be a product of the voice area activation. Our results reveal mechanisms of the generation of sensory experience in the absence of external stimulation and suggest new approaches to the investigation of the neurobiology of psychopathology.