Brain scans seek roots of imagined voices.

Many people suffering from schizophrenia endure periods in which they hear disembodied voices, often uttering such scathing comments as "You're worthless" or "No one likes you." Hallucinations of this kind are amplified by breakdowns in two areas of the brain that monitor the nature and source of what one says silently to oneself, a new study suggests.

"A predisposition to [hearing voices] might depend on abnormal activity in brain areas implicated in perceiving inner speech and in determining whether it is of self or alien origin," contend Philip K. McGuire of the Institute of Psychiatry in London and his colleagues.

Researchers have assumed that auditory hallucinations arise when a person lacks conscious awareness of verbal thoughts as they occur or attributes such thoughts to someone else. McGuire's group offers clues to the biology of these errors. Defective communication between a brain region fostering the "mind's voice" and another abetting the "mind's ear" underlies the experience of hearing disembodied voices, in their view.

Schizophrenia, a severe disruption of thought and personality that stems from poorly understood brain disturbances, often includes hallucinations and delusions. Social withdrawal, apathy, and incoherent trains of thought also feature prominently in this condition.

McGuire's group used positron emission tomography (PET) scans to measure blood flow in the brains of six men diagnosed with schizophrenia who frequently heard voices, six schizophrenic men who had rarely or never heard voices since their illness began, and six healthy men who had never heard voices and had no psychiatric disorders in their families.

The researchers obtained PET scans while participants mentally recited a series of written sentences in their own voice and when they imagined a second set of sentences being spoken by an unknown voice they had previously heard on a tape. No one suffering from schizophrenia hallucinated during the experiment.

The three groups displayed comparable blood flow patterns throughout their brains while thinking of sentences in their own voice. However, when imagining sentences in another person's voice, hallucinators showed reduced blood flow in the supplementary motor area (SMA) and the left middle temporal gyrus (MTG), the scientists report in the Sept. 2 Lancet. In contrast, nonhallucinators and controls exhibited roughly equal blood flow boosts in those areas during the same task.

The SMA helps to initiate movements needed to speak. Reduced blood flow in the SMA of hallucinators imagining someone else's voice may block the "mind's ear" and create a "less secure appreciation" of where the voice originated from, McGuire and his coworkers argue.

The left MTG helps to monitor the "mind's voice," they contend, since it livens up on tasks that require thinking about speech but calms down during talking. Lowered activity in this area for hallucinators imagining another voice suggests that their brains respond as if they were speaking aloud, the scientists assert. It remains unclear whether the observed brain changes predispose hallucinators to hearing voices or simply take part in hallucinations and tasks that simulate them, such as imagining another's voice, cautions Richard Jed Wyatt, a psychiatrist at the National Institute of Mental Health's neuroscience center in Washington, D.C.