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December 09, 2004
Voices and the brain
Temporal course of auditory hallucinations.
Shergill SS, Brammer MJ, Amaro E, Williams SC, Murray RM, McGuire PK.
Background: Researchers are still unclear about why voices or “auditory verbal hallucinations” occur in schizophrenia. Some think that voices are due to a person’s own inner speech that gets misperceived as sounds that come from outside. Others think that it is because of extra activity in a particular part of the brain known as the auditory cortex (which is responsible for hearing and language). Brain imaging helps take pictures of the brain while someone is thinking or even while hallucinating. Some of this imaging work has found that areas that are involved in both speech generation and perception get activated during auditory verbal hallucinations, but the sequence in which these areas get activated remains unclear. So, the current study used a type of brain imaging known as functional magnetic resonance imaging (fMRI) to look at how brain activity that is thought to be involved with voices in schizophrenia changes while someone is having auditory hallucinations.
Method: This study was conducted in London, England. The researchers asked 8 people with schizophrenia who frequently heard voices to give permission to have their brain scanned while they heard voices. They were able to get brain images of hallucinations for only 2 of the 8 patients. The first participant was 47 years old with a 22-year history of illness, and was being treated with Clozaril, Solian and Sodium valproate. The second was 26 years old, had a 6-year history of illness and was being treated with Zyprexa. In both cases the hallucinations involved people making derogatory remarks to the person. The participants were asked to lie in a brain scanner and press a button each time a auditory hallucination started and to release the button when it stopped. This was repeated for every hallucination they experienced during the 5 min session.
Results: They found that each auditory verbal hallucination lasted an average of 16 seconds with a range of 3–42 secs. They found specific areas of the brain were activated 6–9 secs before the person signalled the onset of the hallucination. These were areas that are involved in generation of inner speech (left inferior frontal, right middle temporal gyri). Different areas of the brain, which are involved in perception of auditory material or hearing, were active once the person became aware of the hallucination (bilateral temporal gyri, left insula).
Interpretations & Limitations: These results supports the hypothesis that when a person hears voices, there is activation in brain regions that are involved in generating inner speech which occurs before activation in areas that help us understand or perceive a sound. Overall, this study argues that hallucinations are due to the misidentification of self-generated verbal material and that different areas of the brain are involved at various times during the hallucinations. However, as with most studies that have tried to image the brain during hallucinations, the size of the group that was studied is very small. It is difficult to say with certainty whether the results obtained from these 2 participants will extend to all those who hear voices. Also, the researchers used a type of scanner (1.5T) that is not as sensitive as other more powerful scanners, so there maybe be other regions of the brain that are involved in voices that may not have been properly picked up in this study. Nevertheless, they provide some interesting insights into what happens in the brain when people hear voices.
The researchers are supported by the Wellcome Trust and the National Alliance for Research on Schizophrenia and Depression.Posted by Farzin at December 9, 2004 03:10 PM | TrackBack