Hearing voices Hearing voices when there are none to be heard is a classic symptom of mental illness. But very little is known about how or why this intriguing sensation – that of an internally generated ‘stimulus’ which appears to originate from outside the body – arises. Now Thomas Dierks of the Johann Wolfgang Goethe Universitüt, Frankfurt, Germany, and colleagues announce in the March issue of Neuron that there seems to be a clear neurological explanation for the distinctive ‘realness’ of auditory hallucinations.
Using a brain-scanning technique called functional magnetic resonance imaging (fMRI), the researchers have found that the brain areas involved in understanding as well as generating speech are the same ones that exhibit increased activity [as measured by increasing blood flow] when people feel that they are hearing voices. Dierks’ team worked with three schizohphrenic patients who were able to signal the beginning and end of their hallucinations, and who experienced hallucinations lasting only a couple of minutes at a time. They found that when these subjects reported themselves to be hearing voices, or when they were played real sounds, metabolic activity consistently increased in, amongst other places, the part of their brains known as ‘Heschl’s gyrus’; a region known to be involved in the perception of hearing.
This is interesting because other studies have shown that when patients are asked to imagine sounds or to imagine themselves to be speaking, Heschl’s gyrus does not light up. In addition, Dierks’ group showed that the anterior insula, a part of the brain thought to participate in generating verbs, also appeared to be involved in the auditory hallucinations experienced by these three schizophrenics. Even more fascinating is the fact that, while imagining that they were hearing voices, the two right handed patients in the study had markedly more activity overall in their language-dominant brain hemisphere – that is, the left hemisphere – than in the right side of their brains. Conversely, the left-handed schizophrenic exhibited a right-hemisphere bias. However, while the researchers admit that this result, “is suggestive of a particular role for the language-dominant hemisphere,” the researchers are quick to point out that their tiny sample size forbids them from drawing, “any strong conclusions,” from this observation. So although these findings in no way explain what makes some people hear voices, they do shed light on the reasons why for some people, non-existent sounds can appear to be so real. Source: Nature (UK), 22nd April 1999