When individuals experience auditory hallucinations, the primary auditory
cortex seems to be involved.
Yet the question remains as to how.
For some time now, it has been known that when a person pays attention to
external sounds, the electrical activity of neurons in the primary auditory
cortex increases, and that, conversely, when a person's attention is
distracted from external sounds, then electrical activity of neurons in this
brain region decreases. So Daniela Hubl, M.D., of the University Hospital for
Clinical Psychiatry in Bern, Switzerland, and colleagues hypothesized that if
the electrical response of primary auditory cortex neurons increases during
auditory hallucinations, then it is a nonspecific auditory response to those
hallucinations, but if the electrical response of those neurons during
hallucinations decreases, the electrical response is a constituent of the
hallucinations per se.
They tested their hypothesis on seven individuals who experienced periodic
auditory hallucinations even though the individuals were on antipsychotic
medications. Subjects sat in a slightly darkened room in a comfortable resting
position. External auditory stimuli (tone pulses) were presented to both ears
of each participant by insert phones for about eight minutes. During that time
participants were also instructed to listen for their inner voices and to
indicate the beginning as well as the end of them by pressing a button.
Throughout the recording period, the electrical activity of primary auditory
cortex neurons was measured in each participant with an
Hubl and her group then compared the electrical response of primary
auditory cortex neurons during hallucinations with the response of those
neurons during nonhallucination periods. In each subject the scientists found
a statistically significant reduction in neuronal electrical response during
hallucinations compared with the response during nonhallucination periods.
So, since there was a decrease rather than an increase in primary auditory
cortex activity during hallucinations, this activity was an actual constituent
of those hallucinations, the researchers concluded in the January British
Journal of Psychiatry.
Moreover, they reported, the decreased primary auditory cortex activity
during hallucinations was localized mostly to the left side of the brain. The
left auditory cortex is known to be an essential part of the brain's language
system, which further encompasses Wernicke's area and the motor speech areas
of Broca, as well as their interconnections.
The study was funded by the Swiss National Science Foundation.
An abstract of "Competition for Neuronal Resources: How
Hallucinations Make Themselves Heard" is posted at<http://bjp.rcpsych.org/cgi/content/abstract/190/1/57>.▪