MedWire News: Study results suggest that auditory verbal hallucinations in schizophrenia may arise as a consequence of an attenuated deactivation in the left superior temporal gyrus, an area implicated in verbal self-monitoring processes.
Previous studies have shown that patients with auditory verbal hallucinations show attenuated activation of brain regions involved with auditory processing during monitoring of inner speech.
“However, there are no functional magnetic resonance imaging (fMRI) studies explicitly comparing the perception of external speech with internal speech in the same patients with schizophrenia,” say Claudia Simons (Maastricht University, The Netherlands) and co-authors.
To investigate, the researchers recruited 15 medicated schizophrenia patients with a mean illness duration of 11.2 years and 12 healthy individuals with no history of psychiatric disorders. The participants were assessed using fMRI while they listened to spoken sentences (external speech) or imagined sentences (inner speech).
During the listening trials, the anticipated activation of the left superior temporal cortex could be seen in both controls and patients, suggesting that listening to spoken sentences is not impaired in individuals with schizophrenia.
However, controls showed a greater decrease in activation during inner speech compared with schizophrenia patients. “This provides evidence for defective self-monitoring of inner speech in schizophrenia patients,” say Simons and team.
They add: “Failure to attenuate the activity in the temporal cortex may lead to the attribution of the verbal material as being of external origin, ultimately leading to auditory hallucinatory experiences.”
In addition, inner speech trials resulted in a greater activation of the anterior cingulate gyrus than listening trials in controls. However, patients did not show activation of the cingulated cortex during inner speech.
It has been suggested that the anterior cingulate may act as a top-down modulator of left superior temporal gyrus activity. “This impaired modulation may be associated with external misattributions of inner speech,” write the authors in the journal Biological Psychiatry.
Simons and team conclude: “Our data indicate that when generating inner speech, schizophrenia patients show an attenuated deactivation in the left superior temporal gyrus, an area that’s been implicated in verbal self-monitoring processes.
“This is consistent with the notion that auditory verbal hallucinations in schizophrenia may arise as a consequence of faulty predictive models underlying the monitoring of behaviors including inner speech.”
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