Aims Placebo effects on anxiety are often observed in daily psychiatry practice, but the biological neural basis is not well understood. We investigated the effects of lorazepam and a placebo on cerebral response during listening to emotional vocal sounds.
Methods Using the event-related design, 28 control subjects were scanned by functional MRI while listening to emotional vocal sounds in non-drug, placebo, and lorazepam conditions. After scanning, subjects rated their levels of reduced anxiety under lorazepam and placebo conditions. We examined the correlation between ratings of reduced anxiety and cerebral responses.
Results Compared with non-drug condition, cerebral activation was significantly reduced in the bilateral inferior frontal gyrus (IFG) and anterior insula under placebo condition as well as lorazepam condition. Compared with lorazepam condition, cerebral activation in placebo condition was significantly increased in the left BA8 region. Further, significant positive correlation was shown between ratings of reduced anxiety and cerebral activation in bilateral IFG and the left BA8 region.
Conclusions Our results suggest that cerebral response in bilateral IFG and anterior insula is closely related to common anti-anxiety effect of both placebo and lorazepam. Increased left BA8 activation compared with lorazepam may reflect the anti-anxiety effect of placebo.
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