Cerebral blood flow in subjects with social phobia during stressful speaking tasks: A PET study

Objective: The central nervous system representation of social phobia (soci al anxiety disorder) is largely unknown. The aim of this study was to exami ne brain activity during symptom provocation in social phobics. Method: Positron emission tomography with the use of O-15 water was used to measure regional cerebral blood flow (rCBF) in 18 subjects with DSM-IV-def ined social phobia and a nonphobic comparison group while they were speakin g in front of an audience and in private. Heart rate and subjective anxiety were also recorded. Results: During public versus private speaking, subjective anxiety increase d more in the social phobics than in the comparison group. increased anxiet y was accompanied by enhanced rCBF in the amygdaloid complex in the social phobics relative to the comparison subjects. Cortically, brain blood flow d ecreased in the social phobics and increased in the comparison subjects mor e during public than private speaking in the orbitofrontal and insular cort ices as well as in the temporal pole and increased less in the social phobi cs than in the comparison group in the parietal and secondary visual cortic es. Furthermore, rCBF increased in the comparison group, but not in the soc ial phobics, in the perirhinal and retrosplenial cortices. Conclusions: An rCBF pattern of relatively increased cortical rather than s ubcortical perfusion was observed in the nonphobic subjects, indicating tha t cortical evaluative processes were taxed by public performance. In contra st, the social phobia symptom profile was associated with increased subcort ical activity. Thus, the functional neuroanatomy of social phobia involves the activation of a phylogenetically older danger-recognition system.