We investigated central nervous system correlates of simple phobic fear. Regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET) in eight volunteers with symptomatic spider phobia that were exposed to visual phobogenic and neutral stimuli. Diazepam (0.1 mg/kg body weight i.v.) or placebo was administered under double-blind conditions after initial PET scans. The PET scans were then repeated. The presence of fear was confirmed by rating procedures and increased number of nonspecific electrodermal fluctuations and by higher heart rate during phobic than during neutral stimulation. Phobic as compared to neutral stimulation elevated the regional to whole brain (relative) CBF in the secondary visual cortex but reduced relative rCBF in the hippocampus, prefrontal, orbitofrontal, temporopolar, and posterior cingulate cortex. Diazepam treatment did not affect the relative rCBF or the subjective or physiological fear indices. The observed rCBF pattern replicates our previous findings in snake phobics (M. Fredrikson et al. [1993] Psychophysiology, 30, 127-131; G. Wik et al. [1993] Psychiatry Research (Neuroimaging), 50, 15-24) and indicates that fear and anxiety affect cortical areas outside the classic limbic system areas.

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