A FUNCTIONAL CEREBRAL RESPONSE TO FRIGHTENING VISUAL-STIMULATION

The defense reaction, a fundamental reflex in the human behavioral res ponse to threat, is characterized by anxiety and increased activity of the sympathetic nervous system. To study changes in regional cerebral blood flow (rCBF) related to the defense reaction, volunteers with sn ake phobia were investigated with positron emission tomography. The re lative rCBF during phobogenic visual stimulation was increased in the secondary visual cortex but reduced in the hippocampus, orbitofrontal, prefrontal, temporopolar, and posterior cingulate cortex compared wit h that observed during neutral visual stimulation. The relative rCBF u nder aversive stimulation was intermediate between phobic and neutral stimulation. The rCBF patterns observed are suggested to represent a f unctional cerebral correlate to the visually elicited defense reaction and its associated emotions.