Imaging fear and anxiety in the human brain : Positron emission tomographic studies

Abstract: Fear and anxiety are central human experiences. However, the relation between aspects of these aversive emotional states and brain function have previously been studied mostly in animals. To investigate human brain function during normal fear and anxiety, the present thesis employed positron emission tomography methodology in conjunction with activation and symptom provocation paradigms. Classical fear conditioning (i.e., the acquired ability of a neutral stimulus to induce stress after pairings with an aversive stimulus), trauma re-experience and panic anxiety were investigated.During the memory formation phase of fear conditioning, regional cerebral blood flow (rCBF), which is an index of neural activity, increased in the right prefrontal gyrus and decreased bilaterally in the superior temporal gyrus and the left hippocampus. After fear conditioning during the memory expression phase, increases in rCBF were evident bilaterally in the hypothalamus, the thalamus, the central grey of the midbrain, the cerebellum, the anterior cingulate cortex and in the left striatum and right prefrontal cortex, whereas rCBF decreased bilaterally in the amygdala, the prefrontal, temporal, parietal and occipital cortices. Hence, fear-related memory formation and expression involve both overlapping and unique cortical networks.In contrast to a neutral state, rCBF increased during an anxiety episode resulting from trauma re-experience in the left orbitofrontal cortex and bilaterally in the posterior cingulate and occipital cortices. Decreased rCBF was found in Brocas' area and in the left operculum, angular gyrus and secondary somatosensory cortex. During unexpected panic resulting from electric shock stimulation, as opposed to electric shocks without panic, rCBF decreased in the right orbitofrontal, prelimbic, anterior cingulate and temporal cortices.In accordance with numerous brain imaging studies, the present papers implicate anterior paralimbic and prefrontal structures in the functional neuroanatomy of symptomatic fear and anxiety.

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