Functional neuroimaging of the amygdala: the response to threatening and phobogenic stimuli]

Recent functional neuroimaging studies show that the amygdala has a central role in threat evaluation, in response to conditioned and unconditioned stimuli, in fear learning and fear extinction. The amygdala is involved in the pathophysiology of phobias and anxiety. In this review we critically examine the main findings of functional neuroimaging studies reporting data on the amygdala. Findings suggest that the response of the amygdala to threatening stimuli is mainly modulated by the infralimbic and prefrontal cortices, which inhibit activation of the amygdala (top-down inhibition), and by the hippocampus, the function of which is related to stimulus learning. The activity of the amygdala is modulated by various factors, like stimulus type and origin, emotion triggered by stimulus perception, and attention. The neural network comprising the amygdala and the frontal cortex is involved not only in top-down inhibition, but also in the emotional perception of facial expressions. This network also includes the thalamic pulvinar, which is densely interconnected with the amygdala, directly or indirectly, and which is activated by emotional face recognition of scary fear. Both top-down inhibition mechanisms and emotional face recognition are altered in anxiety disorders, particularly in specific and social phobia, resulting in reduced amygdalar activity inhibition after anxiety - or fear - inducing stimulus perception. Future functional neuroimaging studies will be able to provide new insights of normal and altered neurophysiology of the amygdala.