QUOTE(alexryan @ Jun 23, 2010, 05:02 PM)
I have read some conflicting information about how regulation of fear is achieved... One source claimed that the Anterior Cingulate Cortex was responsible for calming the amygdala. Another claimed that it was the Neo-cortex.
I'm not sure it is really known how fear regulation (or any type of emotional regulation) is achieved.
Emotions seems to be the result of a complex web of signaling activity and dynamic processes involving a large number of brain areas.
It is often said that the amygdala is responsible for fear, and it does seem to have a prominent role in centrally organizing fear responses. However extreme fear reactions can be triggered by stimulating certain nuclei in the brain stem as well, for example. Also, the Amydala is involved in a lot of things, including certain aspects of memory (good/bad valance tagging), reward processing, desire, motivation, attention.
As far as what part of the brain "regulates" the amygdala, that is not clear either. The Amygdala gets input from a large number of brain areas, including many cortical areas. The anterior cingulate cortex (ACC) and prefrontal cortex (PFC) figure prominently, although ironically, these project to the part of the amygdala involved in sensory processing (the BLA), rather than the part most involved in emotional responses (the central nucleus). But the two are connected.
A quick search on Google Scholar turns up papers discussing roles for the following areas in emotional regulation of the amygdala: ventromedial PFC, dorsomedial PFC, lateral and dorsal PFC, orbitofrontal cortex (OFC), anterior cingulate cortex (ACC).
"amygdala hijack" is a phrase that has appeared recently in pop-psychology to describe situations in which strong emotions take over control of behavior and supress more reasoned, goal-oriented influences, presumeably coming from the prefrontal cortex. However this concept seems to be a metaphor for coaching people on emotion management that is inspired by neuroscience but is not an actual neuroscience theory.
What seems likely is that emotions, including fear, are complex homeostatic systems involving a dynamic exchange and synthesis of signals across dozens of brain areas. It seems unlikely that any one part of the brain has a regulating role, although there are probably certain areas, for example prefrontal regions, that have a greater ability than others to influence, inhibit or alter emotional responses such as fear to align them with cognitively-derived goals.