The amygdala

The amygdala is a central structure of the limbic system of the brain that is involved in producing appropriate emotional responses. Each emotion is produced by a different set of nerve modules in the brain. Two other brain structures are involved in these modules, namely the hypothalamus and the pituitary gland. It is these two structures that control the hormones that produce physical reactions associated with particular emotions. The hypothalamus in particular modulates the activation of the amygdala. It is the amygdala that instantly assesses incoming information and determines the appropriate emotional response. On determining the appropriate response it sends signals to other brain structures to carry out suitable action; typically signals to the hypothalamus that triggers hormonal changes that alter muscle contraction and influence the heart rate. All this is an unconscious process. This, however, is only one of the routes in the brain responding to fear. This unconscious path is referred to as the ‘low road’. The second route to the amygdala arising from an emotional stimulus goes via the cortex where it is consciously evaluated. This slower conscious route is referred to as the ‘high road’. These two routes are shown in the following figure.