Fear, stress, and anxiety present overlapping concepts. Anxiety disorders may involve normal anxiety pathways that are abnormally activated or failure of other brain areas to properly modulate anxiety pathways. In general, anxiety disorders show activation of the sympathetic nervous system and central noradrenergic systems while relatively normal functioning of the hypothalamic-pituitary-adrenal axis. The exception is PTSD, where significant controversy exists as to the HPA-axis picture with low cortisol, normal cortisol, and elevated cortisol reported in various studies. Despite controversy about basal cortisol, studies suggest exaggerated stress reactivity in PTSD as well as exaggerated amygdala response to fearful stimuli. Ultimately, neuroimaging studies in humans may help sort the various brain systems involved in fear, anxiety, and stress in both normal individuals and in individuals with anxiety disorders. 2009 Elsevier Inc. All rights reserved.
