Recent advances on the neurobiology of posttraumatic stress disorder include: the utilization of functional brain imaging; the incorporation of cross-system research including neuroendocrine (hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid axes), neurochemical (corticotropin-releasing factor, norepinephrine, serotonin, endogenous opiates), and neuroimmunological (humoral and c...