 It is thought that the locus coeruleus-noradrenergic system mediates the over-consolidation of fear memory.High levels of cortisol reduce noradrenergic activity, and because people with PTSD tend to have reduced levels of cortisol, it has been proposed that individuals with PTSD cannot regulate the increased noradrenergic response to traumatic stress.Intrusive memories and conditioned fear responses are thought to be a result of the response to associated triggers.