Basic science research on memory consolidation and fear conditioning has demonstrated that heightened adrenergic activation can promote the consolidation and retrieval of fear-provoking memories (Bohus and Lissak 1968). Building on this preclinical work, conditioning models of trauma response propose that PTSD is the result of strong associative learning whereby individuals initially react to a traumatic event (unconditioned stimulus) with arousal and fear (unconditioned response). Individuals with PTSD then continue to show arousal (conditioned response) when confronted with trauma-related cues (conditioned stimuli). It has been hypothesized that terror-driven sympathetic arousal at the time of a traumatic event may result in the release of stress-related neurochemicals (including norepinephrine and epinephrine) in the cortex, mediating an overconsolidation of trauma memories (Pitman 1989).