 Dominant theories in the field of PTSD emphasize a key role for threat-related learning and memory processes in the underlying etiology and maintenance of PTSD symptoms, such as absent or insufficient extinction of learned fear associations. Indeed, trauma-focused therapy protocols typically involve repeated imaginal or in vivo recall of traumatic memories in a systematic, controlled manner, while employing anxiety-reducing techniques, and without experiencing additional external trauma. Thus, these therapies parallel cue-extinction training within a model of learning and unlearning of conditioned responses, with the patients diminished fear response over successive extinction trials reflecting the weakening of trauma-induced associations between the fear-provoking stimuli and the conditioned fear response. Extinction of fear responses is thus generally assumed to be one the most important underlying mechanisms of exposure therapy. Noting the limited efficacy of trauma-focused treatment and in particular the spontaneous relapse, there is much room for improving the effectiveness of this cue-extinction process in a manner that is not dangerous to the patient cf. extinction-enhancing pharmacological agents that are also toxic. 