Fear Extinction Following Olfactory Targeted Memory Reactivation, a Future Treatment for PTSD?

    Post-traumatic stress disorder (PTSD) affects the lives of many Americans, especially those who have been subjected to domestic or war-related violence, as well as mass shooting events. With the rise of gun violence in the United States, rates of PTSD have the potential to rise as well, prompting a push for treatment options to be expanded. Exposure therapy has been historically utilized by clinicians to elicit fear extinction or suppression in individuals suffering from PTSD. Advances in virtual reality (VR) technology have provided clinicians with a treatment that can be highly specified to each individual's traumatic experience. However, immersion with VR is still limited as not all senses are being utilized. Most PTSD VR therapy employs the use of both auditory and visual stimuli in order to evoke the strongest emotional response possible (Josman et al. 2008). This increased immersion and emotional response are necessary to elicit the best results from exposure therapy but can be extremely unpleasant for subjects to re-experience such detailed traumatic events. 

    Until recently, there has been a gap in the literature regarding the possibility of conducting exposure therapy during sleep states which could reduce the unpleasant nature of such therapy. In Shanahan & Gottfried's work in 2017, they detail a study in which subjects were presented with two faces, one accompanied by an electrical shock and distinct odor, and another without a shock but with a distinct odor as well, while subjects undergo an fMRI (Hauner et al. 2013). Presentation of the shock-associated odorant during slow-wave sleep, followed by re-exposure to the conditioned stimulus (shock-associated face) during MRI scanning showed a marked decrease in both physical expressions of fear and activity of fear and memory-related brain regions, specifically the hippocampus, anterior cingulate cortex, and insula (Hauner et al. 2013). These results suggest that similar levels of fear extinction can occur during a sleep state as during wake states. Obviously, more research needs to be conducted in order to determine the efficacy of such treatment, but these findings suggest a potential for future therapies. 

References:

• BusWorld: An Analog Pilot Test of a Virtual Environment Designed to Treat Posttraumatic Stress Disorder Originating from a Terrorist Suicide Bomb Attack Naomi Josman, Ayelet Reisberg, Patrice L. Weiss, Azucena Garcia-Palacios, and Hunter G. Hoffman. CyberPsychology & Behavior 2008 11:6, 775-777
• Hauner KK, Howard JD, Zelano C, Gottfried JA (2013) Stimulus-specific enhancement of fear extinction during slow-wave sleep. Nat Neurosci 16:1553–1555