Positron tomographic emission study of olfactory induced emotional recall in veterans with and without combat-related posttraumatic stress disorder

Abstract

Objective: Memory for odors is often associated with highly emotional experiences, and odors have long been noted by clinicians to be precipitants of trauma symptoms in posttraumatic stress disorder (PTSD). Primitive brain systems involved in fear responsivity and survival also mediate smell, including the olfactory cortex and amygdala. The purpose of this study was to measure neural correlates of olfaction in PTSD.

Methods: We exposed male combat veterans with PTSD (N = 8) and without PTSD (N = 8) to a set of smells, including diesel (related to traumatic memories of combat), and three other types of smells: odorless air, vanilla/coconut, and hydrogen sulfide (H2S) (respectively, a neutral, positive, and negative hedonic nontraumatic smell) in conjunction with PET imaging of cerebral blood flow and assessment of psychophysiological and behavioral symptoms. All subjects also underwent a baseline of olfactory acuity.

Results: PTSD patients rated diesel as unpleasant and distressing, resulting in increased PTSD symptoms and anxiety in PTSD versus combat controls. Exposure to diesel resulted in an increase in regional blood flow (rCBF) in amygdala, insula, medial prefrontal cortex, and anterior cingulate cortex, and decreased rCBF in lateral prefrontal cortex in PTSD in comparison to combat controls. Combat controls showed less rCBF changes on any smell, and did not show amygdala activation upon diesel exposure.

Conclusions: These data support the hypothesis that in PTSD trauma-related smells can serve as strong emotional reminders. The findings indicate the involvement of a neural circuitry that shares olfactory elements and memory processing regions when exposed to trauma-related stimuli.

Figure 1

Salivary Cortisol during the PET olfaction experiment in combat-related PTSD and combat controls.

Figure 2

Areas of increased blood flow in diesel and PTSD patients (top row) and combat controls (bottom row) in different horizontal sections through the brain (slice 31 and 32: z= −12; slice 44 and 45: z=6; slice 49 and 50: z=26). Brain sections were chosen to illustrate the relevant activations. Between brackets are Brodman areas. PAG= periaquaductal grey. (Z Score >3.09, p<0.001)

Figure 3

Areas of greater increases (left column) and greater decreases (right column) in blood flow in vanilla (top), diesel (middle) and hydrogen sulfide (bottom) in PTSD compared to combat controls (z=0 and z=14). Brain sections were chosen to illustrate the relevant activations. Precise locations of the peaks for the activity shown are given in the corresponding table (Table 5). Between brackets are Brodman areas. nc=nucleus caudatus (Z Score >3.09, p<0.001)