Positron tomographic emission study of olfactory induced emotional recall in veterans with and without combat-related posttraumatic stress disorder.
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.
Vermetten
Eric
E
University Medical Center, Utrecht, The Netherlands. e.vermetten@umcutrecht.nl
Schmahl
Christian
C
Southwick
Steven M
SM
Bremner
J Douglas
JD
D000328:Adult; D000679:Amygdala / Q000098:blood supply / Q000000981:diagnostic imaging; D001921:Brain / Q000098:blood supply / Q000000981:diagnostic imaging*; D001931:Brain Mapping; D003130:Combat Disorders / Q000000981:diagnostic imaging*; D004644:Emotions / Q000502:physiology*; D006801:Humans; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D008875:Middle Aged; D009833:Olfactory Pathways / Q000098:blood supply / Q000000981:diagnostic imaging; D049268:Positron-Emission Tomography; D012039:Regional Blood Flow / Q000502:physiology; D012903:Smell / Q000502:physiology*; D014728:Veterans / Q000523:psychology*