Research paperWhite matter microstructure of the uncinate fasciculus is associated with subthreshold posttraumatic stress disorder symptoms and fear potentiated startle during early extinction in recently deployed Service Members

- Greater understanding of factors that contribute to PTSD symptoms is needed.
- Subthreshold PTSD symptom severity associated with degraded white matter.
- Lower startle response during extinction was associated with elevated PTSD symptoms.
- Reveal vulnerabilities that could have significant implications for combat veterans.

Early intervention following combat deployment has the potential to prevent posttraumatic stress disorder (PTSD), but there is a need for greater understanding of the factors that contribute to PTSD symptom progression. This study investigated: (1) fear-potentiated startle during a fear extinction, (2) white matter microstructure, and (3) PTSD symptom severity, in 48 recently deployed service members (SMs) who did not have sufficient PTSD symptoms to meet criteria for a clinical diagnosis. Electromyography startle during a conditional discrimination paradigm, diffusion tensor imaging, and the Clinician Administered PTSD Scale were assessed in a cohort of SMs within 2 months after their return from Iraq or Afghanistan. Significant correlations were found between left uncinate fasciculus (UF) white matter tract integrity and total PTSD symptoms, r = −0.343, p = 0.018; the left UF and hyperarousal symptoms, r = −0.29, p = 0.047; right UF integrity and total PTSD symptoms r = −0.3371, p = 0.01; right UF integrity and hyperarousal symptoms r = −0.332, p = 0.023; left UF and startle during early extinction, r = .31, p = 0.033. Our results indicate that compromise of UF tract frontal-limbic connections are associated with greater PTSD symptom severity and lower startle response during extinction. In a subthreshold population, such a relationship between brain structure, physiological reactivity, and behavioral expression may reveal vulnerabilities that could have significant implications for PTSD symptom development.