Cortical complexity in world trade center responders with chronic posttraumatic stress disorder

Abstract

Approximately 23% of World Trade Center (WTC) responders are experiencing chronic posttraumatic stress disorder (PTSD) associated with their exposures at the WTC following the terrorist attacks of 9/11/2001, which has been demonstrated to be a risk factor for cognitive impairment raising concerns regarding their brain health. Cortical complexity, as measured by analyzing Fractal Dimension (FD) from T₁ MRI brain images, has been reported to be reduced in a variety of psychiatric and neurological conditions. In this report, we hypothesized that FD would be also reduced in a case-control sample of 99 WTC responders as a result of WTC-related PTSD. The results of our surface-based morphometry cluster analysis found alterations in vertex clusters of complexity in WTC responders with PTSD, with marked reductions in regions within the frontal, parietal, and temporal cortices, in addition to whole-brain absolute bilateral and unilateral complexity. Furthermore, region of interest analysis identified that the magnitude of changes in regional FD severity was associated with increased PTSD symptoms (reexperiencing, avoidance, hyperarousal, negative affect) severity. This study confirms prior findings on FD and psychiatric disorders and extends our understanding of FD associations with posttraumatic symptom severity. The complex and traumatic experiences that led to WTC-related PTSD were associated with reductions in cortical complexity. Future work is needed to determine whether reduced cortical complexity arose prior to, or concurrently with, onset of PTSD.

Fig. 1. Group-wise nonparametric analyses of FD using surface-based morphometry comparing PTSD negative to PTSD positive responders.

Regions lacking significant differences in FD between groups are shown in gray while statistically significant results are shown using a rainbow colormap ranging from blue to red. Figure generated using Computational Anatomy Toolbox (CAT12) with superimposed Desikan–Killiany (DK) atlas regions shown in black borders.

Fig. 2. Raincloud plots showing data distribution (cloud), jittered raw data and central tendency boxplots comparing absolute cortical complexity between WTC responders with PTSD versus those without.

Analyses identified significantly lower absolute whole brain cortical complexity (Welch’s t = −3.3144, p = 0.0013, Cohen’s d = −0.67) in the PTSD + group (mean = 2.5946, SD = 0.0234), when compared to the PTSD- group (mean = 2.6107, SD = 0.0247). PTSD posttraumatic stress disorder, X-axis denotes whole brain FD.

Fig. 3. Raincloud plots showing pairwise comparisons between bilateral cortical complexity between WTC responders with PTSD versus those without.

Analyses identified lower absolute cortical complexity in the PTSD + group in the left hemisphere (t = −2.5535, p = 0.0122, Cohen’s d = −0.5139; PTSD+: mean = 2.5979, SD = 0.0290; PTSD−: mean = 2.6128, SD = 0.0289), and the right hemisphere (t = −3.1798, p = 0.0020, Cohen’s d = −0.6358; PTSD + : mean = 2.5913, SD = 0.0257; PTSD−: mean = 2.6085, SD = 0.0282), when compared to the PTSD- group. PTSD posttraumatic stress disorder, X-axis denotes hemispheric FD.