Data informing this report was collected between 2015 and 2020 as part of the NIMH-funded ‘Neurobehavioral Moderators of Post-traumatic Disease Trajectories’ study (MH103287). This research project was approved by the Tel-Aviv Sourasky Medical Center institutional review board (approval 0207/14) and was registered on ClinicalTrials.gov (NCT03756545). The study’s design and detailed methodologies have been previously published30 and those informing this work are summarized below.
Participants. Potential participants for this study were 18 to 65 years old adult civilians consecutively admitted to Tel-Aviv Sourasky Medical Center (TASMC) emergency department (ED) after one of the following events: motor-vehicle accident (MVA), bicycle accident, physical assault, robbery, hostilities, electric shock, fire, drowning, work accident, terror attack or a large-scale disaster.
Participants were included in the study if they met PTSD symptom criteria (specified below) within one month following trauma exposure (T1). Participants were excluded if they had an ED notation of severe head injury, coma upon ED admission, a medical condition that interfered with their ability to provide informed consent or apprehend the study’s procedures, a diagnosis of PTSD prior to ED admission, current substance abuse disorder, current suicidal ideations, lifetime psychotic illness, conditions precluding MRI scanning (e.g., pacemaker, metal implants, large tattoos, permanent makeup) or medical/ psychological conditions that constituted treatment priority. All participants in this study provided oral consent to the study’s screening telephone interview and written informed consent upon attending a subsequent diagnostic and eligibility ascertainment clinical interview.
A final sample of n = 100 participants with valid clinical and structural brain data (at T1, T2, and T3) are included in the current report (i.e., ‘study completers’). While all participants (n = 100) met PTSD diagnostic criteria at T1, only n = 29 still met PTSD diagnosis at T3 (a ‘non-Remission’ Group), while n = 71 did not (a ‘Remission’ Group). For a comparison of demographic and clinical characteristics of the study groups (‘Remission’ vs. ‘non-Remission’), see Table 1.
Table 1. Participants’ demographic and clinical characteristics. While all participants met PTSD diagnostic criteria at 1-month post-trauma (T1), 29 individuals met PTSD diagnostic criteria at 14-months post-trauma (T3) (‘non-Remission’ Group) and n=71 did not (‘Remission’ Group). MVA=Motor Vehicle Accident; CAPS= Clinical-Administered PTSD Scale.
Clinical Assessments. A comprehensive clinical interview was conducted by trained clinicians, using the Clinician-Administered PTSD Scale (CAPS), to assess PTSD diagnosis and severity estimates at 1-, 6-, and 14-months after ED admission (T1, T2, and T3, respectively). In order to maintain continuity with decades of PTSD research based on DSM-IV definitions, and given the findings of nonoverlapping samples per definitional criteria used31,32, we administered a combined clinical interview assessing both CAPS-IV33 and CAPS-534 items at the same time. The usage of such hybrid PTSD diagnostic interviews is supported, particularly in longitudinal studies35, and is in line with the recommendation to use broader cross-template definitions of PTSD for empirical research36. Here, a positive PTSD diagnosis was given to individuals who met either DSM-IV or DSM-5 diagnostic criteria or, in line with previous recommendations37 endorsed CAPS-IV total score of ≥ 40.
MRI Acquisition. Whole-brain anatomical images were conducted using a 3T MAGNETOM Prisma system (Siemens Medical Solutions, Erlangen, Germany) at the Tel-Aviv Sourasky Medical Center (TASMC). These repeated structural MRI scans took place at three different time points following traumatic exposure (T1, T2, and T3). At each time point, a sagittal T1-weighted magnetization prepared rapid gradient echo (MPRAGE) sequence (TR/TE = 2400/2.29ms, flip angle = 8°, voxel size = 0.7mm3, field of view = 224×224mm2, slice thickness = 0.7mm) was used to acquire high-resolution structural images. Foam padding and earplugs were used to reduce head motion and scanner noise.
Hippocampus and Amygdala Segmentations. Hippocampal and amygdala segmentations were performed on structural T1-weighted images (voxel size = 0.7mm3) using the longitudinal pipeline38 of FreeSurfer image analysis suite39 version 7.1.0. This longitudinal pipeline reduces the confounding effect of inter-individual variability, thus increasing the robustness of the method and yielding more sensitive brain volumes40. It further increases the reliability and statistical power by using an unbiased within-subject template space38 (based on all available time-points of a subject), and allowed us to use all available data (i.e., also when one time-point out of three was missing).
Segmentations of hippocampus and amygdala subregions were obtained using a special-purpose module included in FreeSurfer version 7.1.0, an evolution of the previous hippocampal subfields’ module released with FreeSurfer 6.0. This tool uses a probabilistic atlas built with ultra-high resolution ex-vivo MRI data (~ 0.1mm isotropic) to produce an automated segmentation of the hippocampal substructures41 and the nuclei of the amygdala42. Using this processing pipeline, hippocampal subfields and amygdala subnuclei were segmented simultaneously, ensuring that these two structures do not overlap or leave gaps in between40–42. Overall, this analysis provides volumes of 12 bilateral hippocampal subfields (subdivided in body and head when applicable) and volumes of 9 bilateral amygdala subnuclei.
For each participant, at each time point (T1, T2, T3), volumes of the left and right amygdala and hippocampus were derived, as well as its intracranial volume (ICV). These measures were previously shown to have good agreement with manual volumetric assessment and other automatic methods43–46. Furthermore, we extracted volumes of specific subregions within the right and left hippocampus previously implicated in PTSD literature26,47−49, namely the Cornu Ammonis 1 and 3 (CA1 and CA3), the dentate gyrus (DG), and the subiculum (see Fig. 1a). Importantly, these subregions also showed excellent reliability between two consecutive days approximately 2-weeks after their traumatic injuries29. Similarly, we extracted volumes of specific subregions within the right and left amygdala previously implicated in PTSD literature50–52, namely the lateral, central, and basal nuclei (LA, CeA, and BA, respectively; see Fig. 1b). For more details regarding the a-priori selected subregions, see Supplementary Methods. Finally, all hippocampus and amygdala segmentations were visually inspected and checked according to standardized quality control procedures26 (see Supplementary Methods & Fig. S1).
Procedure.
The hospital’s ED computerized records were available to the study team within 24 hours of ED admission. Within these records, an ED ‘trauma’ notation generated initial screening contacts from 3 days after the ED admission.
Initial telephone screening was performed by trained study personnel within 10–14 days of ED admission, and only after individuals were discharged from the hospital. After explaining the purpose of the call and obtaining verbal consent, interviewers confirmed the occurrence of a psychologically traumatic event and associated distress, availability for the study, and salient exclusion criteria (i.e., a 5–10 minutes ‘short interview’). Next, interviewers evaluated PTSD symptom severity using a modified dichotomous version of the PTSD checklist IV for civilians (PCL)30,53, study availability, and full exclusion criteria (i.e., a 20–30 minutes ‘long interview’). Participants who met PTSD diagnostic criteria (except for the 1-month duration), and did not meet any of the exclusion criteria, received further verbal information about the study and were invited for a first clinical assessment.
Clinical interviews took place within 1-month (23.9 ± 8.2 days) after ED admission at our lab. After signing informed consent, trained clinicians from the study team assessed PTSD diagnosis and severity using the CAPS (see ‘Clinical Assessments’). Additionally, the interviewers re-assessed (in-person) the presence of previously unnoticed study exclusion criteria. Identical follow-up clinical interviews took place at 6- and 14-months post-trauma (T2 and T3).
MRI Scans for eligible participants took place around 1-month (30.4 ± 9.5 days) after ED admission at our lab (after the clinical interview). Several participants were excluded at this stage since they were not eligible for MRI scans (e.g., pacemakers, non MRI-compatible implants, permanent make-up, large tattoos). Identical follow-up scans took place at T2 and T3.
Statistical Analysis. The study’s primary outcome measures were right and left hippocampus and amygdala volumes (mm3) at T1, T2, and T3. Secondary outcome measures were volumes (mm3) of specific subregions within the hippocampus (CA1, CA3, DG, and subiculum) and within the amygdala (LA, CeA, and BA nuclei). Differences in both primary and secondary outcome measures were measured between the two study groups (Remission vs. non-Remission; see Participants) both at T1 and across all time points (T1, T2, and T3).
Bayesian Multilevel Modeling (BML) Analysis. Inspired by the recent work of Limbachia et al. (2021)54, we leveraged the strengths of Bayesian multilevel modeling (BML)55–57 to estimate volumetric changes over time and initial differences between the two study groups (Remission vs. non-Remission). One of the strengths of BML is that it allows the simultaneous estimation of multiple parameters within a single model, hence there is no need to apply a correction for multiple comparisons58. In this study, we used a single model to assess initial volumetric differences (at T1) between the study groups (Remission vs. non-Remission; main effect of Group) across all regions of interest (ROIs): left and right amygdala and hippocampus, as well as their subregions simultaneously (see ‘Hippocampus and Amygdala Segmentations’). A second model was used to test whether there are volumetric changes across time (T1 to T2 to T3), across all individuals (main effect of Time) or between study groups (Group-by-Time interaction) across all ROIs. Both models included covariates of participants’ age and gender. To account for differences in brain sizes, we included total intracranial volume (ICV) and whole hippocampus/amygdala as additional covariates. Both models included the Remission group as the baseline, a random slope for each ROI, and Subjects as a random intercept. Model specifications also included 40K iterations, a 99% acceptance rate (i.e., adaptive delta), and a maximum tree depth of 15. We report evidence in terms of P+, the probability of the presence of an effect of interest, based on the posterior distribution (ranging from 0 to 1)54. While values closer to P + = 1 provide evidence that the effect of interest is greater than zero (e.g., increased volume in non-Remission vs. Remission group), values closer to P + = 0 convey support for a reverse effect (e.g., increased volumes in the non-Remission vs. Remission group). As values are closer to P + = 0.5, they provide stronger evidence for no-effect (e.g., similar volumes between groups). We treat Bayesian probability values as providing a continuous amount of support for a given hypothesis (not dichotomously as in “significant” vs. “not significant”). Nevertheless, in line with previous work54, we used cut-off points of P + > 0.85 and P + < 0.15 as evidence for differences between the groups.