Many survivors of severe disasters, even those without posttraumatic stress disorder (PTSD), need psychological support. To understand the pathogenesis of PTSD symptoms and prevent the development of PTSD, the critical issue is to distinguish neurological abnormalities as vulnerability factors from acquired signs of PTSD symptoms in the early stage of adaptation to the trauma in the normal population. The neurological underpinnings of PTSD have been well characterized, but the causal relationships with the traumatic event are still unclear. We examined 42 non-PTSD subjects to find brain morphometric changes related to the severity of PTSD symptoms in a longitudinal magnetic resonance imaging study extending through the Great East Japan Earthquake. We found that regional grey matter volume (rGMV) in the right ventral anterior cingulate cortex (ACC) before the earthquake, and decreased rGMV in the left orbitofrontal cortex (OFC) through the earthquake were negatively associated with PTSD symptoms. Our results indicate that subjects with smaller GMV in the ACC before the earthquake, and subjects with decreased GMV in the OFC through the earthquake were likely to have PTSD symptoms. As the ACC is involved in processing of fear and anxiety, our results indicate that these processing are related to vulnerability for PTSD symptoms. In addition, decreased OFC volume was induced by failing to extinct conditioned fear soon after the traumatic event. These findings provide a better understanding of posttraumatic responses in early stage of adaptation to the trauma and may contribute to the development of effective methods to prevent PTSD.
The Great East Japan Earthquake, a severe magnitude 9.0 earthquake, hit Japan on 11 March 2011. The eastern half of Japan was severely affected, and the northeast coast suffered widespread destruction caused by a massive tsunami triggered by this earthquake. More than 15 000 people have been confirmed dead, and ∼4000 remain missing 6 months after the earthquake. Stress-related disorders such as acute stress disorder and posttraumatic stress disorder (PTSD) are likely to occur among the large number of survivors,1, 2, 3 but even those without PTSD will require psychological support.4 However, survivors without PTSD are likely to hesitate to ask for psychological supports and may not receive help, in contrast to those with PTSD. Distinguishing neurological abnormalities as a vulnerability factor from the acquired signs of PTSD symptoms in the early stage of adaptation to the trauma is essential both to understand the pathogenesis of PTSD and to prevent survivors from developing PTSD. Such information may provide a better understanding of posttraumatic responses and the development of effective methods to prevent PTSD.
The neurological underpinnings of PTSD have been well characterized, but the causal relationships to the traumatic event remain unclear, because of difficulties with prospective studies.5 Previous neuroimaging studies of patients with PTSD revealed morphological changes in several brain regions, including the hippocampus/parahippocampus,6 amygdala,6 anterior cingulate cortex (ACC),7, 8, 9 insula10 and orbitofrontal cortex (OFC),11, 12, 13 which were also found in healthy adults after stressful life events.14, 15 Evaluation of monozygotic twin pairs with combat-related PTSD has provided evidence that smaller hippocampal volume is a vulnerability factor for PTSD,16 and smaller pregenual ACC represents an acquired sign of PTSD.8 However, longitudinal structural changes as a vulnerability factor and an acquired sign of PTSD symptoms remain unclear. Some longitudinal studies have examined patients with PTSD after traumatic events, but failed to find subsequent brain structural changes.11, 17, 18 A recent longitudinal study revealed that decreased volumes in the ACC and hippocampus/parahippocampus were associated with the number of stressful life events, but the impacts of stress-related responses on brain structure were not examined.14 Therefore, the significance of longitudinal structural changes caused by posttraumatic response remained unclear.
This study tried to identify brain structural changes representing vulnerability factors and acquired signs of PTSD symptoms in non-PTSD survivors, based on a longitudinal study of structural magnetic resonance (MR) images obtained before and after the earthquake. In fact, we had obtained extensive structural MR imaging database from a group of healthy adolescents before the earthquake in multiple studies performed in our laboratory. Therefore, this extremely miserable episode provided a rare opportunity for investigating brain structural changes associated with such a disaster. We recruited 42 subjects from this group to examine structural MR images at 3–4 months after the earthquake. PTSD symptoms were also assessed using the Japanese version of the clinician-administered PTSD scale (CAPS) structural interview.19 We hypothesized that the vulnerability factors for PTSD could be detected by a significant association between the CAPS scores and smaller regional grey matter volume (rGMV) before the earthquake (Pre rGMV) in brain regions previously implicated in PTSD, and that the acquired signs could be detected by a significant association between the CAPS scores and decrease in rGMV from before to after the earthquake (Post-Pre rGMV). More specifically, based on previous monozygotic twin studies,8, 16 we could predict that smaller rGMV in the hippocampus would be identified as a pre-trauma vulnerability factor, and smaller rGMV in the ACC as an acquired sign of PTSD symptoms.
Materials and methods
Recruitment and selection of participants
Eligible participants were recruited from undergraduate and postgraduate students of the Tohoku University community, who met the eligibility criteria of having no history of neuropsychiatric disorders and right-handed dominance. All candidates had participated in past MR imaging experiments conducted in our laboratory, and had undergone structural MR imaging within 2 years before the earthquake, and had agreed to re-analyses of MR images obtained before the earthquake in advance. As all candidates lived around Sendai city, which was strongly affected by the earthquake, we did not plan to recruit control subjects unaffected by the earthquake. Neuropsychiatric disorders were screened using the mini international neuropsychiatric interview (M.I.N.I.).20, 21 Handedness was assessed by the Edinburgh Handedness Inventory.22 We were able to contact 42 of the numerous candidates in our database of past experiments. All candidates satisfied the eligibility criteria and provided written informed consents before participating in the current study to examine the possible effects of psychological trauma on brain structure, in accordance with the Declaration of Helsinki Principles.23 The M.I.N.I. confirmed that no subject had any history of psychiatric illness including PTSD, and no subjects were exposed to life-threatening experiences due to the earthquake and tsunami. This study and all previous studies were approved by the Ethics Committee of Tohoku University.
All participants were interviewed by trained psychologists (A Omoto, N Aikawa, N Saito, Y Watanabe and YK) using the CAPS structured interview.19, 24 In accordance with the M.I.N.I., no subject was diagnosed as having PTSD. Of the 42 participants, 8 subjects filled more than one, but not all, criteria of three clusters of PTSD symptoms, including re-experiencing of the event, avoidance and hyperarousal. In addition, the highest total CAPS score was 39, which is categorized as subthreshold PTSD.25 Therefore, we could regard all subjects as non-PTSD. The levels of anxiety and depression were evaluated using the state-trait anxiety inventory26, 27 and the Center for Epidemiologic Studies Depression Scale.28, 29 The diagnostic structured interview and MR imaging were conducted at 3–4 months after the earthquake. All psychological measurements were evaluated only after the earthquake.
All MR imaging data acquisition was conducted with a 3-T Philips Intera Achieva scanner (Best, Netherlands). By using a MPRAGE sequence, high-resolution T1-weighted structural images (240 × 240 matrix, repetition time=6.5 ms, echo time=3 ms, field of view=24 cm, 162 slices, 1.0-mm slice thickness) were collected.
Voxel-based morphometry analysis
To investigate the structural changes as vulnerability factors and acquired signs of PTSD symptoms in non-PTSD patients, voxel-based morphometry (VBM) was conducted. First, post-earthquake images were coregistered with pre-earthquake images in each subject on SPM2. Preprocessing of the morphological data was performed with VBM2 software,30 an extension of SPM2. Default parameter settings were used.30 In order to reduce the scanner-specific bias, a customized grey matter anatomical template was created from the pre-earthquake data of all participants in this study. Next, the T1-weighted structural images of each subject were segmented into grey and white matter partitions using the new grey and white matter prior probability maps. The resulting images included the extracted grey and white matter partitions in the native space. The grey matter partition was then normalized to the new grey matter probability map. The normalization parameters determined from this initial step were then applied to the native T1-weighted structural image. These normalized T1-weighted structural data were then segmented into grey and white matter partitions. The volumes of global grey matter, white matter and cerebrospinal fluid space were calculated using segmented and modulated images by adding a value derived from the voxel volume and multiplied by the value of each voxel. To facilitate optimal segmentation, normalization parameters were estimated with the previously reported protocol.31 In addition, a correction was performed for volume changes (modulation) by modulating each voxel with the Jacobian determinants derived from the spatial normalization, to test for regional differences in the absolute amount of grey matter.32 All images were subsequently smoothed by convolving with an isotropic Gaussian kernel of 8-mm full-width at half-maximum. Finally, the signal change in rGMV between pre- and post-earthquake images was calculated at each voxel for each participant. Only voxels that showed GMV values >0.10 in both pre- and post-earthquake images were included to avoid possible partial volume effects around the borders between grey matter and white matter, as well as between grey matter and cerebrospinal fluid. The resulting maps representing the rGMV before the earthquake (Pre rGMV) and the rGMV change between before and after the earthquake (Post-Pre rGMV) were then forwarded to the group-level analysis described below.
The group-level analysis tested for the relationship between individual severity of PTSD symptoms measured by the CAPS and rGMV. Voxel-by-voxel multiple regression analyses were performed using the CAPS scores for Pre rGMV and Post-Pre rGMV on SPM5. The analysis was performed with age, total brain volume, and periods between pre- and post-earthquake MR imaging data acquisition as additional covariates. Total brain volume was summation of segmented global grey matter and white matter volume in each subject. A significant level was set at P=0.05 corrected for multiple comparisons. Small volume correction33 was performed to examine each region of interest with a hypothesis (amygdala, hippocampus, insula, ACC and OFC)6, 7, 8, 9, 10, 11, 12, 13 using a lenient threshold of P=0.001, uncorrected as a cluster determined threshold, and a κ=100 to suppress the possibility of small clusters arising by chance, as used in previous neuroimaging studies.7 Small volume correction was applied to each region of interest using anatomical masks (amygdala, hippocampus, insula, ACC and OFC in each hemisphere) from the WFU_PickAtlas (http://fmri.wfubmc.edu/software/PickAtlas)34, 35 and the Anatomical Automatic Labelling Region of Interest package,36 as used in previous VBM studies of PTSD,7, 8, 37, 38 as well as functional MR imaging studies.39, 40 Finally, to verify the effect of the structural changes on the CAPS scores, regression analysis was performed using Pre rGMV and Post-Pre rGMV at peak voxels in each cluster as explanatory variables, and total scores of CAPS as independent variables.
Demographic characteristics of the subjects are shown in Table 1. The distribution of the CAPS scores is illustrated in Figure 1. After controlling for age, total brain volume, and periods between pre- and post-earthquake MR imaging data acquisition, the total scores of CAPS were significantly associated with smaller Pre rGMV in the right ventral ACC (x=6, y=32, z=0; Figure 2a, Table 2), and decreased Post-Pre rGMV in the left OFC (x=−20, y=52, z=−6; Figure 2b, Table 2), based on region of interest analysis. Post hoc regression analysis revealed that Pre rGMV in the right ventral ACC and Post-Pre rGMV in the left OFC accounted for 48% score variance in the CAPS (F(2, 39)=18.28, R2=0.48, P<0.001; Figure 3).
The aim of this study was to investigate the brain structural changes as vulnerability factors and acquired signs of PTSD symptoms in non-PTSD survivors. We found the total scores of CAPS were negatively associated with Pre rGMV in the right ventral ACC, and negatively associated with Post-Pre rGMV in the left OFC.
According to our hypothesis, smaller Pre rGMV in the right ventral ACC and decreased Post-Pre rGMV in the left OFC are structural changes representing vulnerability factor and acquired sign of PTSD symptoms, respectively. Additionally, these structural changes could explain approximately half of the observed PTSD symptoms.
Our longitudinal study provides further evidence of the causal relationships between brain structural changes and posttraumatic responses. Previous longitudinal studies have investigated brain structural changes only after the traumatic events,11, 17, 18 but failed to find any brain volume reduction in patients with PTSD. Another longitudinal study revealed that the number of stressful life events is associated with decreased volumes in the ACC and hippocampus/parahippocampus in healthy subjects, but the causal relationship between psychological responses to the stressful events and brain structural changes was not examined.14 On the other hand, in contrast to our findings, investigations of monozygotic twin pairs with PTSD revealed smaller hippocampal volume as a vulnerability factor,16 and smaller pregenual ACC as an acquired sign of PTSD.8 We suppose that these discrepant findings result from fundamental differences in study designs. Monozygotic twin studies cannot distinguish acquired signs of PTSD from acquired signs from birth to trauma, because of the cross-sectional design only after the traumatic events.8 On the basis of our present findings, smaller ACC volume is not an acquired sign, but an acquired vulnerability of PTSD before exposure to traumatic events, which could have been identified as an acquired sign of PTSD in the monozygotic twin study.8
Several lines of evidence support the notion that smaller ventral ACC volume is a vulnerability factor for PTSD symptoms. An essential role of the ventral ACC is the processing of anxiety and fears,41 which is supposed to be highly related to the manifestation of the clinical symptoms of PTSD.42 In fact, smaller ACC volume is one of the more robust VBM findings in patients with PTSD,7, 8, 9 also in normal subjects after stressful life events.14, 15 Whether such a smaller volume in the ventral ACC represents an acquired abnormality or a pretrauma vulnerability factor for PTSD is still under discussion.8 Our present findings provide evidence that smaller ventral ACC volume is a pretrauma vulnerability factor for PTSD.
rGMV in the ACC is associated with personality traits related to PTSD symptoms. Harm avoidance,43 which is predictive of increased PTSD symptom severity,44 is positively associated with anatomical variability of the ACC.45 Individuals with alexithymia, which is positively associated with PTSD symptoms,46 had smaller ACC volume.47 Combined with our findings, these observations support the possibility that these psychological characteristics are also vulnerability factors for PTSD.
The cognitive functions of the OFC indicate posttraumatic responses of the survivors soon after the earthquake. A principal function of the OFC is associated with extinction of conditioned fear. Previous lesion studies revealed that OFC lesion caused resistance to the extinction of conditioned fear in both non-human primates48 and human patients with OFC lesions.49 Neural responses in the OFC were preferentially enhanced with those in the amygdala during extinction,50 and this relationship is crucial in the voluntary regulation of emotions.51, 52 In particular, the left lateral part of the OFC is involved in emotional distraction. The left OFC is also involved in suppression of emotional distracters during working memory performance.53 In fact, patients with PTSD had less activity in the OFC than normal control subjects during extinction to conditioned fear54 and emotion regulation.55 Given the previous findings, our results indicate that decreased OFC volume might reflect difficulty in distracting emotional memories of experiences related to the earthquake. Therefore, survivors with high CAPS scores are likely to have more difficulty in distracting emotional memories compared with those with low CAPS scores.
Some limitations should be considered when interpreting the present results. First, our study included no subjects with supra-threshold PTSD symptoms and no control group without experience of the earthquake. These were predetermined limitations of this study, because most of the candidates in our pre-earthquake database were supposed to have been affected by the earthquake to some extent, but not exposed to life-threatening experiences. We believe that the investigation of subjects with subclinical PTSD symptoms can provide sufficient evidence, like previous studies.14, 15, 56, 57, 58, 59 However, a further longitudinal study of patients with supra-threshold PTSD symptoms caused by traumatic events is necessary to examine whether the brain structural changes in our current investigation is applicable to such individuals.
Second, the CAPS scores were not normally distributed across subjects (Figure 1). As this distribution may be consistent with the expected distribution in the normal population, investigating such a population was inevitable. Even if multiple regression analysis on SPM allows independent values of non-normal distribution, the distorted distribution of the CAPS score may reduce the statistical power. Actually, of the 42 participants, 37 scored 0 to 19 and 5 scored 20 to 39 in the CAPS, which are categorized as asymptomatic and subthreshold PTSD, respectively.25 By applying these two categories to group comparison analysis (that is, two sample t-test) as non-PTSD and subclinical PTSD groups, respectively, we found that similar brain regions including the Pre rGMV in the right ventral ACC and the Post-Pre rGMV in the left OFC were negatively associated with the CAPS scores (P<0.05, small volume correction in each region of interest). However, another problem is that the sample size for subjects with subthreshold PTSD was too small to perform group comparison. We could not exclude the possibility that regions other than the ACC and OFC may show significant association with the CAPS scores, if the sample size was improved.
Third, although all subjects were diagnosed as normal, it was suspected that the anxiety level of subjects was relatively high. We supposed that such high anxiety level might be caused by the aftermath of the earthquake, such as frequent afterquakes and dispersed radioactive material leaking from the nuclear plants.60 The high anxiety levels may have some effects on the MR imaging findings. However, even if we adjusted both state and trait anxiety scores as additional covariates, we showed that similar brain regions, including the Pre rGMV in the right ventral ACC and the Post-Pre rGMV in the left OFC, were negatively associated with total CAPS scores (P<0.001, uncorrected). Therefore, our MR imaging findings were robust despite the high anxiety level.
Fourth, numerous studies revealed smaller rGMV associated with PTSD in the amygdala and hippocampus,6 and also smaller hippocampal volume represented vulnerability factor for PTSD,16 but we failed to detect these brain regions either as a vulnerability factor or an acquired sign of PTSD. VBM may not detect such small and localized GMV reduction, because false-positive or false-negative VBM findings may arise from the change of spatial normalization.7, 61 Actually, when applying more lenient thresholds (P<0.01, uncorrected) to this study, we could find negative associations between the CAPS scores and both Pre rGMV and Post-Pre rGMV in the hippocampus.
Despite these limitations, the present longitudinal study could distinguish structural changes representing a vulnerability factor from structural changes representing an acquired sign of PTSD symptoms in the early stage of adaptation to trauma. These findings may be essential to discriminate between survivors with and without PTSD symptoms soon after a traumatic event, and between survivors who will and will not develop PTSD, even in the normal population. These findings provide a better understanding of the posttraumatic responses in the early stage of adaptation to trauma, and may contribute to the development of effective methods to prevent PTSD in the normal population.
We thank the study participants and all of our colleagues in the Institute of Development, Aging, and Cancer and in Tohoku University for their support. We also thank A Omoto, N Aikawa, N Saito and Y Watanabe for conducting the CAPS structured interview. AS was supported by a Grant-in-Aid for Young Scientists (B) (KAKENHI 22790611, 24790653) from the Ministry of Education, Culture, Sports, Science and Technology, and Grants-in-Aid for Scientific Research from the Ministry of Health, Labour and Welfare in Japan from the Ministry of Education, Culture, Sports, Science and Technology in Japan.