Bedtime regularity predicts positive affect among veterans with posttraumatic stress disorder: an ecological momentary assessment study.

BACKGROUND: Regularizing bedtime and out-of-bed times is a core component of behavioral treatments for sleep disturbances common among patients with posttraumatic stress disorder (PTSD). Although improvements in subjective sleep complaints often accompany improvements in PTSD symptoms, the underlying mechanism for this relationship remains unclear. Given that night-to-night sleep variability is a predictor of physical and mental well-being, the present study sought to evaluate the effects of bedtime and out-of-bed time variability on daytime affect and explore the optimal window lengths of over which variability is calculated. METHODS: For about 30 days, male U.S. military veterans with PTSD (N = 64) in a residential treatment program provided ecological momentary assessment data on their affect and slept on beds equipped with mattress actigraphy. We computed bedtime and out-of-bed time variability indices with varying windows of days. We then constructed multilevel models to account for the nested structure of our data and evaluate the impact of bedtime and out-of-bed time variability on daytime affect. RESULTS: More regular bedtime across 6-9 days was associated with greater subsequent positive affect. No similar effects were observed between out-of-bed time variability and affect. CONCLUSIONS: Multiple facets of sleep have been shown to differently predict daily affect, and bedtime regularity might represent one of such indices associated with positive, but not negative, affect. A better understanding of such differential effects of facets of sleep on affect will help further elucidate the complex and intertwined relationship between sleep and psychopathology. TRIAL REGISTRATION: The trial retrospectively was registered on the Defense Technical Information Center website: Award # W81XWH-15-2-0005.

Neighborhood disadvantage is associated with sleep disturbance in a sample of trauma-exposed Veterans.

OBJECTIVES: This study examined associations among neighborhood disadvantage, all-night respiratory sinus arrhythmia, fear of sleep, nightmare frequency, and sleep duration in a sample of trauma-exposed Veterans. METHODS: Participants completed baseline assessments and slept on a mattress actigraphy system for seven nights. Neighborhood disadvantage was assessed with the Area Deprivation Index, a census-based socioeconomic index. Differences between the least and most disadvantaged groups on the sleep variables were analyzed. RESULTS: Data were available from 37 Veterans. Residing in neighborhoods with greater disadvantage was associated with elevated fear of sleep and reduced sleep-period respiratory sinus arrhythmia. No significant differences were observed for nightmare frequency or sleep duration. A regression confirmed that neighborhood context had a significant effect on respiratory sinus arrhythmia, after controlling for other baseline sleep variables. CONCLUSIONS: In this sample of Veterans, sleep context may increase hypervigilance in turn serving as a mechanism by which trauma-induced sleep disruptions are maintained.

Dog ownership may promote cardiometabolic health in U.S. military veterans.

Dog ownership has been associated with reduced cardiovascular and all-cause mortality in civilian epidemiological samples. Associations between dog ownership and cardiometabolic disease were examined in the 2019-2020 wave of the National Health and Resilience in Veterans Study. Dog and cat ownership data were obtained from 3078 Veterans and cross-tabulated with self-reported, professionally diagnosed, heart disease, heart attack, stroke, high blood pressure, diabetes, and high cholesterol. In unadjusted tests, dog ownership was associated with lower rates of heart disease, high blood pressure, diabetes, and high cholesterol, while cat ownership was not. Relative to non-owners, dog owners were younger, were more likely to screen positive for posttraumatic stress disorder and/or major depressive disorder, and more active. Binary logistic regression models of associations between dog ownership and cardiometabolic disease were adjusted for age, sex, trauma load, mood disorder, substance abuse, nicotine abuse, and exercise. After adjustment, dog ownership was still associated with lower odds of hypertension and high cholesterol. Dog ownership also interacted with exercise to lower odds of heart disease and attenuated the effect of trauma load on hypertension. Conversely, age interacted with dog ownership such that odds of diabetes and stroke were higher in older Veterans who owned dogs.

Heart rate during sleep in PTSD patients: Moderation by contact with a service dog.

There is growing interest in the potential health benefits of dog ownership in both the lay and scientific communities. Large reductions in risk for cardiovascular disease and all-cause mortality in dog owners relative to non-owners have been observed in epidemiological samples. Persons diagnosed with posttraumatic stress disorder exhibit elevated risk for cardiovascular disease. The current study tested a sample of 45 U.S. military veterans with deployment-related posttraumatic stress disorder employing an intensive, longitudinal, within-subjects design contrasting sleep heart rate on nights with and without a service dog. As participants were engaged in residential psychiatric treatment, sleep opportunities, waking activities, meals, and medications, were consistently scheduled. The primary recording methodology, mattress actigraphy, enabled passive quantification of heart rate over a total sample of 1097 nights. Service dog contact was associated with reduced sleep heart rate especially in participants with more severe PTSD. Longer-term longitudinal studies will be needed to assess the durability and asymptotic magnitude of this effect. An unexpected effect of nights in study was associated with increased heart rate consistent with hospitalization-associated deconditioning.

Longitudinal profiles of sleep during residential PTSD treatment.

We investigated longitudinal profiles of objectively measured sleep periods (SP) over the course of residential treatment for posttraumatic stress disorder (PTSD) in a cohort of U.S. male veterans. Participants (N = 190) slept on mattress-actigraphy systems in a Veterans Affairs (VA) residential PTSD program. The final sample included 4078 sleep periods. Latent class mixed model analyses were used to identify between-subject profiles in sleep period durations, controlling for daily medication intake, over the first fifty days of residency. Logistic regression was used to determine the association of pre-treatment characteristics with identified profiles. Three longitudinal profiles of sleep period characterized most of the sample: 'stable' (56%), 'decreasing' (35%), and 'increasing' (8%). Less severe pre-treatment PTSD avoidance symptoms predicted membership in the 'decreasing' class and increased depression symptoms were predictive of membership in the 'increasing' class. Nearly half of the sample reported a summary change of 1 h or more over the course of the initial 50-nights in the program. Future work is needed to identify how these profiles might drive inpatient treatment decisions regarding the provision of adjunctive sleep-focused treatment such as cognitive-behavioral treatment for insomnia or hypnotic medications.

Sleep Spindles Favor Emotion Regulation Over Memory Consolidation of Stressors in Posttraumatic Stress Disorder.

BACKGROUND: Posttraumatic stress disorder (PTSD) is a trauma-induced condition, characterized by intrusive memories and trauma-associated anxiety. Non-rapid eye movement (NREM) sleep spindles might play a crucial role in learning and consolidating declarative stressor information. However, sleep and possibly sleep spindles are also known to regulate anxiety, suggestive of a dual role for sleep spindles in the processing of stressors. Specifically, in individuals with high PTSD symptom burden, spindles might fail to regulate anxiety levels after exposure and instead might maladaptively consolidate stressor information. METHODS: To disentangle the role of spindles in declarative memory versus anxiety regulation after stressor exposure and to examine the role of PTSD in these processes, we measured nap sleep after a cohort of 45 trauma-exposed participants were exposed to laboratory stress. Participants (high vs. low PTSD symptoms) completed 2 visits: a stress visit involving exposure to negatively valent images before nap and a control visit. In both visits, sleep was monitored via electroencephalography. A stressor recall session occurred after the nap in the stress visit. RESULTS: Stage 2 NREM (NREM2) spindle rates were higher in stress versus control sleep, indicative of stress-induced changes in spindles. In participants with high PTSD symptoms, NREM2 spindle rates in stress sleep predicted poorer recall accuracy of stressor images relative to participants with low PTSD symptoms, while correlating with greater reduction in stressor-induced anxiety levels after sleep. CONCLUSIONS: Contrary to our expectations, although spindles are known to play a role in declarative memory processes, our findings highlight an important role for spindles in sleep-dependent anxiety regulation in PTSD.

The sleep physiology of nightmares in veterans with psychological trauma: Evaluation of a dominant model using participant-applied electroencephalography in the home environment.

Nightmares are a core feature of posttraumatic stress disorder, are poorly understood, and are associated with serious negative outcomes. Their biology has been difficult to study, and the feasibility of capturing them in the naturalistic home environment has been poor. This said, the published research and dominant scientific model has focused on nightmares as a manifestation of noradrenergic hyperarousal during rapid eye movement sleep. The current study used at-home, participant-applied devices to measure nightmare physiology in posttraumatic stress disorder treatment-seeking veterans, by examining heartrate measures as indicators of noradrenergic tone, and sleep-stage characteristics and stability in the sleep preceding time-stamped nightmare awakenings. Our data indicate the high feasibility of participant-administered, at-home measurement, and showed an unexpected stability of -rapid eye movement sleep along with no evidence of heartrate elevations in sleep preceding nightmare awakenings. Altogether, these data highlight new opportunities for the study of nightmares while questioning the sufficiency of dominant models, which to date are largely theoretically based.

Autonomic regulation during sleep in PTSD.

The following article reviews the existing data on autonomic nervous system status in posttraumatic stress disorder. This review is embedded in a framework that considers the comparative ethology of sleep under threat. In sum, the current literature, though still quite limited, supports a role for impaired parasympathetic drive but not for increased sympathetic drive in the periphery during sleep in PTSD. Understanding this domain better can be expected to provide insights into the elevated prevalence of cardiovascular disease in posttraumatic stress disorder (PTSD) and may help to identify as-yet unrecognized medical comorbidities. Measurement issues and future opportunities are considered.

Reading the mind in the eyes in PTSD: Limited Moderation by the presence of a service dog.

Persons with posttraumatic stress disorder (PTSD) frequently experience relationship failures in family and occupational domains resulting in loss of social supports. Prior research has implicated impairments in social cognition. The Reading the Mind in the Eyes Test (RMET) measures a key component of social cognition, the ability to infer the internal states of other persons based on features of the eyes region of the face; however, studies administering this popular test to persons with PTSD have yielded mixed results. This study assessed RMET performance in 47 male U.S. military Veterans with chronic, severe PTSD. Employing a within-subjects design that avoided selection biases, it aimed specifically to determine whether components of RMET performance, including accuracy, response latency, and stimulus dwell time, were improved by the company of a service dog, an intervention that has improved social function in other populations. RMET accuracies and response latencies in this PTSD sample were in the normal range. The presence of a familiar service dog did not improve RMET accuracy, reduce response latencies, or increase dwell times. Dog presence increased the speed of visual scanning perhaps consistent with reduced social fear.

The relationship of fear-potentiated startle and polysomnography-measured sleep in trauma-exposed men and women with and without PTSD: testing REM sleep effects and exploring the roles of an integrative measure of sleep, PTSD symptoms, and biological sex.

STUDY OBJECTIVES: Published research indicates that sleep is involved in emotional information processing. Using a fear-potentiated startle (FPS) and nap sleep protocol, we examined the relationship of emotional learning with REM sleep (REMS) in trauma-exposed participants. We also explored the roles of posttraumatic stress disorder (PTSD) symptoms, biological sex, and an integrative measure of polysomnography-measured (PSG) sleep in the learning-sleep relationship. METHODS: After an adaptation nap, participants (N = 46) completed two more visits (counterbalanced): a stress-condition visit, which included FPS conditioning procedures prior to a nap and assessment of learning retention and fear extinction training after the nap, and a control visit, which included a nap opportunity without stressful procedures. FPS conditioning included a "fear" visual stimulus paired with an air blast to the neck and a "safety" visual stimulus never paired with an air blast. Retention and extinction involved presentation of the visual stimuli without the air blast. Primary analyses examined the relationship between FPS responses pre- and post-sleep with stress-condition REMS duration, controlling for control-nap REMS duration. RESULTS: Higher safety learning predicted increased REMS and increased REMS predicted more rapid extinction learning. Similar relationships were observed with an integrative PSG sleep measure. They also showed unexpected effects of PTSD symptoms on learning and showed biological sex effects on learning-sleep relationships. CONCLUSIONS: Findings support evidence of a relationship between adaptive emotional learning and REMS. They underscore the importance of examining sex effects in sleep-learning relationships. They introduce an integrative PSG sleep measure with potential relevance to studies of sleep and subjective and biological outcomes.

Regional gray matter oligodendrocyte- and myelin-related measures are associated with differential susceptibility to stress-induced behavior in rats and humans.

Individual reactions to traumatic stress vary dramatically, yet the biological basis of this variation remains poorly understood. Recent studies demonstrate the surprising plasticity of oligodendrocytes and myelin with stress and experience, providing a potential mechanism by which trauma induces aberrant structural and functional changes in the adult brain. In this study, we utilized a translational approach to test the hypothesis that gray matter oligodendrocytes contribute to traumatic-stress-induced behavioral variation in both rats and humans. We exposed adult, male rats to a single, severe stressor and used a multimodal approach to characterize avoidance, startle, and fear-learning behavior, as well as oligodendrocyte and myelin basic protein (MBP) content in multiple brain areas. We found that oligodendrocyte cell density and MBP were correlated with behavioral outcomes in a region-specific manner. Specifically, stress-induced avoidance positively correlated with hippocampal dentate gyrus oligodendrocytes and MBP. Viral overexpression of the oligodendrogenic factor Olig1 in the dentate gyrus was sufficient to induce an anxiety-like behavioral phenotype. In contrast, contextual fear learning positively correlated with MBP in the amygdala and spatial-processing regions of the hippocampus. In a group of trauma-exposed US veterans, T1-/T2-weighted magnetic resonance imaging estimates of hippocampal and amygdala myelin associated with symptom profiles in a region-specific manner that mirrored the findings in rats. These results demonstrate a species-independent relationship between region-specific, gray matter oligodendrocytes and differential behavioral phenotypes following traumatic stress exposure. This study suggests a novel mechanism for brain plasticity that underlies individual variance in sensitivity to traumatic stress.

Tracking positive and negative affect in PTSD inpatients during a service dog intervention.

Though popular across many audiences, engagement with a service dog has undergone limited empirical evaluation as a complementary or alternative treatment for posttraumatic stress disorder (PTSD). The present study took advantage of a service dog training intervention underway in a Department of Veterans Affairs residential PTSD treatment program to perform a within-subjects comparison of a range of phenotypic markers. The present report considers negative and positive affect, assessed throughout the day, contrasting weeks when participants were or were not accompanied by their service dog. Fifty-four veterans were studied for 2-6 weeks. Negative and positive affect were sampled five times per day using items from the Positive and Negative Affect Schedule. Participants also wore a single-patch ECG/activity recorder and slept on beds recording sleep actigraphically. Linear mixed effects regression was employed to estimate the effect of the presence of service dog on momentary affect in the context of other presumable influences. Missing data were managed using methods applicable to random and nonrandom missingness. In this sample, the presence of a service dog was associated with reduced negative and increased positive affect, with both effects diminishing over time. Only negative affect was associated with time in residential treatment, and only positive affect was associated with concurrent heart rate, activity, and the interaction of activity and prior-night actigraphic sleep efficiency. These results concur with prior reports of reduced PTSD symptomology in association with the presence of a service dog, and with the distinct neurocircuitries underlying defensive and appetitive emotion and motivation. Limitations derive from the artificial environment and brief duration of study. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Sleep/Wake Detection by Behavioral Response to Haptic Stimuli.

STUDY OBJECTIVES: Actigraphy, the tool of choice for assessment of sleep phase disorders, is insensitive to movement-free waking. This study aimed to determine whether the detection of waking could be performed by recording instrumental responses to haptic stimuli delivered by a low-cost device. METHODS: Twenty adults underwent 2 nights of laboratory polysomnography (PSG) while wearing a fingerless glove under which a stimulating actigraph ("Wakemeter") was apposed to the palm. The Wakemeter, controlled by a tablet computer, delivered gentle, haptic stimuli every 10 minutes during the sleep period. If a stimulus was detected, the participant squeezed the Wakemeter. Stimulus times, response times and movements were streamed to the tablet. Concurrent PSG data were scored blind to stimuli and responses. Self-reported sleep quality ratings were collected each morning. RESULTS: The Wakemeter was acceptable to 19 of 20 participants, and effects on self-reported and objective sleep were small. The probability of a response to the stimulus during a wake epoch was high regardless of movement. In contrast, actigraphy magnitude distributions were indistinguishable across epochs scored wake without movement versus sleep, confirming a known limitation of actigraphy. A simple method for calculating sleep efficiency from responses to the stimuli yielded estimates that were highly correlated with PSG-derived estimates (rho = .69, P < .001). CONCLUSIONS: Behavioral responses to haptic stimuli detected epochs of movement-free wake during the sleep period and may augment actigraphy in the low-burden estimation of sleep efficiency. Acceptability of the method over longer recording periods remains to be established.

Increased epoch-to-epoch parasympathetic cardiac regulation in participants with posttraumatic stress disorder compared to those with panic disorder and control participants.

BACKGROUND: Research on the link between respiratory sinus arrhythmia (RSA) and posttraumatic stress disorder (PTSD) has largely focused on average levels of RSA. However, given that rapid shifts in parasympathetic tone are necessary to maintain adaptive cardiac variability, the exclusive focus on these tonic estimates provides an incomplete quantification of parasympathetic cardiac regulation. METHOD: The present study is a secondary analysis of previously published data. This analysis aimed to address this limitation by examining the dynamic regulatory effect of the parasympathetic nervous system on heart rate. As such, we examined epoch-to-epoch parasympathetic cardiac regulation - operationalized as the lagged relationship between RSA and heart rate (HR) across consecutive 30-s epochs - across a single night in participants with PTSD, panic disorder (PD), comorbid PTSD and PD (PTSD + PD), and healthy controls. Electrocardiogram and respiratory signals were continuously recorded from 23 participants with PTSD, 14 with PD, 16 with PTSD + PD, and 16 control participants over a single night of sleep in a laboratory setting. RESULTS: No group differences in tonic RSA were observed; however, participants with PTSD only and PTSD + PD exhibited significantly greater epoch-to-epoch parasympathetic cardiac regulation over the night than those with PD only and control participants. Moreover, greater severity of hyperarousal symptoms was significantly associated with increased epoch-to-epoch parasympathetic cardiac regulation among participants with PTSD only and PTSD + PD. DISCUSSION: These data provide preliminary evidence for an upregulatory parasympathetic response to self-reported hyperarousal in participants with PTSD only and PTSD + PD reflected by increased epoch-to-epoch parasympathetic cardiac regulation.

Two Independent Predictors of Nightmares in Posttraumatic Stress Disorder.

STUDY OBJECTIVES: Understanding nightmares (NM) and disturbing dreams (DD) in posttraumatic stress disorder (PTSD) has been limited by the unpredictability of these events and their nonappearance in the sleep laboratory. This study used intensive, longitudinal, ambulatory methods to predict morning reports of NM/DD in veterans in whom chronic, severe PTSD was diagnosed. METHODS: Participants were 31 male United States military veterans engaged in residential treatment for PTSD and participating in a service animal training intervention. Participants slept on mattress actigraphs and provided reports of momentary mood, as well as morning NM/DD reports, for up to 6 weeks. Mattress actigraphy provided sleep-period heart rate and respiratory sinus arrhythmia (RSA), and an actigraphic estimate of sleep efficiency. On one night, a respiratory event index (REI) was obtained using an ambulatory system. RESULTS: A total of 468 morning reports were obtained, of which 282 endorsed NM/DD during the prior night, and 186 did not. After accounting for multiple predictors, only elevated REI and lower prior-night sleep RSA predicted morning endorsement of NM/DD. These two predictors did not interact. CONCLUSIONS: Elevated REI and lower sleep period RSA were independently predictive of NM/DD. The former result is consistent with studies showing that sleep-disordered breathing (SDB) is a factor in NM/DD, and that continuous positive airway pressure (CPAP) can reduce these symptoms in patients with comorbid PTSD and SDB. The latter result implicates dysregulated arousal modulation during sleep in trauma-related NM/DD. It is consistent with findings that NM/DD are reported in patients without SDB and can persist in patients with comorbid PTSD and SDB even when CPAP successfully remediates SDB.

Calibrating actigraphy to improve sleep efficiency estimates.

Actigraphy (ACT) can enhance treatment for insomnia by providing objective estimates of sleep efficiency; however, only two studies have assessed the accuracy of actigraphy-based estimates of sleep efficiency (ACT-SE) in sleep-disordered samples studied at home. Both found poor correspondence with polysomnography-based estimates (PSG-SE). The current study tested that concordance in a third sample and piloted a method for improving ACT-SE. Participants in one of four diagnostic categories (panic disorder, post-traumatic stress disorder, comorbid post-traumatic stress and panic disorder and controls without sleep complaints) underwent in-home recording of sleep using concurrent ambulatory PSG and actigraphy. Precisely synchronized PSG and ACT recordings were obtained from 41 participants. Sleep efficiency was scored independently using conventional methods, and ACT-SE/PSG-SE concordance examined. Next, ACT data recorded initially at 0.5 Hz were resampled to 30-s epochs and rescaled on a per-participant basis to yield optimized concordance between PSG- and ACT-based sleep efficiency estimates. Using standard scoring of ACT, the correlation between ACT-SE and PSG-SE across participants was statistically significant (r = 0.35, P < 0.025), although ACT-SE failed to replicate a main effect of diagnosis. Individualized calibration of ACT against a night of PSG yielded a significantly higher correlation between ACT-SE and PSG-SE (r = 0.65, P < 0.001; z = 1.692, P = 0.0452, one-tailed) and a significant main effect of diagnosis that was highly correspondent with the effect on PSG-SE. ACT-based estimates of sleep efficiency in sleep-disordered patients tested at home can be improved significantly by calibration against a single night of concurrent PSG.

Canine companionship is associated with modification of attentional bias in posttraumatic stress disorder.

Attentional bias towards aversive stimuli has been demonstrated in the anxiety disorders and in posttraumatic stress disorder, and attentional bias modification has been proposed as a candidate treatment. This study rigorously assessed attentional bias towards aversive and pleasant visual imagery associated with the presence or absence of a familiar service canine in 23 veterans with chronic military-related posttraumatic stress disorder. Participants were repeatedly tested with and without their service canines present on two tasks designed to elicit spontaneous visual attention to facial and scenic image pairs, respectively. Each stimulus contrasted an emotive image with a neutral image. Via eye-tracking, the difference in visual attention directed to each image was analyzed as a function of the valence contrast and presence/absence of the canine. Across both tasks, the presence of a familiar service canine attenuated the normative attentional bias towards aversive image content. In the facial task, presence of the service canine specifically reduced attention toward angry faces. In that task, as well, accumulated days with the service canine similarly modulated attention toward facial emotion. The results suggest that the presence of a familiar service canine is associated with attenuation of attentional bias to aversive stimuli in chronic military-service-related posttraumatic stress disorder. Questions remain regarding the generalization of such effects to other populations, their dependence on the familiarity, breed, and training of the canine, and on social context.

Salivary Cortisol and Regional Brain Volumes Among Veterans With and Without Posttraumatic Stress Disorder.

BACKGROUND: Human studies have often found that brain regions rich in glucocorticoid receptors exhibit smaller volume in samples with past trauma and ongoing stress; however, relatively little research has addressed the hypothesis that such smaller volumes can be traced to elevated circulating glucocorticoid hormones (GCs). This issue takes on renewed interest in light of recent proposals to treat symptoms of stress disorders such as posttraumatic stress disorder (PTSD) with exogenous synthetic GCs. We sought to examine the relation of circulating GCs to brain macrostructure among veterans with and without PTSD. METHODS: Participants (n = 90) included combat veterans with and without PTSD. Veterans completed self-report surveys, home-based cortisol samples, reactive cortisol samples over the course of two serial Trier Social Stress Tests, a low-dose dexamethasone suppression test, and structural magnetic resonance brain imaging over the course of 3 to 5 days. RESULTS: No associations were observed between any salivary cortisol index and the volumes of the hippocampus or amygdala. A negative association was observed between evening basal cortisol and both FreeSurfer global volume and BrainImage supratentorial tissue volume. This effect was moderated by PTSD. Also observed was a positive association between reactive cortisol and these same brain volumes. CONCLUSIONS: Estimates of cortical but not hippocampal or amygdala volume were moderately associated with evening basal salivary cortisol and cortisol reactivity to a social stressor. Existing models relating GC receptor density, circulating cortisol levels, and regional brain volumes received little support.

Preliminary Evidence of Increased Hippocampal Myelin Content in Veterans with Posttraumatic Stress Disorder.

Recent findings suggest the formation of myelin in the central nervous system by oligodendrocytes is a continuous process that can be modified with experience. For example, a recent study showed that immobilization stress increased oligodendrogensis in the dentate gyrus of adult rat hippocampus. Because changes in myelination represents an adaptive form of brain plasticity that has a greater reach in the adult brain than other forms of plasticity (e.g., neurogenesis), the objective of this "proof of concept" study was to examine whether there are differences in myelination in the hippocampi of humans with and without post-traumatic stress disorder (PTSD). We used the ratio of T1-weighted/T2-weighted magnetic resonance image (MRI) intensity to estimate the degree of hippocampal myelination in 19 male veterans with PTSD and 19 matched trauma-exposed male veterans without PTSD (mean age: 43 ± 12 years). We found that veterans with PTSD had significantly more hippocampal myelin than trauma-exposed controls. There was also found a positive correlation between estimates of hippocampal myelination and PTSD and depressive symptom severity. To our knowledge, this is the first study to examine hippocampal myelination in humans with PTSD. These results provide preliminary evidence for stress-induced hippocampal myelin formation as a potential mechanism underlying the brain abnormalities associated with vulnerability to stress.