Structural Neuroimaging of Hippocampus and Amygdala Subregions in Posttraumatic Stress Disorder: A Scoping Review

Numerous studies have explored the relationship between posttraumatic stress disorder (PTSD) and the hippocampus and the amygdala because both regions are implicated in the disorder's pathogenesis and pathophysiology. Nevertheless, those key limbic regions consist of functionally and cytoarchitecturally distinct substructures that may play different roles in the etiology of PTSD. Spurred by the availability of automatic segmentation software, structural neuroimaging studies of human hippocampal and amygdala subregions have proliferated in recent years. Here, we present a preregistered scoping review of the existing structural neuroimaging studies of the hippocampus and amygdala subregions in adults diagnosed with PTSD. A total of 3513 studies assessing subregion volumes were identified, 1689 of which were screened, and 21 studies were eligible for this review (total N = 2876 individuals). Most studies examined hippocampal subregions and reported decreased CA1, CA3, dentate gyrus, and subiculum volumes in PTSD. Fewer studies investigated amygdala subregions and reported altered lateral, basal, and central nuclei volumes in PTSD. This review further highlights the conceptual and methodological limitations of the current literature and identifies future directions to increase understanding of the distinct roles of hippocampal and amygdalar subregions in posttraumatic psychopathology.

Attention, attention! Posttraumatic stress disorder is associated with altered attention-related brain function

Posttraumatic stress disorder (PTSD) is a debilitating condition characterized by altered arousal, mood, and cognition. Studies report attentional alterations such as threat bias in individuals with PTSD, though this work has largely been conducted within emotionally-charged contexts (e.g., threatening stimuli). Emerging behavioral evidence suggests that PTSD-related attention deficits exist even in the absence of threatening cues or anxiety triggers. However, the role and functioning of attention brain circuits as they relate to PTSD remains underexplored. In this mini review, we highlight recent work using non-emotional stimuli to investigate the neurobiology of attention and disruptions to attention-related brain function among individuals with PTSD. We then discuss gaps in the current literature, including questions pertaining to the neural circuitry of attentional alterations in PTSD, as well as the contributions that trauma exposure, PTSD symptoms, comorbidities, and pre-existing vulnerabilities may have in this relationship. Finally, we suggest future directions for this emerging area of research, which may further inform knowledge surrounding the neurobiological underpinnings of PTSD and potential treatments.

Attention deficits as a key player in the symptomatology of posttraumatic stress disorder: A review

Posttraumatic stress disorder (PTSD) is a debilitating psychiatric disorder characterized by symptoms such as re-experiencing of the psychotrauma and hyperarousal. Although current literature mainly discusses the emotionally related aspects of these symptoms, studies also highlight the relation between re-experiencing, hyperarousability, and attention deficits, which are associated with poorer daily function and reduced quality of life. This review provides a comprehensive analysis of the existing research on attention deficits among adults with PTSD. A systematic search through five databases resulted in the inclusion of 48 peer-reviewed, English-language articles, describing 49 distinct studies. Using a total of 47 different attentional assessment tools, the majority of studies investigated sustained (n = 40), divided (n = 16), or selective (n = 14) attention. A total of 30 studies (61.2%) found significant correlations between PTSD symptoms and attention deficits, and 10 studies (20.4%) found that higher levels of attention deficits were predictive of worse PTSD symptoms. Moreover, neuroimaging results of six (f)MRI and three EEG studies identified various potential neurobiological pathways involved, including (pre)frontal attention networks. Together, the body of research shows that attention deficits in individuals with PTSD are common and occur in surroundings with emotionally neutral stimuli. Nonetheless, current treatment strategies do not target these attentional difficulties. We propose a novel perspective to PTSD diagnosis and treatment strategies based on attention deficits and their relation with top-down regulation of re-experiencing and subsequent other PTSD symptoms.

Evaluating the Evidence for Brain-Based Biotypes of Psychiatric Vulnerability in the Acute Aftermath of Trauma

OBJECTIVE

The weak link between subjective symptom-based diagnostic methods for posttraumatic psychopathology and objectively measured neurobiological indices forms a barrier to the development of effective personalized treatments. To overcome this problem, recent studies have aimed to stratify psychiatric disorders by identifying consistent subgroups based on objective neural markers. Along these lines, a promising 2021 study by Stevens et al. identified distinct brain-based biotypes associated with different longitudinal patterns of posttraumatic symptoms. Here, the authors conducted a conceptual nonexact replication of that study using a comparable data set from a multimodal longitudinal study of recent trauma survivors.

METHODS

A total of 130 participants (mean age, 33.61 years, SD=11.21; 48% women) admitted to a general hospital emergency department following trauma exposure underwent demographic, clinical, and neuroimaging assessments 1, 6, and 14 months after trauma. All analyses followed the pipeline outlined in the original study and were conducted in collaboration with its authors.

RESULTS

Task-based functional MRI conducted 1 month posttrauma was used to identify four clusters of individuals based on profiles of neural activity reflecting threat and reward reactivity. These clusters were not identical to the previously identified brain-based biotypes and were not associated with prospective symptoms of posttraumatic psychopathology.

CONCLUSIONS

Overall, these findings suggest that the original brain-based biotypes of trauma resilience and psychopathology may not generalize to other populations. Thus, caution is warranted when attempting to define subtypes of psychiatric vulnerability using neural indices before treatment implications can be fully realized. Additional replication studies are needed to identify more stable and generalizable neuroimaging-based biotypes of posttraumatic psychopathology.

Functional Connectome-Based Predictive Modeling in Autism

Autism is a heterogeneous neurodevelopmental condition, and functional magnetic resonance imaging-based studies have helped advance our understanding of its effects on brain network activity. We review how predictive modeling, using measures of functional connectivity and symptoms, has helped reveal key insights into this condition. We discuss how different prediction frameworks can further our understanding of the brain-based features that underlie complex autism symptomatology and consider how predictive models may be used in clinical settings. Throughout, we highlight aspects of study interpretation, such as data decay and sampling biases, that require consideration within the context of this condition. We close by suggesting exciting future directions for predictive modeling in autism.

PTSD symptomatology is selectively associated with impaired sustained attention ability and dorsal attention network synchronization

Posttraumatic Stress Disorder (PTSD) symptomatology is associated with dysregulated sustained attention, which produces functional impairments. Performance on sustained attention paradigms such as continuous performance tasks are influenced by both the ability to sustain attention and response strategy. However, previous studies have not dissociated PTSD-related associations with sustained attention ability and strategy, which limits characterization of neural circuitry underlying PTSD-related attentional impairments. Therefore, we characterized and replicated PTSD-related associations with sustained attention ability and response strategy in trauma-exposed Veterans, which guided characterization of PTSD-related differences in neural circuit function. In Study 1, PTSD symptoms were selectively associated with reduced sustained attention ability, but not more impulsive response strategies. In Study 2, we utilized task and resting-state fMRI to characterize neural circuitry underlying PTSD-related differences in sustained attention ability. Both PTSD symptomatology and sustained attention ability exhibited converging associations with reduced dorsal attention network (DAN) synchronization to endogeneous attentional fluctuations. Post-hoc time course analyses demonstrated that PTSD symptoms were most accurately characterized by delayed, rather than globally reduced, DAN synchronization to endogenous attentional fluctuations. Together, these findings suggest that PTSD symptomatology may selectively impair sustained attention ability by disrupting proactive engagement of attentional control circuitry.

Dividing attention during the Timed Up and Go enhances associations of several subtask performances with MCI and cognition

We tested the hypothesis that dividing attention would strengthen the ability to detect mild cognitive impairment (MCI) and specific cognitive abilities from Timed Up and Go (TUG) performance in the community setting. While wearing a belt-worn sensor, 757 dementia-free older adults completed TUG during two conditions, with and without a concurrent verbal serial subtraction task. We segmented TUG into its four subtasks (i.e., walking, turning, and two postural transitions), and extracted 18 measures that were summarized into nine validated sensor metrics. Participants also underwent a detailed cognitive assessment during the same visit. We then employed a series of regression models to determine the combinations of subtask sensor metrics most strongly associated with MCI and specific cognitive abilities for each condition. We also compared subtask performances with and without dividing attention to determine whether the costs of divided attention were associated with cognition. While slower TUG walking and turning were associated with higher odds of MCI under normal conditions, these and other subtask associations became more strongly linked to MCI when TUG was performed under divided attention. Walking and turns were also most strongly associated with executive function and attention, particularly under divided attention. These differential associations with cognition were mirrored by performance costs. However, since several TUG subtasks were more strongly associated with MCI and cognitive abilities when performed under divided attention, future work is needed to determine how instrumented dual-task TUG testing can more accurately estimate risk for late-life cognitive impairment in older adults.

An executive function subtype of PTSD with unique neural markers and clinical trajectories

Previous work identified a cognitive subtype of PTSD with impaired executive function (i.e., impaired EF-PTSD subtype) and aberrant resting-state functional connectivity between frontal parietal control (FPCN) and limbic (LN) networks. To better characterize this cognitive subtype of PTSD, this study investigated (1) alterations in specific FPCN and LN subnetworks and (2) chronicity of PTSD symptoms. In a post-9/11 veteran sample (N = 368, 89% male), we identified EF subgroups using a standardized neuropsychological battery and a priori cutoffs for impaired, average, and above-average EF performance. Functional connectivity between two subnetworks of the FPCN and three subnetworks of the LN was assessed using resting-state fMRI (n = 314). PTSD chronicity over a 1-2-year period was assessed using a reliable change index (n = 175). The impaired EF-PTSD subtype had significantly reduced negative functional connectivity between the FPCN subnetwork involved in top-down control of emotion and two LN subnetworks involved in learning/memory and social/emotional processing. This impaired EF-PTSD subtype had relatively chronic PTSD, while those with above-average EF and PTSD displayed greater symptom reduction. Lastly, FPCN-LN subnetworks partially mediated the relationship between EF and PTSD chronicity (n = 121). This study reveals (1) that an impaired EF-PTSD subtype has a specific pattern of FPCN-LN subnetwork connectivity, (2) a novel above-average EF-PTSD subtype displays reduced PTSD chronicity, and (3) both cognitive and neural functioning predict PTSD chronicity. The results indicate a need to investigate how individuals with this impaired EF-PTSD subtype respond to treatment, and how they might benefit from personalized and novel approaches that target these neurocognitive systems.

What have we really learned from functional connectivity in clinical populations?

Functional connectivity (FC), or the statistical interdependence of blood-oxygen dependent level (BOLD) signals between brain regions using fMRI, has emerged as a widely used tool for probing functional abnormalities in clinical populations due to the promise of the approach across conceptual, technical, and practical levels. With an already vast and steadily accumulating neuroimaging literature on neurodevelopmental, psychiatric, and neurological diseases and disorders in which FC is a primary measure, we aim here to provide a high-level synthesis of major concepts that have arisen from FC findings in a manner that cuts across different clinical conditions and sheds light on overarching principles. We highlight that FC has allowed us to discover the ubiquity of intrinsic functional networks across virtually all brains and clarify typical patterns of neurodevelopment over the lifespan. This understanding of typical FC maturation with age has provided important benchmarks against which to evaluate divergent maturation in early life and degeneration in late life. This in turn has led to the important insight that many clinical conditions are associated with complex, distributed, network-level changes in the brain, as opposed to solely focal abnormalities. We further emphasize the important role that FC studies have played in supporting a dimensional approach to studying transdiagnostic clinical symptoms and in enhancing the multimodal characterization and prediction of the trajectory of symptom progression across conditions. We highlight the unprecedented opportunity offered by FC to probe functional abnormalities in clinical conditions where brain function could not be easily studied otherwise, such as in disorders of consciousness. Lastly, we suggest high priority areas for future research and acknowledge critical barriers associated with the use of FC methods, particularly those related to artifact removal, data denoising and feasibility in clinical contexts.

Apolipoprotein E (APOE) ε4 moderates the relationship between c-reactive protein, cognitive functioning, and white matter integrity

Elevated serum C-reactive protein (CRP) and possessing an APOE ε4 allele are two of the most prominent risk factors for cognitive and neurological dysfunction in older adults, but little is known about the unique or cumulative effects of these risk factors in young-to-middle-aged adults. To further characterize these potential relationships, measures of cognition and microstructural white matter integrity were examined using data from a sample of 329 post-9/11 war veterans that was collected as part of a comprehensive evaluation that included assessment of neuropsychological functioning, MRI scanning, psychiatric diagnoses, health screening, markers of inflammation, and APOE genotypes. Hierarchical linear regression analyses revealed the CRP and APOE ε4 interaction was associated with global cognition (β = -0.633), executive functioning (β = -0.566), and global fractional anisotropy (β = -0.470), such that elevated CRP was associated with worse cognition and white matter integrity in APOE ε4 carriers. Diffusion tensor imaging (DTI) was used to determine if CRP × APOE ε4 presence was associated with regionally specific fractional anisotropy in white matter tracts. Tract-based spatial statistics revealed CRP × APOE ε4 presence was associated with fractional anisotropy in the corpus callosum, right superior longitudinal fasciculus, right posterior corona radiata, as well as the bilateral anterior and superior corona radiatas. This suggests that APOE ε4 carriers may be uniquely vulnerable to the potentially negative impact of elevated systematic inflammation to cognition and microstructural white matter integrity.

Teasing apart trauma: neural oscillations differentiate individual cases of mild traumatic brain injury from post-traumatic stress disorder even when symptoms overlap

Post-traumatic stress disorder (PTSD) and mild traumatic brain injury (mTBI) are highly prevalent and closely related disorders. Affected individuals often exhibit substantially overlapping symptomatology - a major challenge for differential diagnosis in both military and civilian contexts. According to our symptom assessment, the PTSD group exhibited comparable levels of concussion symptoms and severity to the mTBI group. An objective and reliable system to uncover the key neural signatures differentiating these disorders would be an important step towards translational and applied clinical use. Here we explore use of MEG (magnetoencephalography)-multivariate statistical learning analysis in identifying the neural features for differential PTSD/mTBI characterisation. Resting state MEG-derived regional neural activity and coherence (or functional connectivity) across seven canonical neural oscillation frequencies (delta to high gamma) were used. The selected features were consistent and largely confirmatory with previously established neurophysiological markers for the two disorders. For regional power from theta, alpha and high gamma bands, the amygdala, hippocampus and temporal areas were identified. In line with regional activity, additional connections within the occipital, parietal and temporal regions were selected across a number of frequency bands. This study is the first to employ MEG-derived neural features to reliably and differentially stratify the two disorders in a multi-group context. The features from alpha and beta bands exhibited the best classification performance, even in cases where distinction by concussion symptom profiles alone were extremely difficult. We demonstrate the potential of using 'invisible' neural indices of brain functioning to understand and differentiate these debilitating conditions.

Impaired executive function exacerbates neural markers of posttraumatic stress disorder

BACKGROUND

A major obstacle in understanding and treating posttraumatic stress disorder (PTSD) is its clinical and neurobiological heterogeneity. To address this barrier, the field has become increasingly interested in identifying subtypes of PTSD based on dysfunction in neural networks alongside cognitive impairments that may underlie the development and maintenance of symptoms. The current study aimed to determine if subtypes of PTSD, based on normative-based cognitive dysfunction across multiple domains, have unique neural network signatures.

METHODS

In a sample of 271 veterans (90% male) that completed both neuropsychological testing and resting-state fMRI, two complementary, whole-brain functional connectivity analyses explored the link between brain functioning, PTSD symptoms, and cognition.

RESULTS

At the network level, PTSD symptom severity was associated with reduced negative coupling between the limbic network (LN) and frontal-parietal control network (FPCN), driven specifically by the dorsolateral prefrontal cortex and amygdala Hubs of Dysfunction. Further, this relationship was uniquely moderated by executive function (EF). Specifically, those with PTSD and impaired EF had the strongest marker of LN-FPCN dysregulation, while those with above-average EF did not exhibit PTSD-related dysregulation of these networks.

CONCLUSION

These results suggest that poor executive functioning, alongside LN-FPCN dysregulation, may represent a neurocognitive subtype of PTSD.

Defining focal brain stimulation targets for PTSD using neuroimaging

INTRODUCTION

Focal brain stimulation has potential as a treatment for posttraumatic stress disorder (PTSD). In this review, we aim to inform selection of focal brain stimulation targets for treating PTSD by examining studies of the functional neuroanatomy of PTSD and treatment response. We first briefly review data on brain stimulation interventions for PTSD. Although published data suggest good efficacy overall, the neurobiological rationale for each stimulation target is not always clear.

METHODS

Therefore, we assess pre- and post-treatment (predominantly psychotherapy) functional neuroimaging studies in PTSD to determine which brain changes seem critical to treatment response. Results of these studies are presented within a previously proposed functional neural systems model of PTSD.

RESULTS

While not completely consistent, research suggests that downregulating the fear learning and threat and salience detection circuits (i.e., amygdala, dorsal anterior cingulate cortex and insula) and upregulating the emotion regulation and executive function and contextual processing circuits (i.e., prefrontal cortical regions and hippocampus) may mediate PTSD treatment response.

CONCLUSION

This literature review provides some justification for current focal brain stimulation targets. However, the examination of treatment effects on neural networks is limited, and studies that include the stimulation targets are lacking. Further, additional targets, such as the cingulate, medial prefrontal cortex, and inferior parietal lobe, may also be worth investigation, especially when considering how to achieve network level changes. Additional research combining PTSD treatment with functional neuroimaging will help move the field forward by identifying and validating novel targets, providing better rationale for specific treatment parameters and personalizing treatment for PTSD.

Connectome-based functional connectivity markers of suicide attempt

BACKGROUND

Functional brain markers of suicidality can help identify at-risk individuals and uncover underlying neurocognitive mechanism(s). Although some converging evidence has implicated dysfunction in several brain networks, suicide-related neuroimaging markers are inconsistent across studies, due to heterogeneity of neuroimaging approaches, clinical populations, and experimental methods.

METHODS

The current study aimed to address these limitations by examining resting-fMRI connectivity in a sample of post-9/11 veterans with a past suicide attempt (SA; n = 16) compared to a psychiatric control group (PC; n = 124) with no SA history but comparable past and present symptomatology, as well as a trauma control group (TC; n = 66) of trauma-exposed healthy controls. We used both a novel graph-analytic and seed-based approach to characterize SA-related connectivity differences across brain networks.

RESULTS

First, the graph-analytic approach identified the right amygdala and a region in the cognitive control network (right middle temporal gyrus; MTG) as regional SA-related hubs of dysfunction (HoD), or regions that exhibited a high number of SA-related connections. Aberrant SA-related connectivity between these hubs spanned multiple networks, including the cognitive control, default mode and visual networks. Second, the seed-based connectivity analysis that identifies SA-related differences in the strength of neural connections across the whole brain further implicated the right amygdala.

LIMITATIONS

Small sample size and potential underreporting of SA.

CONCLUSIONS

These two analytic approaches preliminarily suggest that the right amygdala and right MTG may be specific neural markers of SA that can be differentiated from neural markers of psychopathology more broadly.