Frontal Lobe Circuitry in Posttraumatic Stress Disorder

Associations Between Social Network Characteristics and Brain Structure Among Older Adults

INTRODUCTION

Social connectedness is associated with slower cognitive decline among older adults. Recent research suggests that distinct aspects of social networks may have differential effects on cognitive resilience, but few studies analyze brain structure.

METHODS

This study includes 117 cognitively impaired and 59 unimpaired older adults. The effects of social network characteristics (bridging/bonding) on brain regions of interests were analyzed using linear regressions and voxel-wise multiple linear regressions of gray matter density.

RESULTS

Increased social bridging was associated with greater bilateral amygdala volume and insular thickness, and left frontal lobe thickness, putamen, and thalamic volumes. Increased social bonding was associated with greater bilateral medial orbitofrontal and caudal anterior cingulate thickness, as well as right frontal lobe thickness, putamen, and amygdala volumes.

DISCUSSION

The associations between social connectedness and brain structure vary depending on the types of social enrichment accessible through social networks, suggesting that psychosocial interventions could mitigate neurodegeneration.

HIGHLIGHTS

Distinct forms of social capital are uniquely linked to gray matter density (GMD). Bridging is associated with preserved GMD in limbic system structures. Bonding is associated with preserved GMD in frontal lobe regions. Bridging is associated with increased brain reserve in sensory processing regions. Bonding is associated with increased brain reserve in regions of stress modulation.

Intrusive thinking: Circuit and synaptic mechanisms of a transdiagnostic psychiatric symptom

Spontaneous thought is an adaptive cognitive process that can produce novel and insightful thought sequences useful in guiding future behavior. In many psychiatric disorders, spontaneous thinking becomes intrusive and uncontrolled, and can trigger symptoms such as craving, repetitive negative thinking and trauma-related memories. We link studies using clinical imaging and rodent modeling towards understanding the neurocircuitry and neuroplasticity of intrusive thinking. We propose a framework in which drugs or stress change the homeostatic set point of brain reward circuitry, which then impacts subsequent plasticity induced by drug/stress conditioned cues (metaplastic allostasis). We further argue for the importance of examining not only the canonical pre- and postsynapse, but also the adjacent astroglial protrusions and extracellular matrix that together form the tetrapartite synapse and that plasticity throughout the tetrapartite synapse is necessary for cue-induced drug or stress behaviors. This analysis reveals that drug use or trauma cause long-lasting allostatic brain plasticity that sets the stage for subsequent drug/trauma-associated cues to induce transient plasticity that can lead to intrusive thinking.

Emotion dynamics as hierarchical Bayesian inference in time

What fundamental property of our environment would be most valuable and optimal in characterizing the emotional dynamics we experience in daily life? Empirical work has shown that an accurate estimation of uncertainty is necessary for our optimal perception, learning, and decision-making. However, the role of this uncertainty in governing our affective dynamics remains unexplored. Using Bayesian encoding, decoding and computational modeling, on a large-scale neuroimaging and behavioral data on a passive movie-watching task, we showed that emotions naturally arise due to ongoing uncertainty estimations about future outcomes in a hierarchical neural architecture. Several prefrontal subregions hierarchically encoded a lower-dimensional signal that highly correlated with the evolving uncertainty. Crucially, the lateral orbitofrontal cortex (lOFC) tracked the temporal fluctuations of this uncertainty and was predictive of the participants' predisposition to anxiety. Furthermore, we observed a distinct functional double-dissociation within OFC with increased connectivity between medial OFC and DMN, while with that of lOFC and FPN in response to the evolving affect. Finally, we uncovered a temporally predictive code updating an individual's beliefs spontaneously with fluctuating outcome uncertainty in the lOFC. A biologically relevant and computationally crucial parameter in the theories of brain function, we propose uncertainty to be central to the definition of complex emotions.

MEG neural signature of sexual trauma in women veterans with PTSD

Previous research has documented the utility of synchronous neural interactions (SNI) in classifying women veterans with and without posttraumatic stress disorder (PTSD) and other trauma-related outcomes based on functional connectivity using magnetoencephalography (MEG). Here, we extend that line of research to evaluate trauma-specific PTSD neural signatures with MEG in women veterans. Participants completed diagnostic interviews and underwent a task-free MEG scan from which SNI was computed. Thirty-five women veterans were diagnosed with PTSD due to sexual trauma and sixteen with PTSD due to non-sexual trauma. Strength of SNI was compared in women with and without sexual trauma, and linear discriminant analysis was used to classify the brain patterns of women with PTSD due to sexual trauma and non-sexual trauma. Comparison of SNI strength between the two groups revealed widespread hypercorrelation in women with sexual trauma relative to those without sexual trauma. Furthermore, using SNI, the brains of participants were classified as sexual trauma or non-sexual trauma with 100% accuracy. These findings bolster evidence supporting the utility of task-free SNI and suggest that neural signatures of PTSD are trauma-specific.

A Neurobiological Framework for the Therapeutic Potential of Music and Sound Interventions for Post-Traumatic Stress Symptoms in Critical Illness Survivors

Overview: Post traumatic stress disorder (PTSD) has emerged as a severely debilitating psychiatric disorder associated with critical illness. Little progress has been made in the treatment of post-intensive care unit (ICU) PTSD. Aim: To synthesize neurobiological evidence on the pathophysiology of PTSD and the brain areas involved, and to highlight the potential of music to treat post-ICU PTSD. Methods: Critical narrative review to elucidate an evidence-based neurobiological framework to inform the study of music interventions for PTSD post-ICU. Literature searches were performed in PubMed and CINAHL. The Scale for the Assessment of Narrative Review Articles (SANRA) guided reporting. Results: A dysfunctional HPA axis feedback loop, an increased amygdalic response, hippocampal atrophy, and a hypoactive prefrontal cortex contribute to PTSD symptoms. Playing or listening to music can stimulate neurogenesis and neuroplasticity, enhance brain recovery, and normalize stress response. Additionally, evidence supports effectiveness of music to improve coping and emotional regulation, decrease dissociation symptoms, reduce depression and anxiety levels, and overall reduce severity of PTSD symptoms. Conclusions: Despite the lack of music interventions for ICU survivors, music has the potential to help people suffering from PTSD by decreasing amygdala activity, improving hippocampal and prefrontal brain function, and balancing the HPA-axis.

Gene expression in the dorsolateral and ventromedial prefrontal cortices implicates immune-related gene networks in PTSD

Studies evaluating neuroimaging, genetically predicted gene expression, and pre-clinical genetic models of PTSD, have identified PTSD-related abnormalities in the prefrontal cortex (PFC) of the brain, particularly in dorsolateral and ventromedial PFC (dlPFC and vmPFC). In this study, RNA sequencing was used to examine gene expression in the dlPFC and vmPFC using tissue from the VA National PTSD Brain Bank in donors with histories of PTSD with or without depression (dlPFC n = 38, vmPFC n = 35), depression cases without PTSD (n = 32), and psychopathology-free controls (dlPFC n = 24, vmPFC n = 20). Analyses compared PTSD cases to controls. Follow-up analyses contrasted depression cases to controls. Twenty-one genes were differentially expressed in PTSD after strict multiple testing correction. PTSD-associated genes with roles in learning and memory (FOS, NR4A1), immune regulation (CFH, KPNA1) and myelination (MBP, MOBP, ERMN) were identified. PTSD-associated genes partially overlapped depression-associated genes. Co-expression network analyses identified PTSD-associated networks enriched for immune-related genes across the two brain regions. However, the immune-related genes and association patterns were distinct. The immune gene IL1B was significantly associated with PTSD in candidate-gene analysis and was an upstream regulator of PTSD-associated genes in both regions. There was evidence of replication of dlPFC associations in an independent cohort from a recent study, and a strong correlation between the dlPFC PTSD effect sizes for significant genes in the two studies (r = 0.66, p < 2.2 × 10⁻¹⁶). In conclusion, this study identified several novel PTSD-associated genes and brain region specific PTSD-associated immune-related networks.

Experimental trauma rapidly modifies functional connectivity

Traumatic events can produce emotional, cognitive and autonomous physical responses. This may ultimately lead to post-traumatic stress disorder (PTSD), a psychiatric syndrome which requires comprehensive treatment. Trauma exposure alters functional connectivity; however, onset and nature of these changes are unknown. Here, we explore functional connectivity changes at rest directly after experimental trauma exposure. Seventy-three healthy subjects watched either a trauma or a control film. Resting state functional magnetic resonance imaging measurements were conducted before and directly after the film. Seed-based analyses revealed trauma-related changes in functional connectivity, specifically including decreases of connectivity between amygdala and middle temporal gyrus and increases between hippocampus and precuneus. These central effects were accompanied by trauma-related increases in heart rate. Moreover, connectivity between the amygdala and middle temporal gyrus predicted subsequent trauma-related valence. Our results demonstrate rapid functional connectivity changes in memory-related brain regions at rest after experimental trauma, selectively relating to changes in emotions evoked by the trauma manipulation. Results could represent an early predictive biomarker for the development of trauma-related PTSD and thus provide an indication for the need of early targeted preventive interventions.

Neurocircuitry of Contingency Awareness in Pavlovian Fear Conditioning

In Pavlovian fear conditioning, contingency awareness provides an indicator of explicit fear learning. A less studied aspect of fear-based psychopathologies and their treatment, awareness of learned fear is a common cause of distress in persons with such conditions and is a focus of their treatment. The present work is a substudy of a broader fear-conditioning fMRI study. Following fear conditioning, we identified a subset of individuals who did not exhibit explicit awareness of the CS-US contingency. This prompted an exploratory analysis of differences in "aware" versus "unaware" individuals after fear conditioning. Self-reported expectancies of the CS-US contingency obtained immediately following fear conditioning were used to differentiate the two groups. Results corrected for multiple comparisons indicated significantly greater BOLD signal in the bilateral dlPFC, right vmPFC, bilateral vlPFC, left insula, left hippocampus, and bilateral amygdala for the CS+>CS- contrast in the aware group compared with the unaware group (all p values ≤ 0.004). PPI analysis with a left hippocampal seed indicated stronger coupling with the dlPFC and vmPFC in the aware group compared with the unaware group (all p values ≤ 0.002). Our findings add to our current knowledge of the networks involved in explicit learning and awareness of conditioned fear, with important clinical implications.

Dysregulation of inflammation, neurobiology, and cognitive function in PTSD: an integrative review

Compelling evidence from animal and human research suggest a strong link between inflammation and posttraumatic stress disorder (PTSD). Furthermore, recent findings support compromised neurocognitive function as a key feature of PTSD, particularly with deficits in attention and processing speed, executive function, and memory. These cognitive domains are supported by brain structures and neural pathways that are disrupted in PTSD and which are implicated in fear learning and extinction processes. The disruption of these supporting structures potentially results from their interaction with inflammation. Thus, the converging evidence supports a model of inflammatory dysregulation and cognitive dysfunction as combined mechanisms underpinning PTSD symptomatology. In this review, we summarize evidence of dysregulated inflammation in PTSD and further explore how the neurobiological underpinnings of PTSD, in the context of fear learning and extinction acquisition and recall, may interact with inflammation. We then present evidence for cognitive dysfunction in PTSD, highlighting findings from human work. Potential therapeutic approaches utilizing novel pharmacological and behavioral interventions that target inflammation and cognition also are discussed.