High-Resolution Resting-State Functional Connectivity of the Extended Amygdala

Investigating the bed nucleus of the stria terminalis as a predictor of posttraumatic stress disorder in Black Americans and the moderating effects of racial discrimination

Altered functioning of the bed nucleus of the stria terminalis (BNST) may play a critical role in the etiology of posttraumatic stress disorder (PTSD). Chronic stressors such as racial discrimination and lifetime trauma are associated with an increased risk for PTSD, but it is unknown whether they influence the relationship between BNST functioning and PTSD. We investigated acute post-trauma BNST resting-state functional connectivity (rsFC) as a predictor of future PTSD symptoms in Black trauma survivors. We also examined whether racial discrimination and lifetime trauma moderated the relationship between BNST rsFC and PTSD symptoms. Black adults (N = 95; 54.7% female; mean age = 34.04) were recruited from an emergency department after experiencing a traumatic injury (72.6% were motor vehicle accidents). Two-weeks post-injury, participants underwent a resting-state fMRI scan and completed questionnaires evaluating their PTSD symptoms as well as lifetime exposure to racial discrimination and trauma. Six-months post-injury, PTSD symptoms were reassessed. Whole brain seed-to-voxel analyses were conducted to examine BNST rsFC patterns. Greater rsFC between the BNST and the posterior cingulate cortex, precuneus, left angular gyrus, and hippocampus prospectively predicted six-month PTSD symptoms after adjusting for sex, age, education, and baseline PTSD symptoms. Acute BNST rsFC was a stronger predictor of PTSD symptoms in individuals who experienced more racial discrimination and lifetime trauma. Thus, in the acute aftermath of a traumatic event, the BNST could be a key biomarker of risk for PTSD in Black Americans, particularly for individuals with a greater history of racial discrimination or previous trauma exposure.

Understanding the heterogeneity of anxiety using a translational neuroscience approach

Anxiety disorders affect millions of people worldwide and present a challenge in neuroscience research because of their substantial heterogeneity in clinical presentation. While a great deal of progress has been made in understanding the neurobiology of fear and anxiety, these insights have not led to effective treatments. Understanding the relationship between phenotypic heterogeneity and the underlying biology is a critical first step in solving this problem. We show translation, reverse translation, and computational modeling can contribute to a refined, cross-species understanding of fear and anxiety as well as anxiety disorders. More specifically, we outline how animal models can be leveraged to develop testable hypotheses in humans by using targeted, cross-species approaches and ethologically informed behavioral paradigms. We discuss reverse translational approaches that can guide and prioritize animal research in nontraditional research species. Finally, we advocate for the use of computational models to harmonize cross-species and cross-methodology research into anxiety. Together, this translational neuroscience approach will help to bridge the widening gap between how we currently conceptualize and diagnose anxiety disorders, as well as aid in the discovery of better treatments for these conditions.

The PrLGlu→avBNSTGABA circuit rapidly modulates depression-like behaviors in male mice

Depression is a global disease with a high prevalence. Here, we examine the role of the circuit from prelimbic mPFC (PrL) to the anterior ventral bed nucleus of the stria terminalis (avBNST) in depression-like mice through behavioral tests, immunofluorescence, chemogenetics, optogenetics, pharmacology, and fiber photometry. Mice exposed to chronic restraint stress with individual housing displayed depression-like behaviors. Optogenetic or chemogenetic activation of the avBNST-projecting glutamatergic neurons in the PrL had an antidepressant effect. Moreover, we found that α-amino-3-hydroxy-5-methyl-4-isoxazole-propionicacid receptors (AMPARs) play a dominant role in this circuit. Systemic administration of ketamine profoundly alleviated depression-like behaviors in the mice and rapidly rescued the decreased activity in the PrLGlu→avBNSTGABA circuit. Furthermore, the fast-acting effect of ketamine on depressive behaviors was diminished when the circuit was inhibited. To summarize, activating the PrLGlu→avBNSTGABA circuit quickly ameliorated depression-like behaviors. Thus, we propose the PrLGlu→avBNSTGABA circuit as a target for fast regulation of depression.

A pilot study of low-intensity focused ultrasound for treatment-resistant generalized anxiety disorder

OBJECTIVE

This study intended to evaluate a possible therapeutic effect among patients with treatment-refractory generalized anxiety disorder (trGAD) by using transcranial focused ultrasound (tfUS) to modulate amygdalar activity.

METHODS

Twenty-five participants with severe trGAD as outlined in the DSM-V were recruited from Los Angeles neurology and psychiatry clinics. All participants completed eight weekly 10-min tfUS sessions targeting the right amygdala. Functional and structural neuroimaging were used to navigate individual targets. Outcome measures including the Hamilton Anxiety Inventory (HAM-A, primary outcome) and Beck Anxiety Inventory (BAI) were collected at baseline and protocol completion. Upon study completion, participants were asked to report perceived change in clinical status using the Patient Global Impression - Improvement (PGI-I) scale. Data was collected from May 2020 through January 2023.

RESULTS

All participants were able to tolerate treatment without notable side effects. No adverse events were reported. A Wilcoxon Signed-Rank Test was conducted to compare pre- and post-tfUS measures of anxiety. tfUS resulted in a significant decrease in anxiety as measured by the HAM-A (W = -3.69, p < 0.001, pre-post-Δ = -12.64 ± 12.51) and the BAI (W = -3.94, p < 0.001, pre-post-Δ = -12.88 ± 10.42). Sixteen (16) of twenty-five (25) total participants indicated clinically significant benefit on PGI-I scores at completion.

CONCLUSION

This study provides preliminary evidence supporting the safety and efficacy of tfUS as a clinical intervention. These results warrant further investigation of tfUS as a therapeutic intervention for anxiety and other psychiatric and neurological disorders.

CLINICALTRIALS

GOV IDENTIFIER

NCT04250441.

Ultra-high field imaging of the amygdala - A narrative review

The amygdala is an evolutionarily conserved core structure in emotion processing and one of the key regions of interest in affective neuroscience. Results of neuroimaging studies focusing on the amygdala are, however, often heterogeneous since it is composed of functionally and neuroanatomically distinct subnuclei. Fortunately, ultra-high-field imaging offers several advances for amygdala research, most importantly more accurate representation of functional and structural properties of subnuclei and their connectivity. Most clinical studies using ultra-high-field imaging focused on major depression, suggesting either overall rightward amygdala atrophy or distinct bilateral patterns of subnuclear atrophy and hypertrophy. Other pathologies are only sparsely covered. Connectivity analyses identified widespread networks for learning and memory, stimulus processing, cognition, and social processes. They provide evidence for distinct roles of the central, basal, and basolateral nucleus, and the extended amygdala in fear and emotion processing. Amid largely sparse and ambiguous evidence, we propose theoretical and methodological considerations that will guide ultra-high-field imaging in comprehensive investigations to help disentangle the ambiguity of the amygdala's function, structure, connectivity, and clinical relevance.

Unbalanced functional connectivity at rest affects the ERP correlates of affective prediction in high intolerance of uncertainty individuals: A high density EEG investigation

In a recent study we outlined the link between Intolerance of Uncertainty (IU) and the neural correlates of affective predictions, as constructed by the brain (generation stage) to prepare to relevant stimuli (implementation stage), and update predictive models according to incoming stimuli (updating stage). In this study we further explored whether the brain's functional organization at rest can modulate neural activity elicited within an emotional S1-S2 paradigm as a function of IU and uncertainty of S1-S2 contingencies. We computed resting state functional connectivity (RS-FC) from a 3-min resting period recorded with high density EEG, and we tested whether RS graph theory nodal measures (i.e., strength, clustering coefficient, betweenness centrality) predicted in-task ERP modulation as a function of IU. We found that RS-FC differently predicted in-task ERPs within the generation and updating stages. Higher IU levels were associated to altered RS-FC patterns within both domain-specific (i.e., right superior temporal sulcus) and domain-general regions (i.e., right orbitofrontal cortex), predictive of a reduced modulation of in-task ERPs in the generation and updating stages. This is presumably ascribable to an unbalancing between synchronization and integration within these regions, which may disrupt the exchange of information between top-down and bottom-up pathways. This altered RS-FC pattern may in turn result in the construction of less efficient affective predictions and a reduced ability to deal with contextual uncertainty in individuals high in IU.

Cortico-subcortical interactions in overlapping communities of edge functional connectivity

Both cortical and subcortical regions can be functionally organized into networks. Regions of the basal ganglia are extensively interconnected with the cortex via reciprocal connections that relay and modulate cortical function. Here we employ an edge-centric approach, which computes co-fluctuations among region pairs in a network to investigate the role and interaction of subcortical regions with cortical systems. By clustering edges into communities, we show that cortical systems and subcortical regions couple via multiple edge communities, with hippocampus and amygdala having a distinct pattern from striatum and thalamus. We show that the edge community structure of cortical networks is highly similar to one obtained from cortical nodes when the subcortex is present in the network. Additionally, we show that the edge community profile of both cortical and subcortical nodes can be estimates solely from cortico-subcortical interactions. Finally, we used a motif analysis focusing on edge community triads where a subcortical region coupled to two cortical regions and found that two community triads where one community couples the subcortex to the cortex were overrepresented. In summary, our results show organized coupling of the subcortex to the cortex that may play a role in cortical organization of primary sensorimotor/attention and heteromodal systems and puts forth the motif analysis of edge community triads as a promising method for investigation of communication patterns in networks.

Volume of Amygdala Subregions and Clinical Manifestations in Patients With First-Episode, Drug-Naïve Major Depression

We examined amygdala subregion volumes in patients with a first episode of major depression (MD) and in healthy subjects. Covariate-adjusted linear regression was performed to compare the MD and healthy groups, and adjustments for age, gender, and total estimated intracranial volume showed no differences in amygdala subregion volumes between the healthy and MD groups. Within the MD group, we examined the association between amygdala subregion volume and the 17-item Hamilton Rating Scale for Depression (HAMD) score and the HAMD subscale score, and found no association in the left amygdala. In the right amygdala, however, there was an inverse linear association between the HAMD total and the HAMD core and lateral nucleus and anterior-amygdaloid-regions. Furthermore, an inverse linear association was seen between the HAMD psychic and the lateral nucleus, anterior-amygdaloid-regions, transition, and whole amygdala. The findings of this study suggest that the severity of MD and some symptoms of MD are associated with right amygdala volume. There have been few reports on the relationship between MD and amygdala subregional volume, and further research is needed to accumulate more data for further validation.

Ongoing habenular activity is driven by forebrain networks and modulated by olfactory stimuli

Ongoing neural activity, which represents internal brain states, is constantly modulated by the sensory information that is generated by the environment. In this study, we show that the habenular circuits act as a major brain hub integrating the structured ongoing activity of the limbic forebrain circuitry and the olfactory information. We demonstrate that ancestral homologs of amygdala and hippocampus in zebrafish forebrain are the major drivers of ongoing habenular activity. We also reveal that odor stimuli can modulate the activity of specific habenular neurons that are driven by this forebrain circuitry. Our results highlight a major role for the olfactory system in regulating the ongoing activity of the habenula and the forebrain, thereby altering brain's internal states.

Structural and resting state functional connectivity beyond the cortex

Mapping the structural and functional connectivity of the central nervous system has become a key area within neuroimaging research. While detailed network structures across the entire brain have been probed using animal models, non-invasive neuroimaging in humans has thus far been dominated by cortical investigations. Beyond the cortex, subcortical nuclei have traditionally been less accessible due to their smaller size and greater distance from radio frequency coils. However, major neuroimaging developments now provide improved signal and the resolution required to study these structures. Here, we present an overview of the connectivity between the amygdala, brainstem, cerebellum, spinal cord and the rest of the brain. While limitations to their imaging and analyses remain, we also provide some recommendations and considerations for mapping brain connectivity beyond the cortex.

A 7-Tesla MRI Study of the Periaqueductal Grey: Resting State and Task Activation Under Threat

The periaqueductal grey (PAG) is a region of the midbrain implicated in a variety of behaviors including defensive responses to threat. Despite the wealth of knowledge pertaining to the differential functional roles of the PAG columns in nonhuman and human research, the basic functional connectivity of the PAG at rest has not been well characterized. Therefore, the current study utilized 7-Tesla MRI to characterize PAG functional connectivity at rest and task activation under uncertain threat. A sample of 53 neurologically healthy undergraduate participants (Mage=22.2, SDage=3.62) underwent structural and resting state functional MRI scans. Supporting previous work, voxel-wise analyses showed the PAG is functionally connected to emotion regulation and fear networks. Comparison of functional connectivity of PAG columns did not reveal any significant differences. Thirty-five participants from the same sample also completed an uncertain threat task with blocks of 3 conditions-No shock, Predictable shock, and Unpredictable shock. There were no robust activity differences within the PAG columns or the whole PAG across conditions, though there was differential activity at the voxel level in the PAG and in other regions theoretically relevant to uncertain threat. Results of this study elucidate PAG connectivity at rest and activation in response to uncertain threat.

A narrative review of emotion regulation process in stress and recovery phases

The difficulty in studying the relationship between stress and emotional regulation is due to the need to contemplate a dynamic perspective that analyzes the moderating role of stress. In fact, stress involves different phases or stages, and the neurocognitive processes involved in emotion regulation differ significantly between these phases. The period of anticipation of stressful events can be fundamental to understand the process of stress regulation; however, surprisingly few works have analyzed the differential activation of brain networks involved in cognitive regulation during the phases of stress and recovery. Taking this into consideration, within this study we propose to analyze in an integrated way the psychological and neurobiological processes during the phase of stress and recovery, with the aim of improving our understanding of the mechanisms that underlie successful and unsuccessful stress regulation. We consider that from the present review we contribute to achieve a better understanding of the mechanisms underlying successful and unsuccessful stress regulation would contribute to the improvement of prevention and treatment interventions for mental disorders.

Neural substrates of human fear generalization: A 7T-fMRI investigation

Fear generalization - the tendency to interpret ambiguous stimuli as threatening due to perceptual similarity to a learned threat - is an adaptive process. Overgeneralization, however, is maladaptive and has been implicated in a number of anxiety disorders. Neuroimaging research has indicated several regions sensitive to effects of generalization, including regions involved in fear excitation (e.g., amygdala, insula) and inhibition (e.g., ventromedial prefrontal cortex). Research has suggested several other small brain regions may play an important role in this process (e.g., hippocampal subfields, bed nucleus of the stria terminalis [BNST], habenula), but, to date, these regions have not been examined during fear generalization due to limited spatial resolution of standard human neuroimaging. To this end, we utilized the high spatial resolution of 7T fMRI to characterize the neural circuits involved in threat discrimination and generalization. Additionally, we examined potential modulating effects of trait anxiety and intolerance of uncertainty on neural activation during threat generalization. In a sample of 31 healthy undergraduate students, significant positive generalization effects (i.e., greater activation for stimuli with increasing perceptual similarity to a learned threat cue) were observed in the visual cortex, thalamus, habenula and BNST, while negative generalization effects were observed in the dentate gyrus, CA1, and CA3. Associations with individual differences were underpowered, though preliminary findings suggested greater generalization in the insula and primary somatosensory cortex may be correlated with self-reported anxiety. Overall, findings largely support previous neuroimaging work on fear generalization and provide additional insight into the contributions of several previously unexplored brain regions.

Extended-amygdala intrinsic functional connectivity networks: A population study

Pre-clinical and human neuroimaging research implicates the extended-amygdala (ExtA) (including the bed nucleus of the stria terminalis [BST] and central nucleus of the amygdala [CeA]) in networks mediating negative emotional states associated with stress and substance-use behaviours. The extent to which individual ExtA structures form a functionally integrated unit is controversial. We utilised a large sample (n > 1,000 healthy young adult humans) to compare the intrinsic functional connectivity networks (ICNs) of the BST and CeA using task-free functional magnetic resonance imaging (fMRI) data from the Human Connectome Project. We assessed whether inter-individual differences within these ICNs were related to two principal components representing negative disposition and alcohol use. Building on recent primate evidence, we tested whether within BST-CeA intrinsic functional connectivity (iFC) was heritable and further examined co-heritability with our principal components. We demonstrate the BST and CeA to have discrete, but largely overlapping ICNs similar to previous findings. We found no evidence that within BST-CeA iFC was heritable; however, post hoc analyses found significant BST iFC heritability with the broader superficial and centromedial amygdala regions. There were no significant correlations or co-heritability associations with our principal components either across the ICNs or for specific BST-Amygdala iFC. Possible differences in phenotype associations across task-free, task-based, and clinical fMRI are discussed, along with suggestions for more causal investigative paradigms that make use of the now well-established ExtA ICNs.

Effective connectivity between bed nucleus of the stria terminalis and amygdala: Reproducibility and relation to anxiety

In a previous study, we investigated the resting‐state fMRI effective connectivity (EC) between the bed nucleus of the stria terminalis (BNST) and the laterobasal (LB), centromedial (CM), and superficial (SF) amygdala. We found strong negative EC from all amygdala nuclei to the BNST, while the BNST showed positive EC to the amygdala. However, the validity of these findings remains unclear, since a reproduction in different samples has not been done. Moreover, the association of EC with measures of anxiety offers deeper insight, due to the known role of the BNST and amygdala in fear and anxiety. Here, we aimed to reproduce our previous results in three additional samples. We used spectral Dynamic Causal Modeling to estimate the EC between the BNST, the LB, CM, and SF, and its association with two measures of self‐reported anxiety. Our results revealed consistency over samples with regard to the negative EC from the amygdala nuclei to the BNST, while the positive EC from BNST to the amygdala was also found, but weaker and more heterogenic. Moreover, we found the BNST‐BNST EC showing a positive and the CM‐BNST EC, showing a negative association with anxiety. Our study suggests a reproducible pattern of negative EC from the amygdala to the BNST along with weaker positive EC from the BNST to the amygdala. Moreover, less BNST self‐inhibition and more inhibitory influence from the CM to the BNST seems to be a pattern of EC that is related to higher anxiety.

Resting State Cortico-Limbic Functional Connectivity and Dispositional Use of Emotion Regulation Strategies: A Replication and Extension Study

Neuroimaging functional connectivity analyses have shown that the negative coupling between the amygdala and cortical regions is linked to better emotion regulation (ER) in experimental task settings. However, less is known about the neural correlates of ER traits or dispositions. The present study aimed to: (1) replicate the findings of differential cortico-limbic coupling during resting-state depending on the dispositional use of emotion regulation strategies. Furthermore, the study aimed to: (2) extend prior findings by examining whether differences in cortico-limbic coupling during resting-state predict experiential and neuronal ER success in a standard ER task. To this end, N = 107 healthy adults completed the Emotion Regulation Questionnaire (ERQ), underwent an 8-min resting-state fMRI acquisition, and completed a reappraisal task during fMRI. Functional connectivity maps of basolateral and centromedial amygdala nuclei were estimated with a seed-based approach regarding associations with regions of the prefrontal cortex and were then correlated with ERQ scores as well as experiential and neuronal ER success. All hypotheses and the analysis plan are preregistered at https://osf.io/8wsgu. Opposed to prior findings, we were not able to replicate a correlation of dispositional ER strategy use with functional connectivity between the amygdala and PFC regions (p > 0.05, FWE-corrected). Furthermore, there was no association of experiential and neuronal reappraisal success with functional connectivity between amygdala and insula as well as PFC (p > 0.05, FWE-corrected). The present preregistered study calls into question the reported association between individual differences in resting-state cortico-limbic connectivity and dispositional use of ER strategies. However, ongoing advances in functional brain imaging and distributed network approaches may leverage the identification of reliable functional connectivity patterns that underlie successful emotion regulation.