Resting-state functional connectivity in combat veterans suffering from impulsive aggression

Trait Aggression is Reflected by a Lower Temporal Stability of EEG Resting Networks

Trait aggression can lead to catastrophic consequences for individuals and society. However, it remains unclear how aggressive people differ from others regarding basic, task-independent brain characteristics. We used EEG microstate analysis to investigate how the temporal organization of neural resting networks might help explain inter-individual differences in aggression. Microstates represent whole-brain networks, which are stable for short timeframes (40-120 ms) before quickly transitioning into other microstate types. Recent research demonstrates that the general temporal stability of microstates across types predicts higher levels of self-control and inhibitory control, and lower levels of risk-taking preferences. Given that these outcomes are inversely related to aggression, we investigated whether microstate stability at rest would predict lower levels of trait aggression. As males show higher levels of aggression than females, and males and females express aggression differently, we also tested for possible gender-differences. As hypothesized, people with higher levels of trait aggression showed lower microstate stability. This effect was moderated by gender, with men showing stronger associations compared to women. These findings support the notion that temporal dynamics of sub-second resting networks predict complex human traits. Furthermore, they provide initial indications of gender-differences in the functional significance of EEG microstates.

The role of intimate partner violence perpetrators' resting state functional connectivity in treatment compliance and recidivism

To expand the scientific literature on how resting state functional connectivity (rsFC) magnetic resonance imaging (MRI) (or the measurement of the strength of the coactivation of two brain regions over a sustained period of time) can be used to explain treatment compliance and recidivism among intimate partner violence (IPV) perpetrators. Therefore, our first aim was to assess whether men convicted of IPV (n = 53) presented different rsFC patterns from a control group of non-violent (n = 47) men. We also analyzed if the rsFC of IPV perpetrators before staring the intervention program could explain treatment compliance and recidivism one year after the intervention ended. The rsFC was measured by applying a whole brain analysis during a resting period, which lasted 45 min. IPV perpetrators showed higher rsFC in the occipital brain areas compared to controls. Furthermore, there was a positive association between the occipital pole (OP) and temporal lobes (ITG) and a negative association between the occipital (e.g., occipital fusiform gyrus, visual network) and both the parietal lobe regions (e.g., supramarginal gyrus, parietal operculum cortex, lingual gyrus) and the putamen in IPV perpetrators. This pattern was the opposite in the control group. The positive association between many of these occipital regions and the parietal, frontal, and temporal regions explained treatment compliance. Conversely, treatment compliance was also explained by a reduced rsFC between the rostral prefrontal cortex and the frontal gyrus and both the occipital and temporal gyrus, and between the temporal and the occipital and cerebellum areas and the sensorimotor superior networks. Last, the enhanced rsFC between the occipital regions and both the cerebellum and temporal gyrus predicted recidivism. Our results highlight that there are specific rsFC patterns that can distinguish IPV perpetrators from controls. These rsFC patterns could be useful to explain treatment compliance and recidivism among IPV perpetrators.

Neurobiology of Aggression-Review of Recent Findings and Relationship with Alcohol and Trauma

Aggression can be conceptualized as any behavior, physical or verbal, that involves attacking another person or animal with the intent of causing harm, pain or injury. Because of its high prevalence worldwide, aggression has remained a central clinical and public safety issue. Aggression can be caused by several risk factors, including biological and psychological, such as genetics and mental health disorders, and socioeconomic such as education, employment, financial status, and neighborhood. Research over the past few decades has also proposed a link between alcohol consumption and aggressive behaviors. Alcohol consumption can escalate aggressive behavior in humans, often leading to domestic violence or serious crimes. Converging lines of evidence have also shown that trauma and posttraumatic stress disorder (PTSD) could have a tremendous impact on behavior associated with both alcohol use problems and violence. However, although the link between trauma, alcohol, and aggression is well documented, the underlying neurobiological mechanisms and their impact on behavior have not been properly discussed. This article provides an overview of recent advances in understanding the translational neurobiological basis of aggression and its intricate links to alcoholism and trauma, focusing on behavior. It does so by shedding light from several perspectives, including in vivo imaging, genes, receptors, and neurotransmitters and their influence on human and animal behavior.

Lower cerebello-cortical functional connectivity in veterans with reactive aggression symptoms: A pilot study

A significant number of veterans experience irritability and aggression symptoms as a result of being exposed to extremely stressful and life-threatening situations. In addition to the well-established involvement of the brain's cortico-subcortical circuit in aggression-related behaviours, a role of the deep cerebellar nuclei (DCN) in reactive aggression has been suggested. In the present study, seed-based resting-state functional connectivity between the DCN and cortico-subcortical areas was explored in veterans with and without reactive aggression symptoms. Nineteen male veterans with reactive aggression symptoms and twenty-two control veterans without reactive aggression symptoms underwent 3T resting-state functional MRI scans. Region-of-interest (ROI) analyses that included the amygdala, hypothalamus and periaqueductal grey as ROIs did not yield significant group-related differences in resting-state functional connectivity with the DCN. However, exploratory whole-brain analysis showed that veterans with reactive aggression symptoms exhibited lower functional connectivity between the DCN and the orbitofrontal cortex compared to control veterans. Our findings provide preliminary evidence for the possible involvement of a cerebello-prefrontal pathway in reactive aggression in male veterans.

Amygdala connectivity and aggression

Neurobiological models propose that reactive aggression is predicated on impairments in amygdala-prefrontal connectivity that subserves moral decision-making and emotion regulation. The amygdala is a key component within this neural network that modulates reactive aggression. We provide a review of amygdala dysfunctional brain networks leading to reactive aggressive behavior. We elaborate on key concepts, focusing on moral decision-making and emotion regulation in a developmental context, and brain network connectivity factors relating to amygdala (dys)function-factors which we suggest predispose to reactive aggression. We additionally discuss insights into the latest treatment interventions, providing the utilization of the scientific findings for practice.

Problematic Anger in the Military: Focusing on the Forgotten Emotion

PURPOSE OF REVIEW

Problematic anger is common in veteran and military populations, yet understudied relative to other mental health difficulties. However, in recent years, more clinical and research attention has been turned to problematic anger. This paper highlights important new findings in the epidemiology, course, and neurobiology of anger, the associations of anger with other mental health problems and risk, and next steps for research and practice.

RECENT FINDINGS

In longitudinal research, findings show that problematic anger changes over the life course of military members and veterans, and that deployment increases the likelihood of problematic levels of anger. Problematic anger is related to a range of mental health issues, most perniciously aggression and suicidality. Promising new assessment and treatment approaches are emerging, including innovations that leverage digital technology. Key areas of research include advancing assessment of problematic anger to identify patterns of heterogeneity, as well as advancing the evidence base for anger treatments. Recommended progress in clinical practice include conducting routine assessment of problematic anger in veteran and military populations, developing prevention and early intervention for at risk individuals, and optimizing the timing of interventions throughout the military lifecycle.

Functional connectivity of amygdala subregions predicts vulnerability to depression following the COVID-19 pandemic

BACKGROUND

The amygdala is vital in processing psychological stress and predicting vulnerability or resilience to stress-related disorders. This study aimed to build the link between functional magnetic resonance imaging data obtained before the stress event and the subsequent stress-related depressive symptoms.

METHODS

Neuroimaging data obtained before the coronavirus disease 2019 pandemic from 39 patients with major depressive disorder (MDD) and 61 health controls (HCs) were used in this study. The participants were divided retrospectively into four groups in accordance with the severity of depressive symptoms during the pandemic: remitted patients, non-remitted patients, depressed HCs (HCd) and non-depressed HCs (HCnd). Seed-based resting-state functional connectivity (rsFC) analyses of the amygdala and its subregions, including the centromedial (CM), the basolateral and the superficial (SF), were performed.

RESULTS

Vulnerability to depression was suggested by decreased rsFC between the left CM amygdala and the bilateral lingual gyrus in the HCd group compared with the HCnd group, and decreased rsFC of the left CM or right SF amygdala with the precuneus and the postcentral gyrus in the HCd group compared with patients with MDD. No evidence supported the rsFC of the amygdala or its subregions as a biomarker for the resilience of patients with MDD to stress under antidepressant treatment.

LIMITATIONS

Smaller sample size and no longitudinal neuroimaging data.

CONCLUSIONS

Our findings suggested that the rsFC of amygdala subregions may represent a neurobiological marker of vulnerability to depression following stress.

Structural covariance of amygdala subregions is associated with trait aggression and endogenous testosterone in healthy individuals

Many studies point toward volume reductions in the amygdala as a potential neurostructural marker for trait aggression. However, most of these findings stem from clinical samples, rendering unclear whether the findings generalize to non-clinical populations. Furthermore, the notion of neural networks suggests that interregional correlations in gray matter volume (i.e., structural covariance) can explain individual differences in aggressive behavior beyond local univariate associations. Here, we tested whether structural covariance between amygdala subregions and the rest of the brain is associated with self-reported aggression in a large sample of healthy young students (n = 263; 49% women). Salivary testosterone concentrations were measured for a subset of n = 40 male and n = 36 female subjects, allowing us to investigate the influence of endogenous testosterone on structural covariance. Aggressive individuals showed enhanced covariance between left superficial amygdala (SFA) and left dorsal anterior insula (dAI), but lower covariance between right laterobasal amygdala (LBA) and right dorsolateral prefrontal cortex (dlPFC). These structural patterns overlap with functional networks involved in the genesis and regulation of aggressive behavior, respectively. With increasing endogenous testosterone, we observed stronger structural covariance between right centromedial amygdala (CMA) and right medial prefrontal cortex in men and between left CMA and bilateral orbitofrontal cortex in women. These results speak for structural covariance of amygdala subregions as a robust correlate of trait aggression in healthy individuals. Moreover, regions that showed structural covariance with the amygdala modulated by either testosterone or aggression did not overlap, suggesting a complex role of testosterone in human social behavior beyond facilitating aggressiveness.

Increased amygdala and decreased frontolimbic r esting- s tate functional connectivity in children with aggressive behavior

Childhood maladaptive aggression is associated with disrupted functional connectivity within amygdala-prefrontal circuitry. In this study, neural correlates of childhood aggression were probed using the intrinsic connectivity distribution, a voxel-wise metric of global resting-state brain connectivity. This sample included 38 children with aggressive behavior (26 boys, 12 girls) ages 8-16 years and 21 healthy controls (14 boys, 6 girls) matched for age and IQ. Functional MRI data were acquired during resting state, and differential patterns of intrinsic functional connectivity were tested in a priori regions of interest implicated in the pathophysiology of aggressive behavior. Next, correlational analyses tested for associations between functional connectivity and severity of aggression measured by the Reactive-Proactive Aggression Questionnaire in children with aggression. Children with aggressive behavior showed increased global connectivity in the bilateral amygdala relative to controls. Greater severity of aggressive behavior was associated with decreasing global connectivity in the dorsal anterior cingulate and ventromedial prefrontal cortex. Follow-up seed analysis revealed that aggression was also positively correlated with left amygdala connectivity with the dorsal anterior cingulate, ventromedial and dorsolateral prefrontal cortical regions. These results highlight the potential role of connectivity of the amygdala and medial prefrontal and anterior cingulate cortices in modulating the severity of aggressive behavior in treatment-seeking children.

The Modulatory Role of Serotonin on Human Impulsive Aggression

The hypothesis of chronically low brain serotonin levels as pathophysiologically linked to impulsive aggression has been around for several decades. Whereas the theory was initially based on indirect methods to probe serotonin function, our understanding of the neural mechanisms involved in impulsive aggression has progressed with recent advances in neuroimaging. The review integrates evidence based on data from several neuroimaging domains in humans. In vivo molecular neuroimaging findings demonstrate associations between impulsive aggression and high serotonin 1B and serotonin 4 receptor binding, high serotonin transporter levels, and low monoamine oxidase A levels, suggesting that low interstitial serotonin levels are a neurobiological risk factor for impulsive aggressive behavior. Imaging genetics suggests that serotonergic-related genetic polymorphisms associate with antisocial behavior, and some evidence indicates that the low-expressing monoamine oxidase A genotype specifically predisposes to impulsive aggression, which may be mediated by effects on corticolimbic function. Interventions that (presumably) alter serotonin levels have effects on brain activity within brain regions involved in impulsive aggression, notably the amygdala, dorsal striatum, anterior cingulate, insula, and prefrontal cortex. Based on these findings, we propose a model for the modulatory role of serotonin in impulsive aggression. Future studies should ensure that clinical features unique for impulsive aggression are appropriately assessed, and we propose investigations of knowledge gaps that can help confirm, refute, or modify our proposed model of impulsive aggression.

Neural correlates of anger expression in patients with PTSD

Anger is a common and debilitating symptom of post-traumatic stress disorder (PTSD). Although studies have identified brain circuits underlying anger experience and expression in healthy individuals, how these circuits interact with trauma remains unclear. Here, we performed the first study examining the neural correlates of anger in patients with PTSD. Using a data-driven approach with resting-state fMRI, we identified two prefrontal regions whose overall functional connectivity was inversely associated with anger: the left anterior middle frontal gyrus (aMFG) and the right orbitofrontal cortex (OFC). We then used concurrent TMS-EEG to target the left aMFG parcel previously identified through fMRI, measuring its cortical excitability and causal connectivity to downstream areas. We found that low-anger PTSD patients exhibited enhanced excitability in the left aMFG and enhanced causal connectivity between this region and visual areas. Together, our results suggest that left aMFG activity may confer protection against the development of anger, and therefore may be an intriguing target for circuit-based interventions for anger in PTSD.

Voxel-based morphometry and cortical thickness in combat veterans suffering from impulsive aggression

BACKGROUND

Problems with impulsive aggression occur in many forms of psychiatric dysfunction, and are a common complaint among combat veterans. The present study sought to examine the neuroanatomical correlates of combat-related impulsive aggression.

METHODS

T1-weighted magnetic resonance images were acquired from 29 male veterans with impulsive aggression and 30 non-aggressive combat controls. Subcortical volumetry was conducted with the amygdala and hippocampus and their main constituent subdivisions as regions-of-interest (ROIs) (basolateral, centromedial amygdala; head, body, tail of hippocampus). Cortical thickness measurements were extracted for the dorsolateral prefrontal cortex, orbitofrontal cortex, and anterior cingulate cortex. Within-group correlations with psychometric measures were also explored.

RESULTS

No significant group differences in cortical thickness or subcortical grey matter volumes were observed for any of the ROIs. Also, no significant correlations with any of the psychometric measures were recorded. Exploratory whole-brain analysis of cortical thickness revealed a significant group × anxiety interaction effect in a cluster located in the left lingual gyrus.

CONCLUSIONS

The current findings indicate that problems with impulsive aggression may not be directly associated with alterations in cortical thickness or amygdalar/hippocampal (sub)volumes. The observed interplay between impulsive aggression problems and anxiety-related symptoms is consistent with prior work showing the two phenomena may share the same underlying (neural) mechanisms.

Longitudinal Changes After Amygdala Surgery for Intractable Aggressive Behavior: Clinical, Imaging Genetics, and Deformation-Based Morphometry Study-A Case Series

BACKGROUND

Intractable aggressive behavior (iAB) is a devastating behavioral disorder that may affect psychiatric patients. These patients have reduced quality of life, are more challenging to treat as they impose a high caregiver burden and require specialized care. Neuromodulatory interventions targeting the amygdala, a key hub in the circuitry of aggressive behavior (AB), may provide symptom alleviation.

OBJECTIVE

To Report clinical and imaging findings from a case series of iAB patients treated with bilateral amygdala ablation.

METHODS

This series included 4 cases (3 males, 19-32 years old) who underwent bilateral amygdala radiofrequency ablation for iAB hallmarked by life-threatening self-injury and social aggression. Pre- and postassessments involved full clinical, psychiatric, and neurosurgical evaluations, including scales quantifying AB, general agitation, quality of life, and magnetic resonance imaging (MRI).

RESULTS

Postsurgery assessments revealed decreased aggression and agitation and improved quality of life. AB was correlated with testosterone levels and testosterone/cortisol ratio in males. No clinically significant side effects were observed. Imaging analyses showed preoperative amygdala volumes within normal populational range and confirmed lesion locations. The reductions in aggressive symptoms were accompanied by significant postsurgical volumetric reductions in brain areas classically associated with AB and increases in regions related to somatosensation. The local volumetric reductions are found in areas that in a normal brain show high expression levels of genes related to AB (eg, aminergic transmission) using gene expression data provided by the Allen brain atlas.

CONCLUSION

These findings provide new insight into the whole brain neurocircuitry of aggression and suggest a role of altered somatosensation and possible novel neuromodulation targets.

Cingulum White Matter Integrity as a Mediator Between Harm Avoidance and Hostility

As a textbook manifestation of an aggressive attitude, hostility can pose a serious threat to both an individual's life and the security of society at large. Past evidence suggests that some anxiety-related traits may be more prone to giving rise to hostility. However, many aspects of hostility, such as, determining the susceptible temperament for hostility, the neural basis of hostility, and the underlying mechanisms through which having a susceptible temperament generates hostility in a healthy brain, remain unclear. In this study, we sought to delve into these questions by assessing temperament and brain white matter integrity using self-report questionnaires and diffusion tensor imaging in a sizable sample of healthy adults (n = 357). First, we investigated the relationship between hostility and the four temperaments of the Cloninger model. Then, we investigated which white matter tracts were significantly correlated with hostility using a whole-brain analysis. Finally, we used a mediation analysis to explore the tripartite relationship between vulnerability temperament, the fractional anisotropy (FA) value of the white matter, and hostility. Our results suggest that a harm avoidance temperament may be susceptible to hostility and that the cingulum may be a key white matter region responsible for hostility. Based on these results, we developed a temperament-brain-attitude pathway showing how harm avoidance temperament could affect the brain and ultimately lead to hostility.

Neurobiological evidence of sexual dimorphism in limbic circuitry of US Veterans

BACKGROUND

Female Veterans are an increasing patient population in the Department of Veterans Affairs and may have distinct clinical and neurobiological features compared to males.

METHODS

Nineteen female and 19 male Veterans who met diagnostic criteria for depression/posttraumatic stress disorder (MDD/PTSD) completed diagnostic interviews, symptom measures, and resting-state neuroimaging. Participants completed clinical measures of mood and aggression in addition to magnetic resonance imaging on a 3.0 Tesla Siemens scanner.

RESULTS

Females showed increased functional connectivity between the left and right basolateral amygdala (BLA) and the left and right cerebellar and occipital lobes. Sex differences also were evident in the relationship between affective and clinical symptoms with BLA connectivity. Females showed a correlation between revenge planning and decreased connectivity between the left BLA and left occipital lobe and also a correlation between aggression and decreased connectivity between the right BLA and right mid cingulate, right and left medial frontal lobe, and right frontal lobe. Males evidenced a relationship between increased depressive symptoms and increased connectivity between the left BLA and right and left occipital lobe, left calcarine, and other areas associated with visual memory and processing, and interpretation of sensory information. Additionally, males reported higher levels of physical aggression and revenge planning compared to females.

LIMITATIONS

This study included neuroimaging and self-report clinical measures. Further studies will benefit from multimodal measures, including behavioral measures of aggression.

CONCLUSIONS

Results suggest that male Veterans report more aggression than females and symptoms of aggression and mood are differentially related to BLA connectivity by sex.

Multi-voxel pattern analysis of amygdala functional connectivity at rest predicts variability in posttraumatic stress severity

INTRODUCTION

Resting state functional magnetic resonance imaging (rsfMRI) studies demonstrate that individuals with posttraumatic stress disorder (PTSD) exhibit atypical functional connectivity (FC) between the amygdala, involved in the generation of emotion, and regions responsible for emotional appraisal (e.g., insula, orbitofrontal cortex [OFC]) and regulation (prefrontal cortex [PFC], anterior cingulate cortex). Consequently, atypical amygdala FC within an emotional processing and regulation network may be a defining feature of PTSD, although altered FC does not seem constrained to one brain region. Instead, altered amygdala FC involves a large, distributed brain network in those with PTSD. The present study used a machine-learning data-driven approach, multi-voxel pattern analysis (MVPA), to predict PTSD severity based on whole-brain patterns of amygdala FC.

METHODS

Trauma-exposed adults (N = 90) completed the PTSD Checklist-Civilian Version to assess symptoms and a 5-min rsfMRI. Whole-brain FC values to bilateral amygdala were extracted and used in a relevance vector regression analysis with a leave-one-out approach for cross-validation with permutation testing (1,000) to obtain significance values.

RESULTS

Results demonstrated that amygdala FC predicted PCL-C scores with statistically significant accuracy (r = .46, p = .001; mean sum of squares = 130.46, p = .001; R²  = 0.21, p = .001). Prediction was based on whole-brain amygdala FC, although regions that informed prediction (top 10%) included the OFC, amygdala, and dorsolateral PFC.

CONCLUSION

Findings demonstrate the utility of MVPA based on amygdala FC to predict individual severity of PTSD symptoms and that amygdala FC within a fear acquisition and regulation network contributed to accurate prediction.

Effects of exogenous testosterone application on network connectivity within emotion regulation systems

Studies with steroid hormones underlined the vital role of testosterone on social-emotional processing. However, there is still a lack of studies investigating whether testosterone modulates network connectivity during resting-state. Here, we tested how the exogenous application of testosterone would affect functional connectivity between regions implicated in emotion regulation. In total, 96 male participants underwent resting-state fMRI scanning. Before the measurement, half of the subjects received 5 g Testim^TM gel (containing 50 mg testosterone) and the other half a corresponding amount of placebo gel. Seeds for the connectivity analysis were meta-analytically defined. First, all regions associated with emotion regulation were chosen via Neurosynth (data driven). Among those, specific seeds were selected and categorized based on the neural model of emotion regulation by Etkin and colleagues (Etkin et al., 2015) (theory-guided). Resting-state connectivity analysis revealed decreased connectivity between the right DLPFC and the right amygdala as well as between the VMPFC and the left IPL for the testosterone group compared to the placebo group. A complementary dynamic causal modeling (DCM) analysis on findings from the resting-state connectivity analysis underlined a bidirectional coupling which was decreased close to zero by testosterone administration. Our results demonstrate that testosterone administration disrupts resting-state connectivity within fronto-subcortical and fronto-parietal circuits. The findings suggest that even without a specific task (e.g. challenge, reward processing) testosterone modulates brain networks important for social-emotional processing.

Anger provocation increases limbic and decreases medial prefrontal cortex connectivity with the left amygdala in reactive aggressive violent offenders

Neurobiological models propose reactive aggression as a failure in emotion regulation, caused by an imbalance between prefrontal cortical control and excessive bottom-up signals of negative affect by limbic regions, including the amygdala. Therefore, we hypothesize a negative correlation between PFC and amygdala activity (pre/post resting-state scans) in violent offenders. In this study resting-state fMRI was administered before and after an emotion (anger and happiness) provocation or engagement task within 18 male violent offenders scoring high on reactive aggression, and 18 male non-offender controls. Research in emotional pre/post resting-state showed altered connectivity by task performance. Therefore, bilateral amygdala region of interest (ROI) whole brain functional connectivity analysis tested dynamic change differences between pre and post resting-state connectivity between groups. Self-reported anger showed a positive significant relationship with medial prefrontal cortex activity in the pre-task scan and significantly increased during the emotion task in both the violent and control group. Imaging results showed a significant decrease in amygdala – medial prefrontal functional connectivity in the violent offenders and an increase in the non-offender controls after the emotion task. The opposite pattern was found for amygdala connectivity with the (para) limbic regions: violent offenders showed increased connectivity and non-offender controls showed decreased connectivity. The present results indicate that reactive aggression might stem from a focus on emotion processing, as indicated by an increase in limbic functional connectivity. The combination of a focus on emotion, along with a lack of medial prefrontal cortex regulation, has the potential to grow out of control e.g. in reactive aggression.

Regions of white matter abnormalities in the arcuate fasciculus in veterans with anger and aggression problems

Aggression after military deployment is a common occurrence in veterans. Neurobiological research has shown that aggression is associated with a dysfunction in a network connecting brain regions implicated in threat processing and emotion regulation. However, aggression may also be related to deficits in networks underlying communication and social cognition. The uncinate and arcuate fasciculi are integral to these networks, thus studying potential abnormalities in these white matter connections can further our understanding of anger and aggression problems in military veterans. Here, we use diffusion tensor imaging tractography to investigate white matter microstructural properties of the uncinate fasciculus and the arcuate fasciculus in veterans with and without anger and aggression problems. A control tract, the parahippocampal cingulum was also included in the analyses. More specifically, fractional anisotropy (FA) estimates are derived along the trajectory from all fiber pathways and compared between both groups. No between-group FA differences are observed for the uncinate fasciculus and the cingulum, however parts of the arcuate fasciculus show a significantly lower FA in the group of veterans with aggression and anger problems. Our data suggest that abnormalities in arcuate fasciculus white matter connectivity that are related to self-regulation may play an important role in the etiology of anger and aggression in military veterans.

The basolateral amygdala regulation of complex cognitive behaviours in the five-choice serial reaction time task

RATIONALE

The basolateral amygdala (BLA) plays important roles in the cognitive control in human and non-human animals. However, inconsistent findings between species have been observed and there have been relatively few detailed investigations of the cognitive properties of BLA, especially in mice.

OBJECTIVE

Our aim was to determine the role of BLA in cognition by using optogenetic manipulations.

METHODS

Male C57BL/six mice were trained and tested on the five-choice serial reaction time task (5-CSRTT), open-field test (OFT), elevated plus maze (EPM), Y-maze, and novel object recognition (NOR) test during optogenetic stimulation and inhibition of the BLA.

RESULTS

Optogenetic activation of the BLA decreased the impulsivity and increased the compulsivity of mice, whereas optogenetic inhibition of BLA had the opposite effect. Similarly, anxiety-like behaviours and spatial working memory were increased in BLA activation mice, whereas BLA inhibition decreased these behaviours. However, both BLA activation and inhibition decreased the motivation of the mice.

CONCLUSIONS

These data demonstrate that the BLA regulates impulsive action and spatial working memory, and plays a critical role in anxiety-like behaviours.

The Predictive Value of Early-Life Trauma, Psychopathy, and the Testosterone-Cortisol Ratio for Impulsive Aggression Problems in Veterans

Background

In this study, we examined whether early-life trauma, psychopathy, and the testosterone/cortisol ratio predicted impulsive aggression problems in veterans.

Method

A sample of 49 male veterans with impulsive aggression problems and 51 nonaggressive veterans were included in the study. Logistic regression analysis was performed with early-life trauma, primary and secondary psychopathy, and testosterone/cortisol ratio as continuous predictor variables; impulsive aggression status was entered as a binary outcome measure. Correlation analyses were conducted to examine pairwise relations among the predictors.

Results

Results indicated that early-life trauma and secondary psychopathy, but not the testosterone/cortisol ratio or primary psychopathy, were significant predictors of impulsive aggression status.

Conclusions

The current results indicate that early-life trauma and secondary psychopathy are risk factors for impulsive aggression problems among veterans. Future studies are needed to determine the exact causal relations among the variables examined here.

Genetic contribution to the phenotypic correlation between trait impulsivity and resting-state functional connectivity of the amygdala and its subregions

Trait impulsivity, a predisposition to respond to stimuli without regard for the potentially negative consequences, contributes to many maladaptive behaviors. Studies have shown that both genetic factors and interregional functional interactions underlie trait impulsivity. However, whether common genes contribute to both trait impulsivity and its neural basis is still unknown. This study investigated the phenotypic correlations between trait impulsivity and the resting-state functional connectivity (rsFC) of the amygdala as well as its subregions and the genetic contribution to the phenotypic correlations. By recruiting a sample of 292 twins in late adolescence and young adulthood, we found that trait impulsivity was positively correlated with the rsFC between the left full amygdala and the right dorsolateral prefrontal cortex (DLPFC). Further analyses on the subregions of the amygdala showed that trait impulsivity was positively correlated with the rsFCs between the left basolateral (BL) amygdala and both the right DLPFC and the right inferior frontal gyrus and with the rsFCs between the right superficial (SF) amygdala and both the dorsal anterior cingulate cortex and right anterior insula. Bivariate genetic modelling analyses found genetic overlaps between trait impulsivity and the rsFC of the left full amygdala or the left BL amygdala with the right DLPFC. The proportions of phenotypic associations accounted for by overlapping genes were 82% and 60%, respectively. These results provide evidence for the genetic overlap between trait impulsivity and the intrinsic brain functional connectivity centered at the amygdala and especially at its BL subregion.

Amygdala and Hypothalamus: Historical Overview With Focus on Aggression

Aggressiveness has a high prevalence in psychiatric patients and is a major health problem. Two brain areas involved in the neural network of aggressive behavior are the amygdala and the hypothalamus. While pharmacological treatments are effective in most patients, some do not properly respond to conventional therapies and are considered medically refractory. In this population, surgical procedures (ie, stereotactic lesions and deep brain stimulation) have been performed in an attempt to improve symptomatology and quality of life. Clinical results obtained after surgery are difficult to interpret, and the mechanisms responsible for postoperative reductions in aggressive behavior are unknown. We review the rationale and neurobiological characteristics that may help to explain why functional neurosurgery has been proposed to control aggressive behavior.

The Brain Resting-State Functional Connectivity Underlying Violence Proneness: Is It a Reliable Marker for Neurocriminology? A Systematic Review

Introduction: There is growing scientific interest in understanding the biological mechanisms affecting and/or underlying violent behaviors in order to develop effective treatment and prevention programs. In recent years, neuroscientific research has tried to demonstrate whether the intrinsic activity within the brain at rest in the absence of any external stimulation (resting-state functional connectivity; RSFC) could be employed as a reliable marker for several cognitive abilities and personality traits that are important in behavior regulation, particularly, proneness to violence. Aims: This review aims to highlight the association between the RSFC among specific brain structures and the predisposition to experiencing anger and/or responding to stressful and distressing situations with anger in several populations. Methods: The scientific literature was reviewed following the PRISMA quality criteria for reviews, using the following digital databases: PubMed, PsycINFO, Psicodoc, and Dialnet. Results: The identification of 181 abstracts and retrieval of 34 full texts led to the inclusion of 17 papers. The results described in our study offer a better understanding of the brain networks that might explain the tendency to experience anger. The majority of the studies highlighted that diminished RSFC between the prefrontal cortex and the amygdala might make people prone to reactive violence, but that it is also necessary to contemplate additional cortical (i.e., insula, gyrus [angular, supramarginal, temporal, fusiform, superior, and middle frontal], anterior and posterior cingulated cortex) and subcortical brain structures (i.e., hippocampus, cerebellum, ventral striatum, and nucleus centralis superior) in order to explain a phenomenon as complex as violence. Moreover, we also described the neural pathways that might underlie proactive violence and feelings of revenge, highlighting the RSFC between the OFC, ventral striatal, angular gyrus, mid-occipital cortex, and cerebellum. Conclusions. The results from this synthesis and critical analysis of RSFC findings in several populations offer guidelines for future research and for developing a more accurate model of proneness to violence, in order to create effective treatment and prevention programs.

Altered Amygdala Excitation and CB1 Receptor Modulation of Aggressive Behavior in the Neuroligin-3R451C Mouse Model of Autism

Understanding neuronal mechanisms underlying aggression in patients with autism spectrum disorder (ASD) could lead to better treatments and prognosis. The Neuroligin-3 (NL3)^R451C mouse model of ASD has a heightened aggressive phenotype, however the biological mechanisms underlying this behavior are unknown. It is well established that NL3^R451C mice have imbalanced excitatory and inhibitory synaptic activity in the hippocampus and somatosensory cortex. The amygdala plays a role in modulating aggressive behavior, however potential changes in synaptic activity in this region have not previously been assessed in this model. We investigated whether aggressive behavior is robustly present in mice expressing the R451C mutation, following back-crossing onto a congenic background strain. Endocannabinoids influence social interaction and aggressive behavior, therefore we also studied the effects of cannabinoid receptor 1 (CB1) agonist on NL3^R451C mice. We report that NL3^R451C mice have increased amplitude of miniature excitatory postsynaptic currents (EPSCs) with a concomitant decrease in the amplitude of inhibitory postsynaptic currents (IPSCs) in the basolateral amygdala. Importantly, we demonstrated that NL3^R451C mice bred on a C57Bl/6 background strain exhibit an aggressive phenotype. Following non-sedating doses (0.3 and 1.0 mg/kg) of the CB1 receptor agonist WIN55,212-2 (WIN), we observed a significant reduction in aggressive behavior in NL3^R451C mice. These findings demonstrate altered synaptic activity in the basolateral amygdala and suggest that the NL3^R451C mouse model is a useful preclinical tool to understand the role of CB1 receptor function in aggressive behavior.