Identification of central amygdala and trigeminal motor nucleus connectivity in humans: An ultra-high field diffusion MRI study.

The neuroanatomical circuitry of jaw muscles has been mostly explored in non-human animals. A recent rodent study revealed a novel circuit from the central amygdala (CeA) to the trigeminal motor nucleus (5M), which controls biting attacks. This circuit has yet to be delineated in humans. Ultra-high diffusion-weighted imaging data from the Human Connectome Project (HCP) allow in vivo delineation of circuits identified in other species-for example, the CeA-5M pathway-in humans. We hypothesized that the CeA-5M circuit could be resolved in humans at both 7 and 3 T. We performed probabilistic tractography between the CeA and 5M in 30 healthy young adults from the HCP database. As a negative control, we performed tractography between the basolateral amygdala (BLAT) and 5M, as CeA is the only amygdalar nucleus with extensive projections to the brainstem. Connectivity strength was operationalized as the number of streamlines between each region of interest. Connectivity strength between CeA-5M and BLAT-5M within each hemisphere was compared, and CeA-5M circuit had significantly stronger connectivity than the BLAT-5M circuit, bilaterally at both 7 T (all p < .001) and 3 T (all p < .001). This study is the first to delineate the CeA-5M circuit in humans.

Dynamic integration and segregation of amygdala subregional functional circuits linking to physiological arousal.

The dynamical organization of brain networks is essential to support human cognition and emotion for rapid adaption to ever-changing environment. As the core nodes of emotion-related brain circuitry, the basolateral amygdala (BLA) and centromedial amygdala (CMA) as two major amygdalar nuclei, are recognized to play distinct roles in affective functions and internal states, via their unique connections with cortical and subcortical structures in rodents. However, little is known how the dynamical organization of emotion-related brain circuitry reflects internal autonomic responses in humans. Using resting-state functional magnetic resonance imaging (fMRI) with K-means clustering approach in a total of 79 young healthy individuals (cohort 1: 42; cohort 2: 37), we identified two distinct states of BLA- and CMA-based intrinsic connectivity patterns, with one state (integration) showing generally stronger BLA- and CMA-based intrinsic connectivity with multiple brain networks, while the other (segregation) exhibiting weaker yet dissociable connectivity patterns. In an independent cohort 2 of fMRI data with concurrent recording of skin conductance, we replicated two similar dynamic states and further found higher skin conductance level in the integration than segregation state. Moreover, machine learning-based Elastic-net regression analyses revealed that time-varying BLA and CMA intrinsic connectivity with distinct network configurations yield higher predictive values for spontaneous fluctuations of skin conductance level in the integration than segregation state. Our findings highlight dynamic functional organization of emotion-related amygdala nuclei circuits and networks and its links to spontaneous autonomic arousal in humans.

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.

The effects of morphine withdrawal and conditioned withdrawal on memory consolidation and c-Fos expression in the central amygdala.

The current study tested the hypothesis that drug withdrawal contributes to the addiction cycle in part because of an action on memory consolidation. Hence, four experiments in male Sprague-Dawley rats compared the effects of precipitated morphine withdrawal and conditioned morphine withdrawal on the consolidation of object memory and on activation of c-Fos in the central nucleus of the amygdala (CeA). It was found that immediate, but not 6 h delayed, post sample administration of 3 mg/kg of naltrexone significantly enhanced object memory in rats maintained, or previously maintained, on 10 mg/kg/day of morphine via osmotic minipumps. To establish whether conditioned withdrawal could also alter object memory, a contextual conditioning procedure was employed whereby morphine-maintained (10 mg/kg/day) animals received naltrexone (3 mg/kg) in a distinctive context (CS+) and vehicle in a separate context (CS-) for 10 days. During conditioning in the CS+, naltrexone suppressed locomotor activity, caused a rapid body weight loss and increased frequency of wet dog shakes. Interestingly, confinement to this CS+ immediately, but not 6 h, after the sample phase, also enhanced object memory. Finally, posttraining naltrexone and exposure to the CS+ both induced significant expression of c-Fos in the CeA. Therefore, this study reports for the first time that both acute precipitated withdrawal and conditioned withdrawal can facilitate memory consolidation, possibly through a common neural pathway that involves the central amygdala.

An Amygdala Circuit Mediates Experience-Dependent Momentary Arrests during Exploration.

Exploration of novel environments ensures survival and evolutionary fitness. It is expressed through exploratory bouts and arrests that change dynamically based on experience. Neural circuits mediating exploratory behavior should therefore integrate experience and use it to select the proper behavioral output. Using a spatial exploration assay, we uncovered an experience-dependent increase in momentary arrests in locations where animals arrested previously. Calcium imaging in freely exploring mice revealed a genetically and projection-defined neuronal ensemble in the basolateral amygdala that is active during self-paced behavioral arrests. This ensemble was recruited in an experience-dependent manner, and closed-loop optogenetic manipulation of these neurons revealed that they are sufficient and necessary to drive experience-dependent arrests during exploration. Projection-specific imaging and optogenetic experiments revealed that these arrests are effected by basolateral amygdala neurons projecting to the central amygdala, uncovering an amygdala circuit that mediates momentary arrests in familiar places but not avoidance or anxiety/fear-like behaviors.

Anatomic alterations across amygdala subnuclei in medication-free patients with obsessive-compulsive disorder.

Background: The amygdala has been implicated in obsessive-compulsive disorder (OCD), a common, disabling illness. However, the regional distribution of anatomic alterations in this structure and their association with the symptoms of OCD remains to be established. Methods: We collected high-resolution 3D T1-weighted images from 81 untreated patients with OCD and no lifetime history of comorbid psychotic, affective or anxiety disorders, and from 95 age- and sex-matched healthy controls. We extracted the volume of the central nucleus of the amygdala (CeA) and the basolateral complex of the amygdala (BLA) and compared them across groups using FreeSurfer 6.0. In exploratory analyses, we evaluated other subnuclei, including the cortical medial nuclei, the anterior amygdaloid area, and the corticoamygdaloid transition area. Results: Patients with OCD had reduced amygdala volume bilaterally compared with healthy controls (left, p = 0.034; right, p = 0.002). Volume reductions were greater in the CeA (left: -11.9%, p = 0.002; right: -13.3%, p < 0.001) than in the BLA (left lateral nucleus: -3.3%, p = 0.029; right lateral nucleus: -3.9%, p = 0.018; right basal nucleus: -4.1%, p = 0.017; left accessory basal nucleus: -6.5%, p = 0.001; right accessory basal nucleus: -9.3%, p < 0.001). Volume reductions in the CeA were associated with illness duration. Exploratory analysis revealed smaller medial (left: -15.4%, p < 0.001, η2 = 0.101) and cortical (left: -9.1%, p = 0.001, η2 = 0.058; right: -15.4%, p < 0.001, η2 = 0.175) nuclei in patients with OCD compared with healthy controls. Limitations: Although the strict exclusion criteria used in the study helped us to identify OCD-specific alterations, they may have limited generalizability to the broader OCD population. Conclusion: Our results provide a comprehensive anatomic profile of alterations in the amygdala subnuclei in untreated patients with OCD and highlight a distinctive pattern of volume reductions across subnuclei in OCD. Based on the functional properties of the amygdala subnuclei established from preclinical research, CeA impairment may contribute to behavioural inflexibility, and BLA disruption may be responsible for altered fear conditioning and the affective components of OCD.

Selective modulation of tonic aversive qualities of neuropathic pain by morphine in the central nucleus of the amygdala requires endogenous opioid signaling in the anterior cingulate cortex.

The amygdala is a key subcortical region believed to contribute to emotional components of pain. As opioid receptors are found in both the central (CeA) and basolateral (BLA) nuclei of the amygdala, we investigated the effects of morphine microinjection on evoked pain responses, pain-motivated behaviors, dopamine release in the nucleus accumbens (NAc), and descending modulation in rats with left-side spinal nerve ligation (SNL). Morphine administered into the right or left CeA had no effect on nerve injury-induced tactile allodynia or mechanical hyperalgesia. Right, but not left, CeA morphine produced conditioned place preference (CPP) and increased extracellular dopamine in the NAc selectively in SNL rats, suggesting relief of aversive qualities of ongoing pain. In SNL rats, CPP and NAc dopamine release following right CeA morphine was abolished by blocking mu opioid receptor signaling in the rostral anterior cingulate cortex (rACC). Right CeA morphine also significantly restored SNL-induced loss of the diffuse noxious inhibitory controls, a spino-bulbo-spinal pain modulatory mechanism, termed conditioned pain modulation in humans. Microinjection of morphine into the BLA had no effects on evoked behaviors and did not produce CPP in nerve-injured rats. These findings demonstrate that the amygdalar action of morphine is specific to the right CeA contralateral to the side of injury and results in enhancement of net descending inhibition. In addition, engagement of mu opioid receptors in the right CeA modulates affective qualities of ongoing pain through endogenous opioid neurotransmission within the rACC, revealing opioid-dependent functional connections from the CeA to the rACC.

Resting-state connectivity of the bed nucleus of the stria terminalis and the central nucleus of the amygdala in clinical anxiety

Background: The central nucleus of the amygdala and bed nucleus of the stria terminalis are involved primarily in phasic and sustained aversive states. Although both structures have been implicated in pathological anxiety, few studies with a clinical population have specifically focused on them, partly because of their small size. Previous work in our group used high-resolution imaging to map the restingstate functional connectivity of the bed nucleus of the stria terminalis and the central nucleus of the amygdala in healthy subjects at 7 T, confirming and extending structural findings in humans and animals, while providing additional insight into cortical connectivity that is potentially unique to humans. Methods: In the current follow-up study, we contrasted resting-state functional connectivity in the bed nucleus of the stria terminalis and central nucleus of the amygdala at 7 T between healthy volunteers (n = 30) and patients with generalized and/or social anxiety disorder (n = 30). Results: Results revealed significant voxel-level group differences. Compared with healthy volunteers, patients showed stronger resting-state functional connectivity between the central nucleus of the amygdala and the lateral orbitofrontal cortex and superior temporal sulcus. They also showed weaker resting-state functional connectivity between the bed nucleus of the stria terminalis and the dorsolateral prefrontal cortex and occipital cortex. Limitations: These findings depart from a previous report of resting-state functional connectivity in the central nucleus of the amygdala and bed nucleus of the stria terminalis under sustained threat of shock in healthy volunteers. Conclusion: This study provides functional MRI proxies of the functional dissociation of the bed nucleus of the stria terminalis and central nucleus of the amygdala, and suggests that resting-state functional connectivity of key structures in the processing of defensive responses do not recapitulate changes related to induced state anxiety. Future work needs to replicate and further probe the clinical significance of these findings.

Resting-State Functional Connectivity Between Centromedial Amygdala and Insula as Related to Somatic Symptoms in Depressed Patients: A Preliminary Study.

OBJECTIVE: Somatic symptoms are prevalent in patients with depression. The centromedial amygdala (CMA) is a key brain region that mediates autonomic and somatic responses. Abnormal function in the CMA may contribute to the development of somatic symptoms in depressed patients. METHODS: We compared the resting-state functional connectivity (RSFC) based on the seed of the left and right CMA between 37 patients with depression and 30 healthy controls. The severity of depressive and somatic symptoms was assessed using the Hamilton Depression Rating Scale (HDRS) and the 15-item somatic symptom severity scale of the Patient Health Questionnaire (PHQ-15). Correlation analysis was performed to investigate the relationship between the RSFC and clinical variables (HDRS and PHQ-15) in depressed patients. RESULTS: Compared with healthy controls, patients with depression exhibited decreased RSFC between the CMA and insula, and superior temporal gyrus. In addition, functional connectivity between the left CMA and left insula was negatively correlated with PHQ-15 (r = -0.348, p = .037) in depressed patients. No significant relation was found between the RSFC and HDRS in depressed patients. CONCLUSIONS: Functional connectivity between the CMA and insula is reduced in depressive patients, which is associated with the severity of somatic symptoms. Our findings may provide a potential neural substrate to interpret the co-occurrence of depression with somatic symptoms.

Tratamiento de la agresividad refractaria mediante amigdalotomía e hipotalamotomía posteromedial por radiofrecuencia / Treatment of refractory aggressiveness by amygdalotomy and posteromedial hypothalamotomy by radiofrequency

Introducción. Dado que, en algunas circunstancias, las conductas defensivas o de ataque muestran un patrón de dominancia motora, tal como se observa en los sujetos dedicados a los deportes de contacto o de lucha, se consideró que la conducta agresiva tiene un patrón motor dominante. Con el fin de evitar los problemas funcionales descritos con los procedimientos de lesión bilateral tanto del núcleo central de la amígdala como del hipotálamo posteromedial, se decidió combinarlos; es decir, realizar amigdalotomía del núcleo central de la amígdala e hipotalamotomía posteromedial de manera unilateral y simultánea, basándose en la dominancia motora del paciente mediante la prueba de Edimburgo. Pacientes y métodos. Este estudio muestra la experiencia quirúrgica en una serie de nueve pacientes con el diagnóstico de síndrome neuroagresivo resistente al tratamiento farmacológico. Dentro del protocolo de estudio, se les realizó resonancia magnética cerebral para descartar la presencia de neoplasias, enfermedades vasculares, infecciones y trastornos degenerativos. El grado de agresividad se cuantificó mediante la escala global de agresividad de Yudofsky. Adicionalmente, se determinó la dominancia manual a través de la prueba de Edimburgo. Resultados y conclusiones. El buen control de la agresividad se observó de modo inmediato. En algunos casos fue necesario reducir la medicación de antipsicóticos o benzodiacepinas, ya que aumentaban la agresividad. Sólo un caso requirió una segunda cirugía. Se logró seguimiento del 100% de los casos en 24 meses y del 78% en 36 meses

Introduction. Since, under certain circumstances, defensive or attacking behaviours display a pattern of motor dominance, as observed in subjects who participate in contact or fighting sports, aggressive behaviour was considered to have a dominant motor pattern. With the aim of preventing the functional problems reported with bilateral lesion procedures involving both the central nucleus of the amygdala and the posteromedial hypothalamus, the decision was made to combine them; thus, an amygdalotomy of the central nucleus of the amygdala and a posteromedial hypothalamotomy were to be performed simultaneously and unilaterally, on the basis of the motor dominance of the patient determined by means of the Edinburgh test. Patients and methods. This study describes the surgical experience in a series of nine patients diagnosed with refractory neuroaggressive syndrome. As part of the study protocol, a magnetic resonance brain scan was performed to rule out the presence of neoplasms, vascular diseases, infections and degenerative disorders. The degree of aggressiveness was quantified using Yudofsky's Overt Aggression Scale. Additionally, manual dominance was determined by means of the Edinburgh test. Results and conclusions. Good control of aggressiveness was seen immediately. In some cases it was necessary to reduce the antipsychotic or benzodiazepine medication, as it was seen to increase aggressiveness. Only one case required a second surgical intervention. Follow-up was achieved in 100% of the cases at 24 months and 78% at 36 months

The central extended amygdala in fear and anxiety: Closing the gap between mechanistic and neuroimaging research.

Anxiety disorders impose a staggering burden on public health, underscoring the need to develop a deeper understanding of the distributed neural circuits underlying extreme fear and anxiety. Recent work highlights the importance of the central extended amygdala, including the central nucleus of the amygdala (Ce) and neighboring bed nucleus of the stria terminalis (BST). Anatomical data indicate that the Ce and BST form a tightly interconnected unit, where different kinds of threat-relevant information can be integrated to assemble states of fear and anxiety. Neuroimaging studies show that the Ce and BST are engaged by a broad spectrum of potentially threat-relevant cues. Mechanistic work demonstrates that the Ce and BST are critically involved in organizing defensive responses to a wide range of threats. Studies in rodents have begun to reveal the specific molecules, cells, and microcircuits within the central extended amygdala that underlie signs of fear and anxiety, but the relevance of these tantalizing discoveries to human experience and disease remains unclear. Using a combination of focal perturbations and whole-brain imaging, a new generation of nonhuman primate studies is beginning to close this gap. This work opens the door to discovering the mechanisms underlying neuroimaging measures linked to pathological fear and anxiety, to understanding how the Ce and BST interact with one another and with distal brain regions to govern defensive responses to threat, and to developing improved intervention strategies.

Acute alcohol administration dampens central extended amygdala reactivity.

Alcohol use is common, imposes a staggering burden on public health, and often resists treatment. The central extended amygdala (EAc)-including the bed nucleus of the stria terminalis (BST) and the central nucleus of the amygdala (Ce)-plays a key role in prominent neuroscientific models of alcohol drinking, but the relevance of these regions to acute alcohol consumption in humans remains poorly understood. Using a single-blind, randomized-groups design, multiband fMRI data were acquired from 49 social drinkers while they performed a well-established emotional faces paradigm after consuming either alcohol or placebo. Relative to placebo, alcohol significantly dampened reactivity to emotional faces in the BST. To rigorously assess potential regional differences in activation, data were extracted from unbiased, anatomically predefined regions of interest. Analyses revealed similar levels of dampening in the BST and Ce. In short, alcohol transiently reduces reactivity to emotional faces and it does so similarly across the two major divisions of the human EAc. These observations reinforce the translational relevance of addiction models derived from preclinical work in rodents and provide new insights into the neural systems most relevant to the consumption of alcohol and to the initial development of alcohol abuse in humans.

Extended amygdala connectivity changes during sustained shock anticipation.

The bed nucleus of the stria terminalis (BNST) and central amygdala (CeA) of the extended amygdala are small, anatomically interconnected brain regions. They are thought to mediate responses to sustained, unpredictable threat stimuli and phasic, predictable threat stimuli, respectively. They perform these operations largely through their interconnected networks. In two previous studies, we mapped and contrasted the resting functional connectivity networks of the BNST and CeA at 7 Tesla with high resolution. This follow-up study investigates the changes in functional connectivity of these structures during sustained anticipation of electric shock. Results show that the BNST and CeA become less strongly coupled with the ventromedial prefrontal cortex (vmPFC), cingulate, and nucleus accumbens in shock threat relative to a safety condition. In addition, the CeA becomes more strongly coupled with the thalamus under threat. An exploratory, whole-brain connectivity analysis reveals that, although the BNST/CeA exhibits generally decreased connectivity, many other cortical regions demonstrate greater coupling under threat than safety. Understanding the differential network structures of these two regions and how they contribute to processing under threat will help elucidate the building blocks of the anxious state.

Intrinsic functional connectivity of the central nucleus of the amygdala and bed nucleus of the stria terminalis.

The central nucleus of the amygdala (CeA) and bed nucleus of the stria terminalis (BNST), two nuclei within the central extended amygdala, function as critical relays within the distributed neural networks that coordinate sensory, emotional, and cognitive responses to threat. These structures have overlapping anatomical projections to downstream targets that initiate defensive responses. Despite these commonalities, researchers have also proposed a functional dissociation between the CeA and BNST, with the CeA promoting responses to discrete stimuli and the BNST promoting responses to diffuse threat. Intrinsic functional connectivity (iFC) provides a means to investigate the functional architecture of the brain, unbiased by task demands. Using ultra-high field neuroimaging (7-Tesla fMRI), which provides increased spatial resolution, this study compared the iFC networks of the CeA and BNST in 27 healthy individuals. Both structures were coupled with areas of the medial prefrontal cortex, hippocampus, thalamus, and periaqueductal gray matter. Compared to the BNST, the bilateral CeA was more strongly coupled with the insula and regions that support sensory processing, including thalamus and fusiform gyrus. In contrast, the bilateral BNST was more strongly coupled with regions involved in cognitive and motivational processes, including the dorsal paracingulate gyrus, posterior cingulate cortex, and striatum. Collectively, these findings suggest that responses to sensory stimulation are preferentially coordinated by the CeA and cognitive and motivational responses are preferentially coordinated by the BNST.

Bidirectional Control of Social Behavior by Activity within Basolateral and Central Amygdala of Primates.

UNLABELLED: Both hypoactivity and hyperactivity in the amygdala are associated with perturbations in social behavior. While >60 years of experimental manipulations of the amygdala in animal models have shown that amygdala is critical for social behavior, many of these studies contradict one another. Moreover, several questions remain unaddressed. (1) What effect does activation of amygdala have on social behavior? (2) What is the effect of transient silencing, rather than permanent damage? (3) Is there a dissociation between the roles of the central (CeA) and basolateral amygdala (BLA) in regulating social behavior? (4) Can the prosocial effects of amygdala manipulations be explained by anxiolytic effects? We focally manipulated activity within the CeA or BLA in macaques by intracerebral microinjection of muscimol (to inactivate) or bicuculline (to activate) to these amygdaloid subregions. Social interactions were observed in pairs of highly familiar monkeys. We compared these effects to those achieved with systemic diazepam. Activation of the BLA but not CeA suppressed social behavior. Inhibition of either structure increased social behavior, although the effect was greater following inhibition of the BLA. Systemic diazepam was without effect. These studies, which are the first to bidirectionally manipulate the primate amygdala for effects on social behavior, revealed that (1) the amygdala, as a critical regulator of the social network, is bidirectionally sensitive to perturbations in activity, and (2) increased sociability after amygdala inactivation cannot be solely explained by decreased fear. SIGNIFICANCE STATEMENT: Many previous studies reported loss of social interactions following permanent damage to the amygdala in nonhuman primates. In contrast, we report that transient inhibition of the basolateral amygdala triggered a profound increase in social interactions in dyads of monkeys highly familiar with each other. We compared these effects to those of systemic diazepam, which failed to increase social behavior. While it has been suggested that suppression of "fear" could underlie the prosocial effects of amygdala manipulations, our data strongly suggest that impairment in fear processing per se cannot account for the prosocial effects of amygdala inhibition. Furthermore, our studies are the first to examine activation of the amygdala and to assess the separate roles of the amygdaloid nuclei in social behavior in primates.

Overexpressing Corticotropin-Releasing Factor in the Primate Amygdala Increases Anxious Temperament and Alters Its Neural Circuit.

BACKGROUND: Nonhuman primate models are critical for understanding mechanisms underlying human psychopathology. We established a nonhuman primate model of anxious temperament (AT) for studying the early-life risk to develop anxiety and depression. Studies have identified the central nucleus of the amygdala (Ce) as an essential component of AT's neural substrates. Corticotropin-releasing factor (CRF) is expressed in the Ce, has a role in stress, and is linked to psychopathology. Here, in young rhesus monkeys, we combined viral vector technology with assessments of anxiety and multimodal neuroimaging to understand the consequences of chronically increased CRF in the Ce region. METHODS: Using real-time intraoperative magnetic resonance imaging-guided convection-enhanced delivery, five monkeys received bilateral dorsal amygdala Ce-region infusions of adeno-associated virus serotype 2 containing the CRF construct. Their cagemates served as unoperated control subjects. AT, regional brain metabolism, resting functional magnetic resonance imaging, and diffusion tensor imaging were assessed before and 2 months after viral infusions. RESULTS: Dorsal amygdala CRF overexpression significantly increased AT and metabolism within the dorsal amygdala. Additionally, we observed changes in metabolism in other AT-related regions, as well as in measures of functional and structural connectivity. CONCLUSIONS: This study provides a translational roadmap that is important for understanding human psychopathology by combining molecular manipulations used in rodents with behavioral phenotyping and multimodal neuroimaging measures used in humans. The results indicate that chronic CRF overexpression in primates not only increases AT but also affects metabolism and connectivity within components of AT's neural circuitry.