Organization of Valence-Encoding and Projection-Defined Neurons in the Basolateral Amygdala

A reduced ability to discriminate social from non-social touch at the circuit level may underlie social avoidance in autism

Social touch is critical for communication to impart emotions and intentions. However, certain autistic individuals experience aversion to social touch. Here, we used Neuropixels probes to record neural responses to social vs. non-social interactions in somatosensory cortex, tail of striatum, and basolateral amygdala. We find that wild type mice show aversion to repeated presentations of an inanimate object but not of another mouse. Cortical neurons are modulated especially by touch context (social vs. object), while striatal neurons change their preference depending on whether mice could choose or not to interact. In contrast, Fmr1 knockout (KO) mice, a model of autism, find social and non-social interactions equally aversive, especially at close proximity, and their cortical/striatal neurons are less able to discriminate social valence. A linear model shows that the encoding of certain avoidance/aversive behaviors in cortical neuron activity differed between genotypes. Thus, a reduced capacity to represent social stimuli at the circuit level may underlie social avoidance in autism.

From valence encoding to motivated behavior: A focus on the nucleus accumbens circuitry

How do our brains determine whether something is good or bad? The brain's ability to evaluate stimuli as positive or negative - by attributing valence - is fundamental to survival and decision-making. Different brain regions have been associated with valence encoding, including the nucleus accumbens (NAc). The NAc is predominantly composed of GABAergic medium spiny neurons (MSNs), which segregate into two distinct populations based on their dopamine receptor expression: D1-receptor-expressing (D1-MSNs) and D2-receptor-expressing neurons (D2-MSNs). Classical models propose a binary functional role, where D1-MSNs exclusively mediated reward and positive valence, while D2-MSNs processed aversion and negative valence. However, we now recognize that NAc MSN subpopulations operate in a more complex manner than previously thought, often working cooperatively rather than antagonistically in valence-related behaviors. This review synthesizes our current knowledge of valence-encoding neurocircuitry, with emphasis on the NAc. We examine electrophysiological, calcium imaging, optogenetic, chemogenetic and pharmacological studies detailing the contribution of NAc medium spiny neurons for rewarding and aversive responses. Finally, we explore emerging technical innovations that promise to advance our understanding of how the mammalian brain encodes valence and translates it into behavior.

Estradiol, via estrogen receptor β signaling, mediates stress-susceptibility in the male brain

Dysregulation of normal reward processing via psychological stress contributes to the development of psychiatric disorders. Estrogen is involved in reward processing in females, but this effect has not been well studied in males despite the abundant conversion of androgens to estrogens in the male brain. Here, we used a combination of genetic deletions, behavioral assays, pharmacology, circuit dissection, electrophysiology, in vivo fiber photometry, and optogenetics/chemogenetics to determine the role of the most prevalent and potent estrogen, 17β-estradiol, in male stress-induced reward processing dysfunction. We found that absence of estrogen receptor (ER) β renders male but not female mice susceptible to stress-induced maladaptive reward-processing behaviors. We demonstrated that activation of ERβ-projecting neurons from the basolateral amygdala to nucleus accumbens induced rewarding effects in male, but not female mice. Moreover, we show that the activity of ERβ-expressing neurons projecting from the basolateral amygdala to nucleus accumbens is reduced in hypogonadal male mice subjected to stress, while activation of this circuit reverses stress-induced maladaptive reward processing behaviors and inhibition induces stress susceptibility. We identified that absence of estradiol, but not testosterone per se, underlies susceptibility to stress-mediated dysfunction of rewarding behaviors and that brain-selective delivery of estradiol and intra-basolateral amygdala administration of an ERβ-specific agonist prevent maladaptive reward-processing behaviors in hypogonadal male mice. These findings delineate an estrogen-based mechanism underlying stress susceptibility and provide a novel therapeutic strategy for the treatment of reward-related disorders associated with hypogonadal conditions.

Biased Information Routing Through the Basolateral Amygdala, Altered Valence Processing, and Impaired Affective States Associated With Psychiatric Illnesses

Accumulating evidence supports a role for altered circuit function in impaired valence processing and altered affective states as a core feature of psychiatric illnesses. We review the circuit mechanisms underlying normal valence processing and highlight evidence supporting altered function of the basolateral amygdala, valence processing, and affective states across psychiatric illnesses. The mechanisms controlling network activity that governs valence processing are reviewed in the context of potential pathophysiological mechanisms mediating circuit dysfunction and impaired valence processing in psychiatric illnesses. Finally, we review emerging data demonstrating experience-dependent, biased information routing through the basolateral amygdala promoting negative valence processing and discuss the potential relevance to impaired affective states and psychiatric illnesses.

Social stress increases anxiety by GluA1-dependent synaptic strengthening of ventral tegmental area inputs to the basolateral amygdala

BACKGROUND

Brain defensive mechanisms evolved to maintain low levels of state anxiety. However, risk factors such as stress exposure shifts activity within defensive circuits, resulting in increased anxiety. The amygdala is a crucial node for maintaining adaptive anxiety levels, and amygdala hyperactivity can lead to pathological anxiety through mechanisms that are not well understood.

METHODS

We used chronic social defeat stress (CSD) in mice. We combined anatomical tracing methods, patch-clamp recordings and optogenetics to probe how synaptic inputs from the ventral tegmental area (VTA) to the basolateral amygdala (BLA) are affected by CSD. We performed in vivo fiber photometry recordings to track inputs onto basolateral amygdala. Array tomography and electron microscopy were used to unravel the structural composition of VTA-BLA synapses.

RESULTS

We identified the VTA as a source of glutamatergic inputs to the BLA potentiated by stress. In turn, inputs from mPFC were not potentiated. BLA-projecting VTA glutamatergic neurons are activated by social stress, increasing their excitability and synaptic strength. In vivo potentiation of VTA glutamatergic inputs in the BLA is sufficient to increase anxiety. We showed that stress-induced synaptic strengthening is mediated by insertion of GluA1-containing AMPA receptors. Impeding GluA1 subunit trafficking in BLA neurons with VTA upstream inputs prevents stress-induced increase in synaptic firing and anxiety.

CONCLUSIONS

Potentiation of VTA inputs increases synaptic integration, enhancing amygdala activity and promoting maladaptive anxiety. Understanding the impact of amygdala hyperactivity could lead to targeted therapies, restoring circuit balance and offering new precision medicine approaches for anxiety disorders.

Amygdalo-cortical dialogue underlies memory enhancement by emotional association

Emotional arousal plays a critical role in determining what is remembered from experiences. It is hypothesized that activation of the amygdala by emotional stimuli enhances memory consolidation in its downstream brain regions. However, the physiological basis of the inter-regional interaction and its functions remain unclear. Here, by adding emotional information to a perceptual recognition task that relied on a frontal-sensory cortical circuit in mice, we demonstrated that the amygdala not only associates emotional information with perceptual information but also enhances perceptual memory retention via amygdalo-frontal cortical projections. Furthermore, emotional association increased reactivation of coordinated activity across the amygdalo-cortical circuit during non-rapid eye movement (NREM) sleep but not during rapid eye movement (REM) sleep. Notably, this increased reactivation was associated with amygdala high-frequency oscillations. Silencing of amygdalo-cortical inputs during NREM sleep selectively disrupted perceptual memory enhancement. Our findings indicate that inter-regional reactivation triggered by the amygdala during NREM sleep underlies emotion-induced perceptual memory enhancement.

Astrocyte ensembles manipulated with AstroLight tune cue-motivated behavior

Astrocytes, dynamic cells crucial to brain function, have traditionally been overshadowed by the emphasis on neuronal activity in regulating behavior. Unlike neurons, which are organized into ensembles that encode different brain representations, astrocytes have long been considered a homogeneous population. This is partly because of the lack of tools available to map and manipulate specific subsets of astrocytes based on their functional activity, obscuring the extent of their specialization in circuits. Here, using AstroLight, a tool that translates astrocytic activity-mediated calcium signals into gene expression in a light-dependent manner, we have identified an astrocytic ensemble, a functionally specified subset of astrocytes that emerges upon activity during cue-motivated behaviors in the nucleus accumbens, an integrator hub in the reward system. Furthermore, through gain-of-function and loss-of-function manipulations, we demonstrate that this ensemble is essential for modulating cue-reward associations. These findings highlight the specialization of astrocytes into ensembles and their fine-tuning role in shaping salient behavior.

Neural circuit plasticity transforms infant neglect into maternal care

Infants in distress evoke strong emotional responses in adults, which help to elicit caretaking behaviors from parents to ensure infant needs are met1-3. However, neonatal care can also be challenging, and interactions with infants can lead to stress and negative affect even in potential caregivers4-7. Child neglect and maltreatment rates in human populations make it important to understand the neural mechanisms of regulating negative emotions and stress in the parental brain8-10. Here we show how rapid plasticity in female mouse central amygdala (CeA) transforms infant aversion into attentiveness after initial pup experience. Projections from CeA to locus coeruleus (CeA→LC) were strongly activated upon initial pup contact leading to pup aversion. CeA→LC pup responses were reduced with parental experience and down-regulating CeA→LC activity led to less aversion. Oxytocin signaling in central amygdala was required to switch pup aversion to attention, inducing rapid long-term depression of excitatory inputs onto projection neurons. CeA→LC projectors released the stress hormone corticotropin-releasing factor onto LC neurons, modulating phasic firing to regulate attention. This circuit organization enables local CeA computations of pup valence to be broadcast throughout the brain by the LC central arousal system, leading to appropriate pup-directed behaviors depending on adult state.

An amygdala-cortical circuit for encoding generalized fear memories

Generalized learning is a fundamental process observed across species, contexts, and sensory modalities that enables animals to use past experiences to adapt to changing conditions. Evidence suggests that the prefrontal cortex (PFC) extracts general features of an experience that can be used across multiple situations. The anterior cingulate cortex (ACC), a region of the PFC, is implicated in generalized fear responses to novel contexts. However, the ACC's role in encoding contextual information is poorly understood, especially under increased threat intensity that promotes generalization. Here, we show that synaptic plasticity within the ACC and signaling from amygdala inputs during fear learning are necessary for generalized fear responses to novel encountered contexts. The ACC did not encode specific fear to the training context, suggesting this region extracts general features of a threatening experience rather than specific contextual information. Together with our previous work, our results demonstrate that generalized learning about threatening contexts is encoded, in part, within an ascending amygdala-cortical circuit, whereas descending ACC projections to the amygdala drive generalized fear responses during exposure to novel contexts. Our results further demonstrate that schematic learning can occur in the PFC after single-trial learning, a process typically attributed to learning over many repeated learning episodes.

Multisensory integration of social signals by a pathway from the basal amygdala to the auditory cortex in maternal mice

Social encounters are inherently multisensory events, yet how and where social cues of distinct sensory modalities merge and interact in the brain is poorly understood. When their pups wander away from the nest, mother mice use a combination of vocal and olfactory signals emitted by the pups to locate and retrieve them. Previous work revealed the emergence of multisensory interactions in the auditory cortex (AC) of both dams and virgins who cohabitate with pups ("surrogates"). Here, we identify a neural pathway that relays information about odors to the AC to be integrated with responses to sound. We found that a scattered population of glutamatergic neurons in the basal amygdala (BA) projects to the AC and responds to odors, including the smell of pups. These neurons exhibit increased activity when the female is searching for pups that terminates upon contact. Finally, we show that selective optogenetic activation of BA-AC neurons modulates responses to pup calls, and that this modulation switches from predominantly suppressive to predominantly excitatory after maternal experience. This supports an underappreciated role for the amygdala in directly shaping sensory representations in an experience-dependent manner. We propose that the BA-AC pathway supports integration of olfaction and audition to facilitate maternal care and speculate that it may carry valence information to the AC.

Identification of a stress-responsive subregion of the basolateral amygdala in male rats

The basolateral amygdala (BLA) is reliably activated by psychological stress and hyperactive in conditions of pathological stress or trauma; however, subsets of BLA neurons are also readily activated by rewarding stimuli and can suppress fear and avoidance behaviours. The BLA is highly heterogeneous anatomically, exhibiting continuous molecular and connectivity gradients throughout the entire structure. A critical gap remains in understanding the anatomical specificity of amygdala subregions, circuits, and cell types explicitly activated by acute stress and how they are dynamically activated throughout stimulus exposure. Using a combination of topographical mapping for the activity-responsive protein FOS and fiber photometry to measure calcium transients in real-time, we sought to characterize the spatial and temporal patterns of BLA activation in response to a range of novel stressors (shock, swim, restraint, predator odour) and non-aversive, but novel stimuli (crackers, citral odour). We report four main findings: (1) the BLA exhibits clear spatial activation gradients in response to novel stimuli throughout the medial-lateral and dorsal-ventral axes, with aversive stimuli strongly biasing activation towards medial aspects of the BLA; (2) novel stimuli elicit distinct temporal activation patterns, with stressful stimuli exhibiting particularly enhanced or prolonged temporal activation patterns; (3) changes in BLA activity are associated with changes in behavioural state; and (4) norepinephrine enhances stress-induced activation of BLA neurons via the ß-noradrenergic receptor. Moving forward, it will be imperative to combine our understanding of activation gradients with molecular and circuit-specificity.

An Honest Reckoning With the Amygdala and Mental Illness

Anxiety disorders are a leading source of human misery, morbidity, and premature mortality. Existing treatments are far from curative for many, underscoring the need to clarify the underlying neural mechanisms. Although many brain regions contribute, the amygdala has received the most intense scientific attention. Over the past several decades, this scrutiny has yielded a detailed understanding of amygdala function, but it has failed to produce new clinical assays, biomarkers, or cures. Rising to this urgent public health challenge demands an honest reckoning with the functional-neuroanatomical complexity of the amygdala and a shift from theories anchored on "the amygdala" to models centered on specific amygdala nuclei and cell types. This review begins by examining evidence from studies of rodents, monkeys, and humans for the "canonical model," the idea that the amygdala plays a central role in fear- and anxiety-related states, traits, and disorders. Next, the authors selectively highlight work indicating that the canonical model, while true, is overly simplistic and fails to adequately capture the actual state of the evidentiary record, the breadth of amygdala-associated functions and illnesses, or the complexity of the amygdala's functional architecture. The authors describe the implications of these facts for basic and clinical neuroimaging research. The review concludes with some general recommendations for grappling with the complexity of the amygdala and accelerating efforts to understand and more effectively treat amygdala-related psychopathology.

Makwana A, Gopalakrishna PK, Prameela Rani K, Vishnumukkala T. Unraveling the amygdala: A review of its anatomy and functions

The amygdala is a complex cellular structure situated centrally in the brain, adjacent to the hippocampus. It is an integral part of the limbic system and is essential for the processing of emotional reactions. The amygdala possesses extensive connections to multiple brain regions, enabling it to acquire sensory information and affect responses. The amygdaloid complex has over ten nuclei located in the mid-temporal lobe. It is quite likely that the primary root of certain anxiety disorders in humans, such as posttraumatic stress disorder, is a dysfunction in the processing of information associated with fear. This article analyzes the anatomical and physiological foundations suggested to support amygdala function.

How Distributed Subcortical Integration of Reward and Threat May Inform Subsequent Approach-Avoidance Decisions

Healthy and successful living involves carefully navigating rewarding and threatening situations by balancing approach and avoidance behaviors. Excessive avoidance to evade potential threats often leads to forfeiting potential rewards. However, little is known about how reward and threat information is integrated neurally to inform approach or avoidance. In this preregistered study, participants (N behavior = 31, 17F; N MRI = 28, 15F) made approach-avoidance decisions under varying reward (monetary gains) and threat (electrical stimulations) prospects during functional MRI scanning. In contrast to theorized parallel subcortical processing of reward and threat information before cortical integration, Bayesian multivariate multilevel analyses revealed subcortical reward and threat integration prior to indicating approach-avoidance decisions. This integration occurred in the ventral striatum, thalamus, and bed nucleus of the stria terminalis (BNST). When reward was low, risk-diminishing avoidance decisions dominated, which was linked to more positive tracking of threat magnitude prior to indicating avoidance than approach decisions. In contrast, the amygdala exhibited dual sensitivity to reward and threat. While anticipating outcomes of risky approach decisions, we observed positive tracking of threat magnitude within the salience network (dorsal anterior cingulate cortex, thalamus, periaqueductal gray, BNST). Conversely, after risk-diminishing avoidance, characterized by reduced reward prospects, we observed more negative tracking of reward magnitude in the ventromedial prefrontal cortex and ventral striatum. These findings shed light on the temporal dynamics of approach-avoidance decision-making. Importantly, they demonstrate the role of subcortical integration of reward and threat information in balancing approach and avoidance, challenging theories positing predominantly separate subcortical processing prior to cortical integration.

Developmental Shifts in Amygdala Function

Mammals have evolved with strategies to optimize survival and thrive in their native environment. This includes both physical and behavioral adaptations, and extends to their social environment. However, within a social context, the roles of an animal change across development, and their behavior and biology must update to match these changes. The amygdala has a key role in social and emotional processing and expression, and displays developmental changes in early juvenile, adolescent, and adult transitions. Furthermore, the amygdala is highly sensitive to the social environment. This chapter will describe the primary amygdala developmental changes, how this maps onto major changes in social and emotional domains, and propose a framework where developmental stage of intra-amygdala circuits and its regulation by cortical inputs biases the animal toward developmentally appropriate social and emotional behavior. This developmental plasticity also presents an opportunity for retuning the developmental trajectory in the presence of ongoing challenges during maturation, such as constant threat or resource scarcity, so there can be realignment of behavior to match environmental demands.

The interhemispheric amygdala-accumbens circuit encodes negative valence in mice

The structurally symmetric mammalian brain hemispheres are interconnected by commissural axons across the midline. However, the functions of interhemispheric connectivity remain largely unknown. We found that in mice, transection of the anterior commissure (AC), which connects the rostroventral forebrain, impaired avoidant behaviors. The basolateral amygdala (BLA) in the mouse projects to the contralateral nucleus accumbens (NAc) through the AC, independent of its ipsilateral projections. Aversive stimuli activated contralateral BLA-NAc projections. Positive stimuli, however, activated ipsilateral projections. Selective activation of contralateral BLA-NAc projections activated D2-positive medium spiny neurons (D2-MSNs), reduced NAc dopamine levels, and caused aversion, whereas selective activation of ipsilateral BLA-NAc projections activated D1-MSNs, increased NAc dopamine levels, and induced reward. The contralateral BLA-AC-NAc pathway is crucial for encoding negative valence, demonstrating distinct functions of intra- and interhemispheric circuits in brain physiology.

Acute stress activates basolateral amygdala neurons expressing corticotropin-releasing hormone receptor type 1 (CRHR1): Topographical distribution and projection-specific activation in male and female rats

Although the basolateral amygdala (BLA) and corticotropin releasing hormone receptor type I (CRHR1) signaling are both central to the stress response, the spatial and circuit-specific distribution of CRHR1 have not been identified in the BLA at a high resolution. We used transgenic male and female CRHR1-Cre-tdTomato rats to topographically map the distribution of BLACRHR1 neurons and identify whether they are activated by acute stress. Additionally, we used the BLA circuits projecting to the central amygdala (CeA) and nucleus accumbens (NAc) as a model to test circuit-specific expression of CRHR1 in the BLA. We established several key findings. First, CRHR1 had the strongest expression in the lateral amygdala and in caudal portions of the BLA. Second, acute restraint stress increased FOS expression of CRHR1 neurons, and stress-induced activation was particularly strong in medial subregions of the BLA. Third, stress significantly increased FOS expression on BLA-NAc, but not BLA-CeA projectors, and BLA-NAc activation was more robust in males than females. Finally, CRHR1 was expressed on a subset of BLA-CeA and BLA-NAc projection neurons. Collectively, this expands our understanding of BLA molecular- and circuit-specific activation patterns following acute stress.

Functional connectivity of the amygdala subnuclei in various mood states of bipolar disorder

Amygdala functional dysconnectivity lies at the heart of the pathophysiology of bipolar disorder (BD). Recent preclinical studies suggest that the amygdala is a heterogeneous group of nuclei, whose specific connectivity could drive positive or negative emotional valence. We investigated functional connectivity (FC) changes within these circuits emerging from each amygdala's subdivision in 127 patients with BD in different mood states and 131 healthy controls (HC), who underwent resting-state functional MRI. FC was evaluated between lateral and medial nuclei of amygdalae, and key subcortical regions of the emotion processing network: anterior and posterior parts of the hippocampus, and core and shell parts of the nucleus accumbens. FC was compared across groups, and subgroups of patients depending on their mood states, using linear mixed models. We also tested correlations between FC and depression (MADRS) and mania (YMRS) scores. We found no difference between the whole sample of BD patients vs. HC but a significant correlation between MADRS and right lateral amygdala /right anterior hippocampus, right lateral amygdala/right posterior hippocampus and right lateral amygdala/left anterior hippocampus FC (r = -0.44, r = -0.32, r = -0.27, respectively, all pFDR<0.05). Subgroup analysis revealed decreased right lateral amygdala/right anterior hippocampus and right lateral amygdala/right posterior hippocampus FC in depressed vs. non-depressed patients and increased left medial amygdala/shell part of the left nucleus accumbens FC in manic vs non-manic patients. These results demonstrate that acute mood states in BD concur with FC changes in individual nuclei of the amygdala implicated in distinct emotional valence processing. Overall, our data highlight the importance to consider the amygdala subnuclei separately when studying its FC patterns including patients in distinct homogeneous mood states.

Basolateral amygdala inputs to the nucleus accumbens shell modulate the consolidation of cued-response and inhibitory avoidance learning

The basolateral amygdala (BLA) modulates different types of memory consolidation via distinct projections to downstream brain regions in multiple memory systems. Prior studies indicate that the BLA projects to the nucleus accumbens shell (NAshell) and that these regions interact to influence some types of behavior. Moreover, previous pharmacological work suggests the BLA and NAshell interact to influence memory. However, the precise role of the BLA-NAshell pathway has never been directly investigated in the consolidation of different types of memory including cued-response, spatial, or inhibitory avoidance (IA) learning. To address this, male and female Sprague-Dawley rats received optogenetic manipulations of the BLA or BLA-NAshell pathway immediately following training in different learning tasks. An initial experiment found that optogenetically inhibiting the BLA itself immediately after training impaired cued-response retention in a Barnes maze task in males and females, confirming earlier pharmacological work in males alone. Subsequent experiments found that BLA-NAshell pathway inhibition impaired retention of cued-response and IA learning but had no effect on retention of spatial learning. However, the present work did not observe any effects of pathway stimulation immediately after cued-response or IA learning. Together, the present findings suggest the BLA modulates the consolidation of cued-response and IA, but not spatial, memory consolidation via NAshell projections.

Transformation of valence signaling in a mouse striatopallidal circuit

The ways in which sensory stimuli acquire motivational valence through association with other stimuli is one of the simplest forms of learning. Although we have identified many brain nuclei that play various roles in reward processing, a significant gap remains in understanding how valence encoding transforms through the layers of sensory processing. To address this gap, we carried out a comparative investigation of the mouse anteromedial olfactory tubercle (OT), and the ventral pallidum (VP) - 2 connected nuclei of the basal ganglia which have both been implicated in reward processing. First, using anterograde and retrograde tracing, we show that both D1 and D2 neurons of the anteromedial OT project primarily to the VP and minimally elsewhere. Using two-photon calcium imaging, we then investigated how the identity of the odor and reward contingency of the odor are differently encoded by neurons in either structure during a classical conditioning paradigm. We find that VP neurons robustly encode reward contingency, but not identity, in low-dimensional space. In contrast, the OT neurons primarily encode odor identity in high-dimensional space. Although D1 OT neurons showed larger responses to rewarded odors than other odors, consistent with prior findings, we interpret this as identity encoding with enhanced contrast. Finally, using a novel conditioning paradigm that decouples reward contingency and licking vigor, we show that both features are encoded by non-overlapping VP neurons. These results provide a novel framework for the striatopallidal circuit in which a high-dimensional encoding of stimulus identity is collapsed onto a low-dimensional encoding of motivational valence.

Control of innate olfactory valence by segregated cortical amygdala circuits

Animals exhibit innate behaviors that are stereotyped responses to specific evolutionarily relevant stimuli in the absence of prior learning or experience. These behaviors can be reduced to an axis of valence, whereby specific odors evoke approach or avoidance responses. The posterolateral cortical amygdala (plCoA) mediates innate attraction and aversion to odor. However, little is known about how this brain area gives rise to behaviors of opposing motivational valence. Here, we sought to define the circuit features of plCoA that give rise to innate attraction and aversion to odor. We characterized the physiology, gene expression, and projections of this structure, identifying a divergent, topographic organization that selectively controls innate attraction and avoidance to odor. First, we examined odor-evoked responses in these areas and found sparse encoding of odor identity, but not valence. We next considered a topographic organization and found that optogenetic stimulation of the anterior and posterior domains of plCoA elicits attraction and avoidance, respectively, suggesting a functional axis for valence. Using single cell and spatial RNA sequencing, we identified the molecular cell types in plCoA, revealing an anteroposterior gradient in cell types, whereby anterior glutamatergic neurons preferentially express VGluT2 and posterior neurons express VGluT1. Activation of these respective cell types recapitulates appetitive and aversive behaviors, and chemogenetic inhibition reveals partial necessity for responses to innate appetitive or aversive odors. Finally, we identified topographically organized circuits defined by projections, whereby anterior neurons preferentially project to medial amygdala, and posterior neurons preferentially project to nucleus accumbens, which are respectively sufficient and necessary for innate attraction and aversion. Together, these data advance our understanding of how the olfactory system generates stereotypic, hardwired attraction and avoidance, and supports a model whereby distinct, topographically distributed plCoA populations direct innate olfactory responses by signaling to divergent valence-specific targets, linking upstream olfactory identity to downstream valence behaviors, through a population code. This suggests a novel amygdala circuit motif in which valence encoding is represented not by the firing properties of individual neurons, but by population level identity encoding that is routed through divergent targets to mediate distinct behaviors of opposing appetitive and aversive responses.

Disrupted basolateral amygdala circuits supports negative valence bias in depressive states

Negative bias is an essential characteristic of depressive episodes leading patients to attribute more negative valence to environmental cues. This negative bias affects all levels of information processing including emotional response, attention and memory, leading to the development and maintenance of depressive symptoms. In this context, pleasant stimuli become less attractive and unpleasant ones more aversive, yet the related neural circuits underlying this bias remain largely unknown. By studying a mice model for depression chronically receiving corticosterone (CORT), we showed a negative bias in valence attribution to olfactory stimuli that responds to antidepressant drug. This result paralleled the alterations in odor value assignment we observed in bipolar depressed patients. Given the crucial role of amygdala in valence coding and its strong link with depression, we hypothesized that basolateral amygdala (BLA) circuits alterations might support negative shift associated with depressive states. Contrary to humans, where limits in spatial resolution of imaging tools impair easy amygdala segmentation, recently unravelled specific BLA circuits implicated in negative and positive valence attribution could be studied in mice. Combining CTB and rabies-based tracing with ex vivo measurements of neuronal activity, we demonstrated that negative valence bias is supported by disrupted activity of specific BLA circuits during depressive states. Chronic CORT administration induced decreased recruitment of BLA-to-NAc neurons preferentially involved in positive valence encoding, while increasing recruitment of BLA-to-CeA neurons preferentially involved in negative valence encoding. Importantly, this dysfunction was dampened by chemogenetic hyperactivation of BLA-to-NAc neurons. Moreover, altered BLA activity correlated with durable presynaptic connectivity changes coming from the paraventricular nucleus of the thalamus, recently demonstrated as orchestrating valence assignment in the amygdala. Together, our findings suggest that specific BLA circuits alterations might support negative bias in depressive states and provide new avenues for translational research to understand the mechanisms underlying depression and treatment efficacy.

State- and Circuit-Dependent Opponent Processing of Fear

The presence of valence coding neurons in the basolateral amygdala (BLA) that form distinct projections to other brain regions implies functional opposition between aversion and reward during learning. However, evidence for opponent interactions in fear learning is sparse and may only be apparent under certain conditions. Here we test this possibility by studying the roles of the BLA→central amygdala (CeA) and BLA→nucleus accumbens (Acb) pathways in fear learning in male rats. First, we assessed the organization of these pathways in the rat brain. BLA→CeA and BLA→Acb pathways were largely segregated in the BLA but shared overlapping molecular profiles. Then we assessed activity of the BLA→CeA and BLA→Acb pathways during two different forms of fear learning-fear learning in a neutral context and fear learning in a reward context. BLA→CeA neurons were robustly recruited by footshock regardless of where fear learning occurred, whereas recruitment of BLA→Acb neurons was state-dependent because footshock only recruited this pathway in a reward context. Finally, we assessed the causal roles of activity in these pathways in fear learning. Photoinhibition of the BLA→CeA pathway during the footshock US impaired fear learning, regardless of where fear learning occurred. In contrast, photoinhibition of the BLA→Acb pathway augmented fear learning, but only in the reward context. Taken together, our findings show circuit- and state-dependent opponent processing of fear. Footshock activity in the BLA→Acb pathway limits how much fear is learned.

Amygdala and Cortex Relationships during Learning of a Sensory Discrimination Task

During learning of a sensory discrimination task, the cortical and subcortical regions display complex spatiotemporal dynamics. During learning, both the amygdala and cortex link stimulus information to its appropriate association, for example, a reward. In addition, both structures are also related to nonsensory parameters such as body movements and licking during the reward period. However, the emergence of the cortico-amygdala relationships during learning is largely unknown. To study this, we combined wide-field cortical imaging with fiber photometry to simultaneously record cortico-amygdala population dynamics as male mice learn a whisker-dependent go/no-go task. We were able to simultaneously record neuronal populations from the posterior cortex and either the basolateral amygdala (BLA) or central/medial amygdala (CEM). Prior to learning, the somatosensory and associative cortex responded during sensation, while amygdala areas did not show significant responses. As mice became experts, amygdala responses emerged early during the sensation period, increasing in the CEM, while decreasing in the BLA. Interestingly, amygdala and cortical responses were associated with task-related body movement, displaying significant responses ∼200 ms before movement initiation which led to licking for the reward. A correlation analysis between the cortex and amygdala revealed negative and positive correlation with the BLA and CEM, respectively, only in the expert case. These results imply that learning induces an involvement of the cortex and amygdala which may aid to link sensory stimuli with appropriate associations.

Genetically- and spatially-defined basolateral amygdala neurons control food consumption and social interaction

The basolateral amygdala (BLA) contains discrete neuronal circuits that integrate positive or negative emotional information and drive the appropriate innate and learned behaviors. Whether these circuits consist of genetically-identifiable and anatomically segregated neuron types, is poorly understood. Also, our understanding of the response patterns and behavioral spectra of genetically-identifiable BLA neurons is limited. Here, we classified 11 glutamatergic cell clusters in mouse BLA and found that several of them were anatomically segregated in lateral versus basal amygdala, and anterior versus posterior regions of the BLA. Two of these BLA subpopulations innately responded to valence-specific, whereas one responded to mixed - aversive and social - cues. Positive-valence BLA neurons promoted normal feeding, while mixed selectivity neurons promoted fear learning and social interactions. These findings enhance our understanding of cell type diversity and spatial organization of the BLA and the role of distinct BLA populations in representing valence-specific and mixed stimuli.

Unraveling the Prefrontal Cortex-Basolateral Amygdala Pathway's Role on Schizophrenia's Cognitive Impairments: A Multimodal Study in Patients and Mouse Models

BACKGROUND AND HYPOTHESIS

This study investigated the role of the medial prefrontal cortex (mPFC)-basolateral amygdala (BLA) pathway in schizophrenia (SCZ)-related cognitive impairments using various techniques.

STUDY DESIGN

This study utilized clinical scales, magnetic resonance imaging, single-cell RNA sequencing, and optogenetics to investigate the mPFC-BLA pathway in SCZ patients. In the mouse model, 6-week-old methylazoxymethanol acetate-induced mice demonstrated significant cognitive deficits, which were addressed through stereotaxic injections of an adeno-associated viral vector to unveil the neural connection between the mPFC and BLA.

STUDY RESULTS

Significant disparities in brain volume and neural activity, particularly in the dorsolateral prefrontal cortex (DLPFC) and BLA regions, were found between SCZ patients and healthy controls. Additionally, we observed correlations indicating that reduced volumes of the DLPFC and BLA were associated with lower cognitive function scores. Activation of the mPFC-BLA pathway notably improved cognitive performance in the SCZ model mice, with the targeting of excitatory or inhibitory neurons alone failing to replicate this effect. Single-cell transcriptomic profiling revealed gene expression differences in excitatory and inhibitory neurons in the BLA of SCZ model mice. Notably, genes differentially expressed in the BLA of these model mice were also found in the blood exosomes of SCZ patients.

CONCLUSIONS

Our research provides a comprehensive understanding of the role of the PFC-BLA pathway in SCZ, underscoring its significance in cognitive impairment and offering novel diagnostic and therapeutic avenues. Additionally, our research highlights the potential of blood exosomal mRNAs as noninvasive biomarkers for SCZ diagnosis, underscoring the clinical feasibility and utility of this method.

Experience-dependent information routing through the basolateral amygdala shapes behavioral outcomes

It is well established that the basolateral amygdala (BLA) is an emotional processing hub that governs a diverse repertoire of behaviors. Selective engagement of a heterogeneous cell population in the BLA is thought to contribute to this flexibility in behavioral outcomes. However, whether this process is impacted by previous experiences that influence emotional processing remains unclear. Here we demonstrate that previous positive (enriched environment [EE]) or negative (chronic unpredictable stress [CUS]) experiences differentially influence the activity of populations of BLA principal neurons projecting to either the nucleus accumbens core or bed nucleus of the stria terminalis. Chemogenetic manipulation of these projection-specific neurons can mimic or occlude the effects of CUS and EE on behavioral outcomes to bidirectionally control avoidance behaviors and stress-induced helplessness. These data demonstrate that previous experiences influence the responsiveness of projection-specific BLA principal neurons, biasing information routing through the BLA, to drive divergent behavioral outcomes.

Transformation of valence signaling in a striatopallidal circuit

The ways in which sensory stimuli acquire motivational valence through association with other stimuli is one of the simplest forms of learning. Though we have identified many brain nuclei that play various roles in reward processing, a significant gap remains in understanding how valence encoding transforms through the layers of sensory processing. To address this gap, we carried out a comparative investigation of the anteromedial olfactory tubercle (OT), and the ventral pallidum (VP) - 2 connected nuclei of the basal ganglia which have both been implicated in reward processing. First, using anterograde and retrograde tracing, we show that both D1 and D2 neurons of the anteromedial OT project primarily to the VP and minimally elsewhere. Using 2-photon calcium imaging, we then investigated how the identity of the odor and reward contingency of the odor are differently encoded by neurons in either structure during a classical conditioning paradigm. We find that VP neurons robustly encode reward contingency, but not identity, in low-dimensional space. In contrast, the OT neurons primarily encode odor identity in high-dimensional space. Although D1 OT neurons showed larger responses to rewarded odors than other odors, consistent with prior findings, we interpret this as identity encoding with enhanced contrast. Finally, using a novel conditioning paradigm that decouples reward contingency and licking vigor, we show that both features are encoded by non-overlapping VP neurons. These results provide a novel framework for the striatopallidal circuit in which a high-dimensional encoding of stimulus identity is collapsed onto a low-dimensional encoding of motivational valence.

Fear, defense, and emotion: A neuroethological understanding of the negative valence research domain criteria

We describe the close correspondence between predatory imminence continuum theory (PICT) and the National Institute of Mental Health's Research Domain Criteria (RDoC) for negative valence. RDoC's negative valence constructs relate aversively motivated behavioral reactions to various levels of threat. PICT divides defensive responses into distinct modes that vary along a continuum of the psychological closeness of predatory threat. While there is a close correspondence between PICT modes and negative valence threat constructs, based on PICT, we describe some potential elaborations of RDoC constructs. Both have consonant views of fear and anxiety and provide explicit distinctions between these emotional states, relating them to specific defensive behaviors and functions. We describe recent data that causally implicate human subjective emotional states with amygdala activity, which is also critical for defensive behavior. We conclude that attention to neuroethological views of defense can advance our understanding of the etiology and treatment of anxiety and stress disorders. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

A failure to discriminate social from non-social touch at the circuit level may underlie social avoidance in autism

Social touch is critical for communication and to impart emotions and intentions. However, certain autistic individuals experience aversion to social touch, especially when it is unwanted. We used a novel social touch assay and Neuropixels probes to compare neural responses to social vs. non-social interactions in three relevant brain regions: vibrissal somatosensory cortex, tail of striatum, and basolateral amygdala. We find that wild type (WT) mice showed aversion to repeated presentations of an inanimate object but not of another mouse. Cortical neurons cared most about touch context (social vs. object) and showed a preference for social interactions, while striatal neurons changed their preference depending on whether mice could choose or not to interact. Amygdalar and striatal neurons were preferentially modulated by forced object touch, which was the most aversive. In contrast, the Fmr1 knockout (KO) model of autism found social and non-social interactions equally aversive and displayed more aversive facial expressions to social touch when it invaded their personal space. Importantly, when Fmr1 KO mice could choose to interact, neurons in all three regions did not discriminate social valence. Thus, a failure to differentially encode social from non-social stimuli at the circuit level may underlie social avoidance in autism.

Ventral Pallidum and Amygdala Cooperate to Restrain Reward Approach under Threat

Foraging decisions involve assessing potential risks and prioritizing food sources, which can be challenging when confronted with changing and conflicting circumstances. A crucial aspect of this decision-making process is the ability to actively overcome defensive reactions to threats and focus on achieving specific goals. The ventral pallidum (VP) and basolateral amygdala (BLA) are two brain regions that play key roles in regulating behavior motivated by either rewards or threats. However, it is unclear whether these regions are necessary in decision-making processes involving competing motivational drives during conflict. Our aim was to investigate the requirements of the VP and BLA for foraging choices in conflicts involving overcoming defensive responses. Here, we used a novel foraging task and pharmacological techniques to inactivate either the VP or BLA or to disconnect these brain regions before conducting a conflict test in male rats. Our findings showed that BLA is necessary for making risky choices during conflicts, whereas VP is necessary for invigorating the drive to obtain food, regardless of the presence of conflict. Importantly, our research revealed that the connection between VP and BLA is critical in controlling risky food-seeking choices during conflict situations. This study provides a new perspective on the collaborative function of VP and BLA in driving behavior, aimed at achieving goals in the face of dangers.

The emotion paradox in the aging body and brain

With age, parasympathetic activity decreases, while sympathetic activity increases. Thus, the typical older adult has low heart rate variability (HRV) and high noradrenaline levels. Younger adults with this physiological profile tend to be unhappy and stressed. Yet, with age, emotional experience tends to improve. Why does older adults' emotional well-being not suffer as their HRV decreases? To address this apparent paradox, I present the autonomic compensation model. In this model, failing organs, the initial phases of Alzheimer's pathology, and other age-related diseases trigger noradrenergic hyperactivity. To compensate, older brains increase autonomic regulatory activity in the pregenual prefrontal cortex (PFC). Age-related declines in nerve conduction reduce the ability of the pregenual PFC to reduce hyperactive noradrenergic activity and increase peripheral HRV. But these pregenual PFC autonomic compensation efforts have a significant impact in the brain, where they bias processing in favor of stimuli that tend to increase parasympathetic activity (e.g., stimuli that increase feelings of safety) and against stimuli that tend to increase sympathetic activity (e.g., threatening stimuli). In summary, the autonomic compensation model posits that age-related chronic sympathetic/noradrenergic hyperactivity stimulates regulatory attempts that have the side effect of enhancing emotional well-being.

Synergism between two BLA-to-BNST pathways for appropriate expression of anxiety-like behaviors in male mice

Understanding how distinct functional circuits are coordinated to fine-tune mood and behavior is of fundamental importance. Here, we observe that within the dense projections from basolateral amygdala (BLA) to bed nucleus of stria terminalis (BNST), there are two functionally opposing pathways orchestrated to enable contextually appropriate expression of anxiety-like behaviors in male mice. Specifically, the anterior BLA neurons predominantly innervate the anterodorsal BNST (adBNST), while their posterior counterparts send massive fibers to oval BNST (ovBNST) with moderate to adBNST. Optogenetic activation of the anterior and posterior BLA inputs oppositely regulated the activity of adBNST neurons and anxiety-like behaviors, via disengaging and engaging the inhibitory ovBNST-to-adBNST microcircuit, respectively. Importantly, the two pathways exhibited synchronized but opposite responses to both anxiolytic and anxiogenic stimuli, partially due to their mutual inhibition within BLA and the different inputs they receive. These findings reveal synergistic interactions between two BLA-to-BNST pathways for appropriate anxiety expression with ongoing environmental demands.

The representational geometry of emotional states in basolateral amygdala

Sensory stimuli associated with aversive outcomes cause multiple behavioral responses related to an animal's evolving emotional state, but neural mechanisms underlying these processes remain unclear. Here aversive stimuli were presented to mice, eliciting two responses reflecting fear and flight to safety: tremble and ingress into a virtual burrow. Inactivation of basolateral amygdala (BLA) eliminated differential responses to aversive and neutral stimuli without eliminating responses themselves, suggesting BLA signals valence, not motor commands. However, two-photon imaging revealed that neurons typically exhibited mixed selectivity for stimulus identity, valence, tremble and/or ingress. Despite heterogeneous selectivity, BLA representational geometry was lower-dimensional when encoding valence, tremble and safety, enabling generalization of emotions across conditions. Further, tremble and valence coding directions were orthogonal, allowing linear readouts to specialize. Thus BLA representational geometry confers two computational properties that identify specialized neural circuits encoding variables describing emotional states: generalization across conditions, and readouts lacking interference from other readouts.

Pathophysiology in cortico-amygdala circuits and excessive aversion processing: the role of oligodendrocytes and myelination

Stress-related psychiatric illnesses, such as major depressive disorder, anxiety and post-traumatic stress disorder, present with alterations in emotional processing, including excessive processing of negative/aversive stimuli and events. The bidirectional human/primate brain circuit comprising anterior cingulate cortex and amygdala is of fundamental importance in processing emotional stimuli, and in rodents the medial prefrontal cortex-amygdala circuit is to some extent analogous in structure and function. Here, we assess the comparative evidence for: (i) Anterior cingulate/medial prefrontal cortex<->amygdala bidirectional neural circuits as major contributors to aversive stimulus processing; (ii) Structural and functional changes in anterior cingulate cortex<->amygdala circuit associated with excessive aversion processing in stress-related neuropsychiatric disorders, and in medial prefrontal cortex<->amygdala circuit in rodent models of chronic stress-induced increased aversion reactivity; and (iii) Altered status of oligodendrocytes and their oligodendrocyte lineage cells and myelination in anterior cingulate/medial prefrontal cortex<->amygdala circuits in stress-related neuropsychiatric disorders and stress models. The comparative evidence from humans and rodents is that their respective anterior cingulate/medial prefrontal cortex<->amygdala circuits are integral to adaptive aversion processing. However, at the sub-regional level, the anterior cingulate/medial prefrontal cortex structure-function analogy is incomplete, and differences as well as similarities need to be taken into account. Structure-function imaging studies demonstrate that these neural circuits are altered in both human stress-related neuropsychiatric disorders and rodent models of stress-induced increased aversion processing. In both cases, the changes include altered white matter integrity, albeit the current evidence indicates that this is decreased in humans and increased in rodent models. At the cellular-molecular level, in both humans and rodents, the current evidence is that stress disorders do present with changes in oligodendrocyte lineage, oligodendrocytes and/or myelin in these neural circuits, but these changes are often discordant between and even within species. Nonetheless, by integrating the current comparative evidence, this review provides a timely insight into this field and should function to inform future studies-human, monkey and rodent-to ascertain whether or not the oligodendrocyte lineage and myelination are causally involved in the pathophysiology of stress-related neuropsychiatric disorders.

Review of EEG Affective Recognition with a Neuroscience Perspective

Emotions are a series of subconscious, fleeting, and sometimes elusive manifestations of the human innate system. They play crucial roles in everyday life-influencing the way we evaluate ourselves, our surroundings, and how we interact with our world. To date, there has been an abundance of research on the domains of neuroscience and affective computing, with experimental evidence and neural network models, respectively, to elucidate the neural circuitry involved in and neural correlates for emotion recognition. Recent advances in affective computing neural network models often relate closely to evidence and perspectives gathered from neuroscience to explain the models. Specifically, there has been growing interest in the area of EEG-based emotion recognition to adopt models based on the neural underpinnings of the processing, generation, and subsequent collection of EEG data. In this respect, our review focuses on providing neuroscientific evidence and perspectives to discuss how emotions potentially come forth as the product of neural activities occurring at the level of subcortical structures within the brain's emotional circuitry and the association with current affective computing models in recognizing emotions. Furthermore, we discuss whether such biologically inspired modeling is the solution to advance the field in EEG-based emotion recognition and beyond.

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.

Cholinergic Basal Forebrain Connectivity to the Basolateral Amygdala Modulates Food Intake

Obesity results from excessive caloric input associated with overeating and presents a major public health challenge. The hypothalamus has received significant attention for its role in governing feeding behavior and body weight homeostasis. However, extrahypothalamic brain circuits also regulate appetite and consumption by altering sensory perception, motivation, and reward. We recently discovered a population of basal forebrain cholinergic (BFc) neurons that regulate appetite suppression. Through viral tracing methods in the mouse model, we found that BFc neurons densely innervate the basolateral amygdala (BLA), a limbic structure involved in motivated behaviors. Using channelrhodopsin-assisted circuit mapping, we identified cholinergic responses in BLA neurons following BFc circuit manipulations. Furthermore, in vivo acetylcholine sensor and genetically encoded calcium indicator imaging within the BLA (using GACh3 and GCaMP, respectively) revealed selective response patterns of activity during feeding. Finally, through optogenetic manipulations in vivo, we found that increased cholinergic signaling from the BFc to the BLA suppresses appetite and food intake. Together, these data support a model in which cholinergic signaling from the BFc to the BLA directly influences appetite and feeding behavior.

Basolateral amygdala neuropeptide Y system modulates binge ethanol consumption

Neuropeptide Y (NPY) signaling regulation of corticolimbic communication is known to modulate binge-like ethanol consumption in rodents. In this work we sought to assess the impact of intra-BLA NPY system modulation on binge-like ethanol intake and to assess the role of the NPY1R+ projection from the BLA to the mPFC in this behavior. We used "drinking-in-the-dark" (DID) procedures in C57BL6J mice to address these questions. First, the impact of intra-BLA administration of NPY on binge-like ethanol intake was assessed. Next, the impact of repeated cycles of DID intake on NPY1R expression in the BLA was assessed with use of immunohistochemistry (IHC). Finally, chemogenetic inhibition of BLA→mPFC NPY1R+ projections was assessed to determine if limbic communication with the mPFC was specifically involved in binge-like ethanol intake. Importantly, as both the BLA and NPY system are sexually dimorphic, both sexes were assessed in these studies. Intra-BLA NPY dose-dependently decreased binge-like ethanol intake in males only. Repeated DID reduced NPY1R expression in the BLA of both sexes. Silencing of BLA→mPFC NPY1R+ neurons significantly reduced binge-like ethanol intake in both sexes in a dose-dependent manner. We provide novel evidence that (1) intra-BLA NPY reduces binge-like ethanol intake in males; (2) binge-like ethanol intake reduces NPY1R levels in the BLA; and (3) chemogenetic inhibition of BLA→mPFC NPY1R+ neurons blunts binge-like drinking in male and female mice. These observations provide the first direct evidence that NPY signaling in the BLA, and specifically BLA communication with the mPFC, modulates binge-like ethanol consumption.

Perineuronal net structure as a non-cellular mechanism contributing to affective state: A scoping review

Affective state encompasses emotional responses to our physiology and influences how we perceive and respond within our environment. In affective disorders such as depression, cognitive adaptability is challenged, and structural and functional brain changes have been identified. However, an incomplete understanding persists of the molecular and cellular mechanisms at play in affective state. An exciting area of newly appreciated importance is perineuronal nets (PNNs); a specialised component of extracellular matrix playing a critical role in neuroprotection and synaptic plasticity. A scoping review found 24 studies demonstrating that PNNs are still a developing field of research with a promising general trend for stress in adulthood to increase the intensity of PNNs, whereas stress in adolescence reduced (potentially developmentally delayed) PNN numbers and intensity, while antidepressants correlated with reduced PNN numbers. Despite promising trends, limited research underscores the need for further exploration, emphasizing behavioral outcomes for validating affective states. Understanding PNNs' role may offer therapeutic insights for depression and inform biomarker development, advancing precision medicine and enhancing well-being.

Engagement of basal amygdala-nucleus accumbens glutamate neurons in the processing of rewarding or aversive social stimuli

Basal amygdala (BA) neurons projecting to nucleus accumbens (NAc) core/shell are primarily glutamatergic and are integral to the circuitry of emotional processing. Several recent mouse studies have addressed whether neurons in this population(s) respond to reward, aversion or both emotional valences. The focus has been on processing of physical emotional stimuli, and here, we extend this to salient social stimuli. In male mice, an iterative study was conducted into engagement of BA-NAc neurons in response to estrous female (social reward, SR) and/or aggressive-dominant male (social aversion, SA). In BL/6J mice, SR and SA activated c-Fos expression in a high and similar number/density of BA-NAc neurons in the anteroposterior intermediate BA (int-BA), whereas activation was predominantly by SA in posterior (post-)BA. In Fos-TRAP2 mice, compared with SR-SR or SA-SA controls, exposure to successive presentation of SR-SA or SA-SR, followed by assessment of tdTomato reporter and/or c-Fos expression, demonstrated that many int-BA-NAc neurons were activated by only one of SR and SA; these SR/SA monovalent neurons were similar in number and present in both magnocellular and parvocellular int-BA subregions. In freely moving BL/6J mice exposed to SR, bulk GCaMP6 fibre photometry provided confirmatory in vivo evidence for engagement of int-BA-NAc neurons during social and sexual interactions. Therefore, populations of BA-NAc glutamate neurons are engaged by salient rewarding and aversive social stimuli in a topographic and valence-specific manner; this novel evidence is important to the overall understanding of the roles of this pathway in the circuitry of socio-emotional processing.

Driving valence-specific behavior through single-cell resolution control in the amygdala

In this issue of Neuron, Piantadosi et al.1 demonstrate that by precisely controlling the activity of individual negative-valence neurons and positive-valence neurons in the basolateral amygdala, one can alter animals' appetitive or aversive responses, respectively, establishing a causal role of these neurons in valence-specific behavior.

Holographic stimulation of opposing amygdala ensembles bidirectionally modulates valence-specific behavior via mutual inhibition

The basolateral amygdala (BLA) is an evolutionarily conserved brain region, well known for valence processing. Despite this central role, the relationship between activity of BLA neuronal ensembles in response to appetitive and aversive stimuli and the subsequent expression of valence-specific behavior has remained elusive. Here, we leverage two-photon calcium imaging combined with single-cell holographic photostimulation through an endoscopic lens to demonstrate a direct causal role for opposing ensembles of BLA neurons in the control of oppositely valenced behavior in mice. We report that targeted photostimulation of either appetitive or aversive BLA ensembles results in mutual inhibition and shifts behavioral responses to promote consumption of an aversive tastant or reduce consumption of an appetitive tastant, respectively. Here, we identify that neuronal encoding of valence in the BLA is graded and relies on the relative proportion of individual BLA neurons recruited in a stable appetitive or quinine ensemble.

Updating the striatal-pallidal wiring diagram

The striatal and pallidal complexes are basal ganglia structures that orchestrate learning and execution of flexible behavior. Models of how the basal ganglia subserve these functions have evolved considerably, and the advent of optogenetic and molecular tools has shed light on the heterogeneity of subcircuits within these pathways. However, a synthesis of how molecularly diverse neurons integrate into existing models of basal ganglia function is lacking. Here, we provide an overview of the neurochemical and molecular diversity of striatal and pallidal neurons and synthesize recent circuit connectivity studies in rodents that takes this diversity into account. We also highlight anatomical organizational principles that distinguish the dorsal and ventral basal ganglia pathways in rodents. Future work integrating the molecular and anatomical properties of striatal and pallidal subpopulations may resolve controversies regarding basal ganglia network function.

The modulation effects of the mind-body and physical exercises on the basolateral amygdala-temporal pole pathway on individuals with knee osteoarthritis

Background/Objective

To investigate the modulatory effects of different physical exercise modalities on connectivity of amygdala subregions and its association with pain symptoms in patients with knee osteoarthritis (KOA).

Methods

140 patients with KOA were randomly allocated either to the Tai Chi, Baduanjin, Stationary cycling, or health education group and conducted a 12 week-long intervention in one of the four groups. The behavioral, magnetic resonance imaging (MRI), and blood data were collected at baseline and the end of the study.

Results

Compared to the control group, all physical exercise modalities lead to significant increases in Knee Injury and Osteoarthritis Outcome Score (KOOS) pain score (pain relief) and serum Programmed Death-1 (PD-1) levels. Additionally, all physical exercise modalities resulted in decreased resting state functional connectivity (rsFC) of the basolateral amygdala (BA)-temporal pole and BA-medial prefrontal cortex (mPFC). The overlapping BA-temporal pole rsFC observed in both Tai Chi and Baduanjin groups was significantly associated with pain relief, while the BA-mPFC rsFC was significantly associated with PD-1 levels. In addition, we found increased fractional anisotropy (FA) values, a measurement of water diffusion anisotropy of tissue that responded to changes in brain microstructure, within the mind-body exercise groups' BA-temporal pole pathway. The average FA value of this pathway was positively correlated with KOOS pain score at baseline across all subjects.

Conclusions

Our findings suggest that physical exercise has the potential to modulate both functional and anatomical connectivity of the amygdala subregions, indicating a possible shared pathway for various physical exercise modalities.

Neuronal types in the mouse amygdala and their transcriptional response to fear conditioning

The amygdala is a brain region primarily associated with emotional response. The use of genetic markers and single-cell transcriptomics can provide insights into behavior-associated cell state changes. Here we present a detailed cell-type taxonomy of the adult mouse amygdala during fear learning and memory consolidation. We perform single-cell RNA sequencing on naïve and fear-conditioned mice, identify 130 neuronal cell types and validate their spatial distributions. A subset of all neuronal types is transcriptionally responsive to fear learning and memory retrieval. The activated engram cells upregulate activity-response genes and coordinate the expression of genes associated with neurite outgrowth, synaptic signaling, plasticity and development. We identify known and previously undescribed candidate genes responsive to fear learning. Our molecular atlas may be used to generate hypotheses to unveil the neuron types and neural circuits regulating the emotional component of learning and memory.

A novel perspective on the role of nucleus accumbens neurons in encoding associative learning

The nucleus accumbens (NAc) has been considered a key brain region for encoding reward/aversion and cue-outcome associations. These processes are encoded by medium spiny neurons that express either dopamine receptor D1 (D1-MSNs) or D2 (D2-MSNs). Despite the well-established role of NAc neurons in encoding reward/aversion, the underlying processing by D1-/D2-MSNs remains largely unknown. Recent electrophysiological, optogenetic and calcium imaging studies provided insight on the complex role of D1- and D2-MSNs in these behaviours and helped to clarify their involvement in associative learning. Here, we critically discuss findings supporting an intricate and complementary role of NAc D1- and D2-MSNs in associative learning, emphasizing the need for additional studies in order to fully understand the role of these neurons in behaviour.

An amygdala-to-cingulate cortex circuit for conflicting choices in chronic pain

Chronic pain is a complex experience with multifaceted behavioral manifestations, often leading to pain avoidance at the expense of reward approach. How pain facilitates avoidance in situations with mixed outcomes is unknown. The anterior cingulate cortex (ACC) plays a key role in pain processing and in value-based decision-making. Distinct ACC inputs inform about the sensory and emotional quality of pain. However, whether specific ACC circuits underlie pathological conflict assessment in pain remains underexplored. Here, we demonstrate that mice with chronic pain favor cold avoidance rather than reward approach in a conflicting task. This occurs along with selective strengthening of basolateral amygdala inputs onto ACC layer 2/3 pyramidal neurons. The amygdala-cingulate projection is necessary and sufficient for the conflicting cold avoidance. Further, low-frequency stimulation of this pathway restores AMPA receptor function and reduces avoidance in pain mice. Our findings provide insights into the circuits and mechanisms underlying cognitive aspects of pain and offer potential targets for treatment.

The thalamic reticular nucleus-lateral habenula circuit regulates depressive-like behaviors in chronic stress and chronic pain

Chronic stress and chronic pain are two major predisposing factors to trigger depression. Enhanced excitatory input to the lateral habenula (LHb) has been implicated in the pathophysiology of depression. However, the contribution of inhibitory transmission remains unclear. Here, we dissect an inhibitory projection from the sensory thalamic reticular nucleus (sTRN) to the LHb, which is activated by acute aversive stimuli. However, chronic restraint stress (CRS) weakens sTRN-LHb synaptic strength, and this synaptic attenuation is indispensable for CRS-induced LHb neural hyperactivity and depression onset. Moreover, artificially inhibiting the sTRN-LHb circuit induces depressive-like behaviors in healthy mice, while enhancing this circuit relieves depression induced by both chronic stress and chronic pain. Intriguingly, neither neuropathic pain nor comorbid mechanical hypersensitivity in chronic stress is affected by this pathway. Altogether, our study demonstrates an sTRN-LHb circuit in establishing and modulating depression, thus shedding light on potential therapeutic targets for preventing or managing depression.