Central role for the insular cortex in mediating conditioned responses to anticipatory cues

Could Relationship-Based Learnt Beliefs and Expectations Contribute to Physiological Vulnerability of Chronic Pain? Making a Case to Consider Attachment in Pain Research

Pain is an interpersonal and inherently social experience. Pain perception and administration of medical treatment all occur in a particular environmental and social context. Early environmental influences and early learning experiences and interactions condition the body's response to different threats (like pain), ultimately shaping the underlying neurophysiology. These early interactions and experiences also determine what situations are perceived as threatening, as well as our belief in our own ability to self-manage, and our belief in others to offer support, during perceived threats. These beliefs intrinsically drive the combination of behaviors that emerge in response to perceived threats, including pain. Such behaviors can be categorized into attachment styles. In this interdisciplinary review, we synthesize and summarize evidence from the neurobiological, psychobiological, psychosocial, and psychobehavioral fields, to describe how these beliefs are embedded in the brain's prediction models to generate a series of expectations/perceptions around the level of safety/threat in different contexts. As such, these beliefs may predict how one experiences and responds to pain, with potentially significant implications for the development and management of chronic pain. Little attention has been directed to the effect of adult attachment style on pain in research studies and in the clinical setting. Using interdisciplinary evidence, we argue why we think this interaction merits further consideration and research. PERSPECTIVE: This review explores the influence of attachment styles on pain perception, suggesting a link between social connections and chronic pain development. It aligns with recent calls to emphasize the social context in pain research and advocates for increased focus on adult attachment styles in research and clinical practice.

Brain-body physiology: Local, reflex, and central communication

Behavior is tightly synchronized with bodily physiology. Internal needs from the body drive behavior selection, while optimal behavior performance requires a coordinated physiological response. Internal state is dynamically represented by the nervous system to influence mood and emotion, and body-brain signals also direct responses to external sensory cues, enabling the organism to adapt and pursue its goals within an ever-changing environment. In this review, we examine the anatomy and function of the brain-body connection, manifested across local, reflex, and central regulation levels. We explore these hierarchical loops in the context of the immune system, specifically through the lens of immunoception, and discuss the impact of its dysregulation on human health.

Neural Processing of Taste-Related Signals in the Mediodorsal Thalamus of Mice

Our consummatory decisions depend on the taste of food and the reward experienced while eating, which are processed through neural computations in interconnected brain areas. Although many gustatory regions of rodents have been explored, the mediodorsal nucleus of the thalamus (MD) remains understudied. The MD, a multimodal brain area connected with gustatory centers, is often studied for its role in processing associative and cognitive information and has been shown to represent intraorally-delivered chemosensory stimuli after strong retronasal odor-taste associations. Key questions remain about whether MD neurons can process taste quality independently of odor-taste associations and how they represent extraoral signals predicting rewarding and aversive gustatory outcomes. Here, we present electrophysiological evidence demonstrating how mouse MD neurons represent and encode 1) the identity and concentrations of basic taste qualities during active licking, and 2) auditory signals anticipating rewarding and aversive taste outcomes. Our data reveal that MD neurons can reliably and dynamically encode taste identity in a broadly tuned manner and taste concentrations with spiking activity positively and negatively correlated with stimulus intensity. Our data also show that MD can represent information related to predictive cues and their associated outcomes, regardless of whether the cue predicts a rewarding or aversive outcome. In summary, our findings suggest that the mediodorsal thalamus is integral to the taste pathway, as it can encode sensory-discriminative dimensions of tastants and participate in processing associative information essential for ingestive behaviors.

Electrophysiological responses to appetitive and consummatory behavior in the rostral nucleus tractus solitarius in awake, unrestrained rats

Introduction

As the intermediate nucleus in the brainstem receiving information from the tongue and transmitting information upstream, the rostral portion of the nucleus tractus solitarius (rNTS) is most often described as a "taste relay". Although recent evidence implicates the caudal NTS in a broad neural circuit involved in regulating ingestion, there is little information about how cells in the rNTS respond when an animal is eating solid food.

Methods

Single cells in the rNTS were recorded in awake, unrestrained rats as they explored and ate solid foods (Eating paradigm) chosen to correspond to the basic taste qualities: milk chocolate for sweet, salted peanuts for salty, Granny Smith apples for sour and broccoli for bitter. A subset of cells was also recorded as the animal licked exemplars of the five basic taste qualities: sucrose, NaCl, citric acid, quinine and MSG (Lick paradigm).

Results

Most cells were excited by exploration of a food-filled well, sometimes responding prior to contact with the food. In contrast, cells that were excited by food well exploration became significantly less active while the animal was eating the food. Most cells were broadly tuned across foods, and those cells that were recorded in both the Lick and Eating paradigms showed little correspondence in their tuning across paradigms.

Discussion

The preponderance of robust responses to the appetitive versus the consummatory phase of ingestion suggests that multimodal convergence onto cells in the rNTS may be used in decision making about ingestion.

Top-down brain circuits for operant bradycardia

Heart rate (HR) can be voluntarily regulated when individuals receive real-time feedback. In a rat model of HR biofeedback, the neocortex and medial forebrain bundle were stimulated as feedback and reward, respectively. The rats reduced their HR within 30 minutes, achieving a reduction of approximately 50% after 5 days of 3-hour feedback. The reduced HR persisted for at least 10 days after training while the rats exhibited anxiolytic behavior and an elevation in blood erythrocyte count. This bradycardia was prevented by inactivating anterior cingulate cortical (ACC) neurons projecting to the ventromedial thalamic nucleus (VMT). Theta-rhythm stimulation of the ACC-to-VMT pathway replicated the bradycardia. VMT neurons projected to the dorsomedial hypothalamus (DMH) and DMH neurons projected to the nucleus ambiguus, which innervates parasympathetic neurons in the heart.

Multisensory Integration Underlies the Distinct Representation of Odor-Taste Mixtures in the Gustatory Cortex of Behaving Rats

The perception of food relies on the integration of olfactory and gustatory signals originating from the mouth. This multisensory process generates robust associations between odors and tastes, significantly influencing the perceptual judgment of flavors. However, the specific neural substrates underlying this integrative process remain unclear. Previous electrophysiological studies identified the gustatory cortex as a site of convergent olfactory and gustatory signals, but whether neurons represent multimodal odor-taste mixtures as distinct from their unimodal odor and taste components is unknown. To investigate this, we recorded single-unit activity in the gustatory cortex of behaving female rats during the intraoral delivery of individual odors, individual tastes, and odor-taste mixtures. Our results demonstrate that chemoselective neurons in the gustatory cortex are broadly responsive to intraoral chemosensory stimuli, exhibiting time-varying multiphasic changes in activity. In a subset of these chemoselective neurons, odor-taste mixtures elicit nonlinear cross-modal responses that distinguish them from their olfactory and gustatory components. These findings provide novel insights into multimodal chemosensory processing by the gustatory cortex, highlighting the distinct representation of unimodal and multimodal intraoral chemosensory signals. Overall, our findings suggest that olfactory and gustatory signals interact nonlinearly in the gustatory cortex to enhance the identity coding of both unimodal and multimodal chemosensory stimuli.

Insular and prelimbic cortices control behavioral accuracy and precision in a temporal decision-making task in rats

The anterior insular cortex (AIC) comprises a region of sensory integration. It appears to detect salient events in order to guide goal-directed behavior, code tracking errors, and estimate the passage of time. Temporal processing in the AIC may be instantiated by the integration of representations of interoception. Projections between the AIC and the medial prefrontal cortex (mPFC) - found both in rats and humans - also suggest a possible role for these structures in the integration of autonomic responses during ongoing behavior. Few studies, however, have investigated the role of AIC and mPFC in decision-making and time estimation tasks. Moreover, their findings are not consistent, so the relationship between temporal decision-making and those areas remains unclear. The present study employed bilateral inactivations to explore the role of AIC and prelimbic cortex (PL) in rats during a temporal decision-making task. In this task, two levers are available simultaneously (but only one is active), one predicting reinforcement after a short, and the other after a long-fixed interval. Optimal performance requires a switch from the short to the long lever after the short-fixed interval elapsed and no reinforcement was delivered. Switch behavior from the short to the long lever was dependent on AIC and PL. During AIC inactivation, switch latencies became more variable, while during PL inactivation switch latencies became both more variable and less accurate. These findings point to a dissociation between AIC and PL in temporal decision-making, suggesting that the AIC is important for temporal precision, and PL is important for both temporal accuracy and precision.

Electrophysiological responses to appetitive and consummatory behavior in the rostral nucleus tractus solitarius in awake, unrestrained rats

As the intermediate nucleus in the brainstem receiving information from the tongue and transmitting information upstream, the rostral portion of the nucleus tractus solitarius (rNTS) is most often described as a "taste relay". Although recent evidence implicates the NTS in a broad neural circuit involved in regulating ingestion, there is little information about how cells in this structure respond when an animal is eating solid food. Here, single cells in the rNTS were recorded in awake, unrestrained rats as they explored and ate solid foods (Eating paradigm) chosen to correspond to the basic taste qualities: milk chocolate for sweet, salted peanuts for salty, Granny Smith apples for sour and broccoli for bitter. A subset of cells was also recorded as the animal licked exemplars of the five basic taste qualities: sucrose, NaCl, citric acid, quinine and MSG (Lick paradigm). Results showed that most cells were excited by exploration of a food-filled well, sometimes responding prior to contact with the food. In contrast, cells that were excited by food well exploration became significantly less active while the animal was eating the food. Most cells were broadly tuned across foods, and those cells that were recorded in both the Lick and Eating paradigms showed little correspondence in their tuning across paradigms. The preponderance of robust responses to the appetitive versus the consummatory phase of ingestion suggests that multimodal convergence onto cells in the rNTS may be used in decision making about ingestion.

Stereotyped goal-directed manifold dynamics in the insular cortex

The insular cortex is involved in diverse processes, including bodily homeostasis, emotions, and cognition. However, we lack a comprehensive understanding of how it processes information at the level of neuronal populations. We leveraged recent advances in unsupervised machine learning to study insular cortex population activity patterns (i.e., neuronal manifold) in mice performing goal-directed behaviors. We find that the insular cortex activity manifold is remarkably consistent across different animals and under different motivational states. Activity dynamics within the neuronal manifold are highly stereotyped during rewarded trials, enabling robust prediction of single-trial outcomes across different mice and across various natural and artificial motivational states. Comparing goal-directed behavior with self-paced free consumption, we find that the stereotyped activity patterns reflect task-dependent goal-directed reward anticipation, and not licking, taste, or positive valence. These findings reveal a core computation in insular cortex that could explain its involvement in pathologies involving aberrant motivations.

The neural representations of valence transformation in indole processing

Indole is often associated with a sweet and floral odor typical of jasmine flowers at low concentrations and an unpleasant, animal-like odor at high concentrations. However, the mechanism whereby the brain processes this opposite valence of indole is not fully understood yet. In this study, we aimed to investigate the neural mechanisms underlying indole valence encoding in conversion and nonconversion groups using the smelling task to arouse pleasantness. For this purpose, 12 conversion individuals and 15 nonconversion individuals participated in an event-related functional magnetic resonance imaging paradigm with low (low-indole) and high (high-indole) indole concentrations in which valence was manipulated independent of intensity. The results of this experiment showed that neural activity in the right amygdala, orbitofrontal cortex and insula was associated with valence independent of intensity. Furthermore, activation in the right orbitofrontal cortex in response to low-indole was positively associated with subjective pleasantness ratings. Conversely, activation in the right insula and amygdala in response to low-indole was positively correlated with anticipatory hedonic traits. Interestingly, while amygdala activation in response to high-indole also showed a positive correlation with these hedonic traits, such correlation was observed solely with right insula activation in response to high-indole. Additionally, activation in the right amygdala in response to low-indole was positively correlated with consummatory pleasure and hedonic traits. Regarding olfactory function, only activation in the right orbitofrontal cortex in response to high-indole was positively correlated with olfactory identification, whereas activation in the insula in response to low-indole was negatively correlated with the level of self-reported olfactory dysfunction. Based on these findings, valence transformation of indole processing in the right orbitofrontal cortex, insula, and amygdala may be associated with individual hedonic traits and perceptual differences.

Motivated cognitive control during cued anticipation and receipt of unfamiliar musical themes: An fMRI study

Principal themes, particularly choruses in pop songs, hold a central place in human music. Singing along with a familiar chorus tends to elicit pleasure and a sense of belonging, especially in group settings. These principal themes, which frequently serve as musical rewards, are commonly preceded by distinctive musical cues. Such cues guide listeners' attention and amplify their motivation to receive the impending themes. Despite the significance of cue-theme sequences in music, the neural mechanisms underlying the processing of these sequences in unfamiliar songs remain underexplored. To fill this research gap, we employed fMRI to examine neural activity during the cued anticipation of unfamiliar musical themes and the subsequent receipt of their opening phrase. Twenty-three Taiwanese participants underwent fMRI scans while listening to excerpts of Korean slow pop songs unfamiliar to them, with lyrics they could not understand. Our findings revealed distinct temporal dynamics in lateral frontal activity, with posterior regions being more active during theme anticipation and anterior regions during theme receipt. During anticipation, participants reported substantial increases in arousal levels, aligning with the observed enhanced activity in the midbrain, ventral striatum, inferior frontal junction, and premotor regions. We posit that when motivational musical cues are detected, the ventral striatum and inferior frontal junction played a role in attention allocation, while premotor regions may be engaged in monitoring the theme's entry. Notably, both the anticipation and receipt of themes were associated with pronounced activity in the frontal eye field, dorsolateral prefrontal cortex, posterior parietal cortex, dorsal caudate, and salience network. Overall, our results highlight that within a naturalistic music-listening context, the dynamic interplay between the frontoparietal, dopaminergic midbrain-striatal, and salience networks could allow for precise adjustments of control demands based on the cue-theme structure in unfamiliar songs.

Activation of neurons in the insular cortex and lateral hypothalamus during food anticipatory period caused by food restriction in mice

Mice fed a single meal daily at a fixed time display food anticipatory activity (FAA). It has been reported that the insular cortex (IC) plays an essential role in food anticipation, and lateral hypothalamus (LH) regulates the expression of FAA. However, how these areas contribute to FAA production is still unclear. Thus, we examined the temporal and spatial activation pattern of neurons in the IC and LH during the food anticipation period to determine their role in FAA establishment. We observed an increase of c-Fos-positive neurons in the IC and LH, including orexin neurons of male adult C57BL/6 mice. These neurons were gradually activated from the 1st day to 15th day of restricted feeding. The activation of these brain regions, however, peaked at a distinct point in the food restriction procedure. These results suggest that the IC and LH are differently involved in the neural network for FAA production.

Morphological study of neuropeptide Y expression in human and mouse anterior insular cortex: Overexpression in the insular cortex and nucleus accumbens in obese mice on a long-term obesogenic diet

BACKGROUND

The anterior lobe of the insular cortex (aINS) is a cortical region that has reciprocal connections with limbic centers such as the anterior cingulate cortex, prefrontal cortex, amygdala and nucleus accumbens (NAc). In fact, the aINS has been involved in the integration of autonomic information for emotional and motivational functions. The compulsive consumption of drugs or high-fat foods induces alterations at both behavioural and brain levels. Brain reward circuits are altered in response to continued intake, in particular the dopaminergic projections from the ventral tegmental area (VTA) to the NAc. The aINS has multiple connections with the components of this system. In recent years, efforts have been made to better understand the fundamental role of the aINS in addiction, making it one of the key centres of interest for research into new treatments for addiction.

OBJECTIVES

The present work focuses on studying 1.- whether the human aINS expresses orexigenic peptides such as neuropeptide Y (NPY), a peptide known to induce hyperphagia, and which has been implicated in the onset and development of obesity, 2.- the long-term effect of an obesogenic diet on NPY expression in the aINS and NAc of C57BL/6 mice.

METHODS

A total of 17 female C57BL/6 J mice were used in this study. Female mice were fed ad libitum with water and, either a standard diet (SD) or a high-fat diet (HFD) to induce obesity. There were seven female mice on the SD and ten on the HFD. The duration of the experiment was 180 days. We also studied 3 human adult brains (1 male and 2 females, mean age 55.7 ± 5.2 years). The morphological study was performed using immunohistochemistry and double immunofluorescence techniques to study the neurochemical profile of NPY neurons of the aINS and NAc of humans and mice.

RESULTS

Our morphological analysis demonstrates for the first time the basal expression of NPY in different layers of the human cortex (II, III, IV, V/VI), in a pattern similar to previous studies in other species. Furthermore, we observed an increase in the number of NPY-positive cells and their intracytoplasmic signal in the aINS and NAc of the obese mice subjected to a long-term obesogenic diet.

CONCLUSIONS

To our knowledge, this is the first study to show the distribution and expression of NPY in the human INS and how its expression is altered after prolonged treatment with an obesogenic diet in obese mice. Our findings may contribute to the understanding of the pathophysiological mechanisms underlying obesity in regions related to the reward system and associated with uncontrolled intake of high-fat foods, thus facilitating the identification of novel therapeutic targets.

Dissection of insular cortex layer 5 reveals two sublayers with opposing modulatory roles in appetitive drinking behavior

The insular cortex (insula) is known to play a modulatory role in feeding and drinking. Previous studies have revealed anterior-posterior differences of subcortical projections and roles for the insula, yet the anatomical and functional heterogeneity among the cortical layers remains poorly understood. Here, we show that layer 5 of the mouse dysgranular insula has two distinct neuronal subpopulations along the entire anterior-posterior axis: The L5a population, expressing NECAB1, projects bilaterally to the lateral and capsular divisions of the central amygdala, and the L5b population, expressing CTIP2, projects ipsilaterally to the parasubthalamic nucleus and the medial division of the central amygdala. Optogenetically activating L5a and L5b neuronal populations in thirsty male mice led to suppressed and facilitated water spout licking, respectively, without avoidance against or preference for the spout paired with the opto-stimulation. Our results suggest sublayer-specific bidirectional modulatory roles of insula layer 5 in the motivational aspect of appetitive behavior.

Adeno-associated virus 2 infection in children with non-A-E hepatitis

An outbreak of acute hepatitis of unknown aetiology in children was reported in Scotland1 in April 2022 and has now been identified in 35 countries2. Several recent studies have suggested an association with human adenovirus with this outbreak, a virus not commonly associated with hepatitis. Here we report a detailed case-control investigation and find an association between adeno-associated virus 2 (AAV2) infection and host genetics in disease susceptibility. Using next-generation sequencing, PCR with reverse transcription, serology and in situ hybridization, we detected recent infection with AAV2 in plasma and liver samples in 26 out of 32 (81%) cases of hepatitis compared with 5 out of 74 (7%) of samples from unaffected individuals. Furthermore, AAV2 was detected within ballooned hepatocytes alongside a prominent T cell infiltrate in liver biopsy samples. In keeping with a CD4+ T-cell-mediated immune pathology, the human leukocyte antigen (HLA) class II HLA-DRB1*04:01 allele was identified in 25 out of 27 cases (93%) compared with a background frequency of 10 out of 64 (16%; P = 5.49 × 10-12). In summary, we report an outbreak of acute paediatric hepatitis associated with AAV2 infection (most likely acquired as a co-infection with human adenovirus that is usually required as a 'helper virus' to support AAV2 replication) and disease susceptibility related to HLA class II status.

Mesolimbic dopamine release precedes actively sought aversive stimuli in mice

In some models, animals approach aversive stimuli more than those housed in an enriched environment. Here, we found that male mice in an impoverished and unstimulating (i.e., boring) chamber without toys sought aversive air puffs more often than those in an enriched chamber. Using this animal model, we identified the insular cortex as a regulator of aversion-seeking behavior. Activation and inhibition of the insular cortex increased and decreased the frequencies of air-puff self-stimulation, respectively, and the firing patterns of insular neuron ensembles predicted the self-stimulation timing. Dopamine levels in the ventrolateral striatum decreased with passive air puffs but increased with actively sought puffs. Around 20% of mice developed intense self-stimulation despite being offered toys, which was prevented by administering opioid receptor antagonists. This study establishes a basis for comprehending the neural underpinnings of usually avoided stimulus-seeking behaviors.

Cardiogenic control of affective behavioural state

Emotional states influence bodily physiology, as exemplified in the top-down process by which anxiety causes faster beating of the heart1-3. However, whether an increased heart rate might itself induce anxiety or fear responses is unclear3-8. Physiological theories of emotion, proposed over a century ago, have considered that in general, there could be an important and even dominant flow of information from the body to the brain9. Here, to formally test this idea, we developed a noninvasive optogenetic pacemaker for precise, cell-type-specific control of cardiac rhythms of up to 900 beats per minute in freely moving mice, enabled by a wearable micro-LED harness and the systemic viral delivery of a potent pump-like channelrhodopsin. We found that optically evoked tachycardia potently enhanced anxiety-like behaviour, but crucially only in risky contexts, indicating that both central (brain) and peripheral (body) processes may be involved in the development of emotional states. To identify potential mechanisms, we used whole-brain activity screening and electrophysiology to find brain regions that were activated by imposed cardiac rhythms. We identified the posterior insular cortex as a potential mediator of bottom-up cardiac interoceptive processing, and found that optogenetic inhibition of this brain region attenuated the anxiety-like behaviour that was induced by optical cardiac pacing. Together, these findings reveal that cells of both the body and the brain must be considered together to understand the origins of emotional or affective states. More broadly, our results define a generalizable approach for noninvasive, temporally precise functional investigations of joint organism-wide interactions among targeted cells during behaviour.

Physiological Needs: Sensations and Predictions in the Insular Cortex

Physiological needs create powerful motivations (e.g., thirst and hunger). Studies in humans and animal models have implicated the insular cortex in the neural regulation of physiological needs and need-driven behavior. We review prominent mechanistic models of how the insular cortex might achieve this regulation and present a conceptual and analytical framework for testing these models in healthy and pathological conditions.

Reward and inhibition in obesity and cigarette smoking: Neurobiological overlaps and clinical implications

Cigarette smoking and obesity are the leading causes of premature morbidity and mortality and increase the risk of all-cause mortality four-fold when comorbid. Individuals with these conditions demonstrate neurobiological and behavioral differences regarding how they respond to rewarding stimuli or engage in inhibitory control. This narrative review examines the role of reward and inhibition in cigarette smoking and obesity independently, as well as recent research demonstrating an effect of increased body mass index (BMI) on neurocognitive function in individuals who smoke. It is possible that chronic smoking and overeating of highly palatable food, contributing to obesity, dysregulates reward neurocircuitry, subsequently leading to hypofunction of brain networks associated with inhibitory control. These brain changes do not appear to be specific to food or nicotine and, as a result, can potentiate continued cross-use. Changes to reward and inhibitory function due to increased BMI may also make cessation more difficult for those comorbid for obesity and smoking.

Odor imagery but not perception drives risk for food cue reactivity and increased adiposity

Mental imagery has been proposed to play a critical role in the amplification of cravings. Here we tested whether olfactory imagery drives food cue reactivity strength to promote adiposity in 45 healthy individuals. We measured odor perception, odor imagery ability, and food cue reactivity using self-report, perceptual testing, and neuroimaging. Adiposity was assessed at baseline and one year later. Brain responses to real and imagined odors were analyzed with univariate and multivariate decoding methods to identify pattern-based olfactory codes. We found that the accuracy of decoding imagined, but not real, odor quality correlated with a perceptual measure of odor imagery ability and with greater adiposity changes. This latter relationship was mediated by cue-potentiated craving and intake. Collectively, these findings establish odor imagery ability as a risk factor for weight gain and more specifically as a mechanism by which exposure to food cues promotes craving and overeating.

Experience-dependent plasticity of gustatory insular cortex circuits and taste preferences

Early experience with food influences taste preference in adulthood. How gustatory experience influences development of taste preferences and refinement of cortical circuits has not been investigated. Here, we exposed weanling mice to an array of taste solutions and determined the effects on the preference for sweet in adulthood. We demonstrate an experience-dependent shift in sucrose preference persisting several weeks following the termination of exposure. A shift in sucrose palatability, altered neural responsiveness to sucrose, and inhibitory synaptic plasticity in the gustatory portion of the insular cortex (GC) were also induced. The modulation of sweet preference occurred within a restricted developmental window, but restoration of the capacity for inhibitory plasticity in adult GC reactivated the sensitivity of sucrose preference to taste experience. Our results establish a fundamental link between gustatory experience, sweet preference, inhibitory plasticity, and cortical circuit function and highlight the importance of early life nutrition in setting taste preferences.

Modulation of GABAB receptors in the insula bidirectionally affects associative memory of epilectic rats in both spatial and non-spatial operant tasks

Background

Stimulation of gamma-aminobutyric acid (GABA) activity through GABA receptor agonists is the basic mechanism of many anticonvulsant drugs. Nevertheless, many of these GABergic drugs have adverse cognitive effects. We previously found that GABAB receptors (GABA_BRs) in the insula regulate operant associative memory in healthy rats. The present study aimed at investigating the effects of GABA_BR modulation in the insula on operant associative memory in epileptic rats, along with the underlying mechanisms.

Methods

The lithium-pilocarpine model of temporal lobe epilepsy (TLE) was established in male Sprague-Dawley rats. A 22-gauge stainless-steel guide cannula was surgically implanted into the granular insula cortex of the epileptic rats. Baclofen (125 ng/μl, 1 μl), CGP35348 (12.5 μg/μl, 1 μl), or saline (1 μl) was slowly infused through the guide cannula. The Intellicage automated behavioral testing system was used to evaluate operant associative memory of the epileptic rats, including non-spatial operant tasks (basic nosepoke learning and skilled nosepoke learning) and spatial operant tasks (chamber position learning). The expression of the GABA_BR subunits GB1 and GB2 in the insula was examined by immunofluorescence and Western blotting.

Results

The Intellicage tests demonstrated that baclofen significantly impaired basic nosepoke learning, skilled nosepoke learning and chamber position learning of the epileptic rats, while CGP35348 boosted these functions. Immunofluorescence staining revealed that GB1 and GB2 were expressed in the insula of the epileptic rats, and Western blotting analysis showed that baclofen enhanced while CGP35348 inhibited the expression of these subunits.

Conclusion

GABA_BRs in the insula bidirectionally regulate both spatial and non-spatial operant associative memory of epileptic rats. Effects of GABA_BRs on cognition should be taken into account when evaluating new possible treatments for people with epilepsy.

Medial orbitofrontal neurotrophin systems integrate hippocampal input into outcome-specific value representations

In everyday life, we mentally represent possible consequences of our behaviors and integrate specific outcome values into existing knowledge to inform decisions. The medial orbitofrontal cortex (MO) is necessary to adapt behaviors when outcomes are not immediately available-when they and their values need to be envisioned. Nevertheless, neurobiological mechanisms remain unclear. We find that the neuroplasticity-associated neurotrophin receptor tropomyosin receptor kinase B (TrkB) is necessary for mice to integrate outcome-specific value information into choice behavior. This function appears attributable to memory updating (and not retrieval) and the stabilization of dendritic spines on excitatory MO neurons, which led us to investigate inputs to the MO. Ventral hippocampal (vHC)-to-MO projections appear conditionally necessary for value updating, involved in long-term aversion-based value memory updating. Furthermore, vHC-MO-mediated control of choice is TrkB dependent. Altogether, we reveal a vHC-MO connection by which specific value memories are updated, and we position TrkB within this functional circuit.

Time to learn: The role of the molecular circadian clock in learning and memory

The circadian system plays an important role in aligning biological processes with the external time of day. A range of physiological functions are governed by the circadian cycle, including memory processes, yet little is understood about how the clock interfaces with memory at a molecular level. The molecular circadian clock consists of four key genes/gene families, Period, Clock, Cryptochrome, and Bmal1, that rhythmically cycle in an ongoing transcription-translation negative feedback loop that maintains an approximately 24-hour cycle within cells of the brain and body. In addition to their roles in generating the circadian rhythm within the brain's master pacemaker (the suprachiasmatic nucleus), recent research has suggested that these clock genes may function locally within memory-relevant brain regions to modulate memory across the day/night cycle. This review will discuss how these clock genes function both within the brain's central clock and within memory-relevant brain regions to exert circadian control over memory processes. For each core clock gene, we describe the current research that demonstrates a potential role in memory and outline how these clock genes might interface with cascades known to support long-term memory formation. Together, the research suggests that clock genes function locally within satellite clocks across the brain to exert circadian control over long-term memory formation and possibly other biological processes. Understanding how clock genes might interface with local molecular cascades in the hippocampus and other brain regions is a critical step toward developing treatments for the myriad disorders marked by dysfunction of both the circadian system and cognitive processes.

An insula hierarchical network architecture for active interoceptive inference

In the brain, the insular cortex receives a vast amount of interoceptive information, ascending through deep brain structures, from multiple visceral organs. The unique hierarchical and modular architecture of the insula suggests specialization for processing interoceptive afferents. Yet, the biological significance of the insula's neuroanatomical architecture, in relation to deep brain structures, remains obscure. In this opinion piece, we propose the Insula Hierarchical Modular Adaptive Interoception Control (IMAC) model to suggest that insula modules (granular, dysgranular and agranular), forming parallel networks with the prefrontal cortex and striatum, are specialized to form higher order interoceptive representations. These interoceptive representations are recruited in a context-dependent manner to support habitual, model-based and exploratory control of visceral organs and physiological processes. We discuss how insula interoceptive representations may give rise to conscious feelings that best explain lower order deep brain interoceptive representations, and how the insula may serve to defend the body and mind against pathological depression.

Genetics and neurobiology of eating disorders

Eating disorders (anorexia nervosa, bulimia nervosa and binge-eating disorder) are a heterogeneous class of complex illnesses marked by weight and appetite dysregulation coupled with distinctive behavioral and psychological features. Our understanding of their genetics and neurobiology is evolving thanks to global cooperation on genome-wide association studies, neuroimaging, and animal models. Until now, however, these approaches have advanced the field in parallel, with inadequate cross-talk. This review covers overlapping advances in these key domains and encourages greater integration of hypotheses and findings to create a more unified science of eating disorders. We highlight ongoing and future work designed to identify implicated biological pathways that will inform staging models based on biology as well as targeted prevention and tailored intervention, and will galvanize interest in the development of pharmacologic agents that target the core biology of the illnesses, for which we currently have few effective pharmacotherapeutics.

Metastable dynamics of neural circuits and networks

Cortical neurons emit seemingly erratic trains of action potentials or "spikes," and neural network dynamics emerge from the coordinated spiking activity within neural circuits. These rich dynamics manifest themselves in a variety of patterns, which emerge spontaneously or in response to incoming activity produced by sensory inputs. In this Review, we focus on neural dynamics that is best understood as a sequence of repeated activations of a number of discrete hidden states. These transiently occupied states are termed "metastable" and have been linked to important sensory and cognitive functions. In the rodent gustatory cortex, for instance, metastable dynamics have been associated with stimulus coding, with states of expectation, and with decision making. In frontal, parietal, and motor areas of macaques, metastable activity has been related to behavioral performance, choice behavior, task difficulty, and attention. In this article, we review the experimental evidence for neural metastable dynamics together with theoretical approaches to the study of metastable activity in neural circuits. These approaches include (i) a theoretical framework based on non-equilibrium statistical physics for network dynamics; (ii) statistical approaches to extract information about metastable states from a variety of neural signals; and (iii) recent neural network approaches, informed by experimental results, to model the emergence of metastable dynamics. By discussing these topics, we aim to provide a cohesive view of how transitions between different states of activity may provide the neural underpinnings for essential functions such as perception, memory, expectation, or decision making, and more generally, how the study of metastable neural activity may advance our understanding of neural circuit function in health and disease.

An implicit priming intervention alters brain and behavioral responses to high-calorie foods: a randomized controlled study

BACKGROUND

Conditioned food cues (e.g., smell, sight) can affect intake of foods associated with those cues, regardless of homeostatic need. As such, altering automatic associations with food cues could support weight loss or maintenance efforts by affecting the salience of those cues and the effort required to resist consumption.

OBJECTIVES

This study investigated neuronal and behavioral effects of an implicit priming (IP) intervention, in which negatively valenced images were paired with high-calorie foods and positively valenced images with low-calorie foods. Priming images were presented immediately before food images, but below conscious perception (20 ms). We hypothesized that this evaluative conditioning approach could alter food cue responses by modifying affective associations.

METHODS

The final sample included 41 adults with BMI ≥25 kg/m2 (n = 22, active IP; n = 19, control IP). In control IP, food images were primed with neutral, scrambled images. Participants completed a visual food cue task during fMRI, both before and after IP. To determine the replicability of prior behavioral findings, food image ratings were completed before and after IP as a secondary outcome.

RESULTS

In a whole-brain analysis, reduced dorsolateral prefrontal cortex (dlPFC) response to high-calorie foods was observed after active compared with control IP (t = 4.93, P = 0.033). With a region of interest analysis, reduced response to high-calorie foods in active compared with control IP was also observed in the striatum (t = 2.40, P = 0.009) and insula (t = 2.38, P = 0.010). Active compared with control IP was associated with reduced high-calorie food ratings (F = 4.70, P = 0.038).

CONCLUSIONS

Reduced insula and striatum response to high-calorie foods after active compared with control IP suggests effectiveness of IP in altering food cue salience. Reduced dlPFC response to high-calorie foods after active compared with control IP may reflect fewer attentional resources being directed to those images and reduced engagement of inhibitory processes.This trial was registered at clinicaltrials.gov as NCT02347527.

A genetically defined insula-brainstem circuit selectively controls motivational vigor

The anterior insular cortex (aIC) plays a critical role in cognitive and motivational control of behavior, but the underlying neural mechanism remains elusive. Here, we show that aIC neurons expressing Fezf2 (aICFezf2), which are the pyramidal tract neurons, signal motivational vigor and invigorate need-seeking behavior through projections to the brainstem nucleus tractus solitarii (NTS). aICFezf2 neurons and their postsynaptic NTS neurons acquire anticipatory activity through learning, which encodes the perceived value and the vigor of actions to pursue homeostatic needs. Correspondingly, aIC → NTS circuit activity controls vigor, effort, and striatal dopamine release but only if the action is learned and the outcome is needed. Notably, aICFezf2 neurons do not represent taste or valence. Moreover, aIC → NTS activity neither drives reinforcement nor influences total consumption. These results pinpoint specific functions of aIC → NTS circuit for selectively controlling motivational vigor and suggest that motivation is subserved, in part, by aIC's top-down regulation of dopamine signaling.

Cellular activity in insular cortex across seconds to hours: Sensations and predictions of bodily states

Our wellness relies on continuous interactions between our brain and body: different organs relay their current state to the brain and are regulated, in turn, by descending visceromotor commands from our brain and by actions such as eating, drinking, thermotaxis, and predator escape. Human neuroimaging and theoretical studies suggest a key role for predictive processing by insular cortex in guiding these efforts to maintain bodily homeostasis. Here, we review recent studies recording and manipulating cellular activity in rodent insular cortex at timescales from seconds to hours. We argue that consideration of these findings in the context of predictive processing of future bodily states may reconcile several apparent discrepancies and offer a unifying, heuristic model for guiding future work.

Neural network modelling reveals changes in directional connectivity between cortical and hypothalamic regions with increased BMI

BACKGROUND/OBJECTIVES

Obesity has been ascribed to corticostriatal regions taking control over homeostatic areas. To test this assumption, we applied an effective connectivity approach to reveal the direction of information flow between brain regions and the valence of connections (excitatory versus inhibitory) as a function of increased BMI and homeostatic state.

SUBJECTS/METHODS

Forty-one participants (21 overweight/obese) underwent two resting-state fMRI scans: after overnight fasting (hunger) and following a standardised meal (satiety). We used spectral dynamic causal modelling to unravel hunger and increased BMI-related changes in directed connectivity between cortical, insular, striatal and hypothalamic regions.

RESULTS

During hunger, as compared to satiety, we found increased excitation of the ventromedial prefrontal cortex over the ventral striatum and hypothalamus, suggesting enhanced top-down modulation compensating energy depletion. Increased BMI was associated with increased excitation of the anterior insula over the hypothalamus across the hunger and satiety conditions. The interaction of hunger and increased BMI yielded decreased intra-cortical excitation from the dorso-lateral to the ventromedial prefrontal cortex.

CONCLUSIONS

Our findings suggest that excess weight and obesity is associated with persistent top-down excitation of the hypothalamus, regardless of homeostatic state, and hunger-related reductions of dorso-lateral to ventromedial prefrontal inputs. These findings are compatible with eating without hunger and reduced self-regulation views of obesity.

Better living through understanding the insula: Why subregions can make all the difference

Insula function is considered critical for many motivated behaviors, with proposed functions ranging from attention, behavioral control, emotional regulation, goal-directed and aversion-resistant responding. Further, the insula is implicated in many neuropsychiatric conditions including substance abuse. More recently, multiple insula subregions have been distinguished based on anatomy, connectivity, and functional contributions. Generally, posterior insula is thought to encode more somatosensory inputs, which integrate with limbic/emotional information in middle insula, that in turn integrate with cognitive processes in anterior insula. Together, these regions provide rapid interoceptive information about the current or predicted situation, facilitating autonomic recruitment and quick, flexible action. Here, we seek to create a robust foundation from which to understand potential subregion differences, and provide direction for future studies. We address subregion differences across humans and rodents, so that the latter's mechanistic interventions can best mesh with clinical relevance of human conditions. We first consider the insula's suggested roles in humans, then compare subregional studies, and finally describe rodent work. One primary goal is to encourage precision in describing insula subregions, since imprecision (e.g. including both posterior and anterior studies when describing insula work) does a disservice to a larger understanding of insula contributions. Additionally, we note that specific task details can greatly impact recruitment of various subregions, requiring care and nuance in design and interpretation of studies. Nonetheless, the central ethological importance of the insula makes continued research to uncover mechanistic, mood, and behavioral contributions of paramount importance and interest. This article is part of the special Issue on 'Neurocircuitry Modulating Drug and Alcohol Abuse'.

Chronic Distress in Male Mice Impairs Motivation Compromising Both Effort and Reward Processing With Altered Anterior Insular Cortex and Basolateral Amygdala Neural Activation

In humans and mammals, effort-based decision-making for monetary or food rewards paradigms contributes to the study of adaptive goal-directed behaviours acquired through reinforcement learning. Chronic distress modelled by repeated exposure to glucocorticoids in rodents induces suboptimal decision-making under uncertainty by impinging on instrumental acquisition and prompting negative valence behaviours. In order to further disentangle the motivational tenets of adaptive decision-making, this study addressed the consequences of enduring distress on relevant effort and reward-processing dimensions. Experimentally, appetitive and consummatory components of motivation were evaluated in adult C57BL/6JRj male mice experiencing chronic distress induced by oral corticosterone (CORT), using multiple complementary discrete behavioural tests. Behavioural data (from novelty suppressed feeding, operant effort-based choice, free feeding, and sucrose preference tasks) collectively show that behavioural initiation, effort allocation, and hedonic appreciation and valuation are altered in mice exposed to several weeks of oral CORT treatment. Additionally, data analysis from FosB immunohistochemical processing of postmortem brain samples highlights CORT-dependent dampening of neural activation in the anterior insular cortex (aIC) and basolateral amygdala (BLA), key telencephalic brain regions involved in appetitive and consummatory motivational processing. Combined, these results suggest that chronic distress-induced irregular aIC and BLA neural activations with reduced effort production and attenuated reward value processing during reinforcement-based instrumental learning could result in maladaptive decision-making under uncertainty. The current study further illustrates how effort and reward processing contribute to adjust the motivational threshold triggering goal-directed behaviours in versatile environments.

Chronic social defeat stress impairs goal-directed behavior through dysregulation of ventral hippocampal activity in male mice

Chronic stress is a risk factor for a variety of psychiatric disorders, including depression. Although impairments to motivated behavior are a major symptom of clinical depression, little is known about the circuit mechanisms through which stress impairs motivation. Furthermore, research in animal models for depression has focused on impairments to hedonic aspects of motivation, whereas patient studies suggest that impairments to appetitive, goal-directed motivation contribute significantly to motivational impairments in depression. Here, we characterized goal-directed motivation in repeated social defeat stress (R-SDS), a well-established mouse model for depression in male mice. R-SDS impaired the ability to sustain and complete goal-directed behavior in a food-seeking operant lever-press task. Furthermore, stress-exposed mice segregated into susceptible and resilient subpopulations. Interestingly, susceptibility to stress-induced motivational impairments was unrelated to stress-induced social withdrawal, another prominent effect of R-SDS in mouse models. Based on evidence that ventral hippocampus (vHP) modulates sustainment of goal-directed behavior, we monitored vHP activity during the task using fiber photometry. Successful task completion was associated with suppression of ventral hippocampal neural activity. This suppression was diminished after R-SDS in stress-susceptible but not stress-resilient mice. The serotonin selective reuptake inhibitor (SSRI) escitalopram and ketamine both normalized vHP activity during the task and restored motivated behavior. Furthermore, optogenetic vHP inhibition was sufficient to restore motivated behavior after stress. These results identify vHP hyperactivity as a circuit mechanism of stress-induced impairments to goal-directed behavior and a putative biomarker that is sensitive to antidepressant treatments and that differentiates susceptible and resilient individuals.

Top-down control of conditioned overconsumption is mediated by insular cortex Nos1 neurons

Associative learning allows animals to adapt their behavior in response to environmental cues. For example, sensory cues associated with food availability can trigger overconsumption even in sated animals. However, the neural mechanisms mediating cue-driven non-homeostatic feeding are poorly understood. To study this, we recently developed a behavioral task in which contextual cues increase feeding even in sated mice. Here, we show that an insular cortex to central amygdala circuit is necessary for conditioned overconsumption, but not for homeostatic feeding. This projection is marked by a population of glutamatergic nitric oxide synthase-1 (Nos1)-expressing neurons, which are specifically active during feeding bouts. Finally, we show that activation of insular cortex Nos1 neurons suppresses satiety signals in the central amygdala. The data, thus, indicate that the insular cortex provides top-down control of homeostatic circuits to promote overconsumption in response to learned cues.

The insulo-opercular cortex encodes food-specific content under controlled and naturalistic conditions

The insulo-opercular network functions critically not only in encoding taste, but also in guiding behavior based on anticipated food availability. However, there remains no direct measurement of insulo-opercular activity when humans anticipate taste. Here, we collect direct, intracranial recordings during a food task that elicits anticipatory and consummatory taste responses, and during ad libitum consumption of meals. While cue-specific high-frequency broadband (70–170 Hz) activity predominant in the left posterior insula is selective for taste-neutral cues, sparse cue-specific regions in the anterior insula are selective for palatable cues. Latency analysis reveals this insular activity is preceded by non-discriminatory activity in the frontal operculum. During ad libitum meal consumption, time-locked high-frequency broadband activity at the time of food intake discriminates food types and is associated with cue-specific activity during the task. These findings reveal spatiotemporally-specific activity in the human insulo-opercular cortex that underlies anticipatory evaluation of food across both controlled and naturalistic settings.

Animal studies have shown that insulo-opercular network function is critical in gustation and in behaviour based on anticipated food availability. The authors describe activities within the human insulo-opercular cortex which underlie anticipatory food evaluation in both controlled and naturalistic settings.

Prior Cocaine Exposure Increases Firing to Immediate Reward While Attenuating Cue and Context Signals Related to Reward Value in the Insula

The insula contributes to behavioral control and is disrupted by substance abuse, yet we know little about the neural signals underlying these functions or how they are disrupted after chronic drug self-administration. Here, male and female rats self-administered either cocaine (experimental group) or sucrose (control) for 12 consecutive days. After a 1 month withdrawal period, we recorded from insula while rats performed a previously learned reward-guided decision-making task. Cocaine-exposed rats were more sensitive to value manipulations and were faster to respond. These behavioral changes were accompanied by elevated counts of neurons in the insula that increased firing to reward. These neurons also fired more strongly at the start of long-delay trials, when a more immediate reward would be expected, and fired less strongly in anticipation of the actual delivery of delayed rewards. Although reward-related firing to immediate reward was enhanced after cocaine self-administration, reward-predicting cue and context signals were attenuated. In addition to revealing novel firing patterns unique to insula, our data suggest changes in such neural activity likely contribute to impaired decision making observed after drug use.SIGNIFICANCE STATEMENT The insula plays a clear role in drug addiction and drug-induced impairments of decision making, yet there is little understanding of its underlying neural signals. We found that chronic cocaine self-administration reduces cue and context encoding in insula while enhancing signals related to immediate reward. These changes in neural activity likely contribute to impaired decision making and impulsivity observed after drug use.

Rethinking the role of taste processing in insular cortex and forebrain circuits

Over the years, many approaches towards studying the taste-responsive area of insular cortex have focused on how basic taste information is represented, and how lesions or silencing of this area impact taste-focused behaviors. Here, we review and highlight recent studies that imply that insular cortex does not contain a "primary" taste cortex in the traditional sense. Rather, taste is employed in concert with other internal and external sensory modalities by highly interconnected regions of insular cortex to guide ingestive decision-making, especially in context of estimating risk and reward. In rodent models, this may best be seen in context of foraging behaviors, which require flexibility and are dependent on learning and memory processes.

Optogenetic Activation of Dopamine Receptor D1 and D2 Neurons in Anterior Cingulate Cortex Differentially Modulates Trigeminal Neuropathic Pain

Background:

Anterior cingulate cortex (ACC) is a critical brain center for chronic pain processing. Dopamine signaling in the brain has been demonstrated to contribute to descending pain modulation. However, the role of ACC dopamine receptors in chronic neuropathic pain remains unclear.

Objective:

In this study, we investigated the effect of optogenetic activation of ACC dopamine receptors D1- and D2-expressing neurons on trigeminal neuropathic pain.

Methods:

Chronic constriction injury of infraorbital nerve (CCI-ION) was carried out to induce trigeminal neuropathic pain in mice. We conducted optogenetic stimulation to specifically activate D1- and D2-expressing neurons in the ACC. Western blotting and immunofluorescence staining were used to examine ACC D1 and D2 expression and localization. The von Frey and real-time place preference tests were performed to measure evoked mechanical pain and nonreflexive emotional pain behaviors, respectively.

Results:

We observed that dopamine receptors D1 and D2 in the ACC are primarily expressed in excitatory neurons and that the D2 receptor is differentially regulated in the early and late phases of trigeminal neuropathic pain. Optogenetic activation of D1-expressing neurons in the ACC markedly exacerbates CCI-ION-induced trigeminal neuropathic pain in both early and late phases, but optogenetic activation of D2-expressing neurons in the ACC robustly ameliorates such pain in its late phase.

Conclusion:

Our results suggest that dopamine receptors D1 and D2 in the ACC play different roles in the modulation of trigeminal neuropathic pain.

Transient Delay-Period Activity of Agranular Insular Cortex Controls Working Memory Maintenance in Learning Novel Tasks

Whether transient or sustained neuronal activity during the delay period underlies working memory (WM) has been debated. Here, we report that transient, but not sustained, delay-period activity in mouse anterior agranular insular cortex (aAIC) plays a dominant role in maintaining WM information during learning of novel olfactory tasks. By optogenetic screening over 12 brain regions, we found that suppressing aAIC activity markedly impaired olfactory WM maintenance during learning. Single-unit recording showed that odor-selective aAIC neurons with predominantly transient firing patterns encoded WM information. Both WM task performance and transient-neuron proportion were enhanced and reduced by activating and suppressing the delay-period activity of the projection from medial prefrontal cortex (mPFC) to aAIC. The ability of mice to resist delay-period distractors also correlated with an increased percentage of transient neurons. Therefore, transient, but not sustained, aAIC neuronal activity during the delay period is largely responsible for maintaining information while learning novel WM tasks.

Cortical processing of chemosensory and hedonic features of taste in active licking mice

In the last two decades, a considerable amount of work has been devoted to investigating the neural processing and dynamics of the primary taste cortex of rats. Surprisingly, much less information is available on cortical taste electrophysiology in awake mice, an animal model that is taking on a more prominent role in taste research. Here we present electrophysiological evidence demonstrating how the gustatory cortex (GC) encodes the basic taste qualities (sweet, salty, sour, and bitter) and water when stimuli are actively sampled through licking, the stereotyped behavior by which mice control the access of fluids in the mouth. Mice were trained to receive each stimulus on a fixed ratio schedule in which they had to lick a dry spout six times to receive a tastant on the seventh lick. Electrophysiological recordings confirmed that GC neurons encode both chemosensory and hedonic aspects of actively sampled tastants. In addition, our data revealed two other main findings: GC neurons rapidly encode information about taste qualities in as little as 120 ms, and nearly half of the recorded neurons exhibit spiking activity entrained to licking at rates up to 8 Hz. Overall, our results highlight how the GC of active licking mice rapidly encodes information about taste qualities as well as ongoing sampling behavior, expanding our knowledge on cortical taste processing.NEW & NOTEWORTHY Relatively little information is available on the neural dynamics of taste processing in the mouse gustatory cortex (GC). In this study we investigate how the GC encodes chemosensory and palatability features of a wide panel of gustatory stimuli when actively sampled through licking. Our results show that GC neurons broadly encode basic taste qualities but also process taste hedonics and licking information in a temporally dynamic manner.

Dynamic Representation of Taste-Related Decisions in the Gustatory Insular Cortex of Mice

Research over the past decade has established the gustatory insular cortex (GC) as a model for studying howprimary sensory cortices integrate sensory,affective, and cognitive signals. This integration occurs through time-varyingpatterns of neural activity. Selective silencing of GC activity during specific temporal windows provided evidence forGC’s role in mediating taste palatability and expectation. Recent results also suggest that this areamay play a role in decision making. However, existing data are limited to GC involvement in controlling the timing of stereotyped, orofacial reactions to aversive tastants during consumption. Here,we present electrophysiological, chemogenetic, and optogenetic results demonstrating the key role of GCin the executionof a taste-guided, reward-directed decision-making task. Mice were trained in a two-alternative choice task, in which they had to associate tastants sampled from a central spout with different actions (i.e., licking either a left or a right spout). Stimulus sampling and action were separated by a delay period. Electrophysiological recordings revealed chemosensory processing during the sampling period and the emergence of task-related, cognitive signals during the delay period. Chemogenetic silencing of GCimpaired task performance. Optogenetic silencing of GC allowed us to tease apart the contribution of activity during sampling and delay periods. Although silencing during the sampling period had no effect, silencing during the delay period significantly impacted behavioral performance, demonstrating the importance of the cognitive signals processed by GC in driving decision making. Altogether, our data highlight a novel role ofGCin controlling taste-guided, reward-directed choices and actions.

Relying on behavioral electrophysiology and neural manipulations, Vincis, Chen, et al. demonstrate that neurons in the gustatory cortex (GC) encode perceptual and cognitive signals important for tasteguided choices. These data demonstrate a novel role of GC as a key area for sensorimotor transformations related to gustatory perceptual decision making.

Estimation of Current and Future Physiological States in Insular Cortex

Interoception, the sense of internal bodily signals, is essential for physiological homeostasis, cognition, and emotions. While human insular cortex (InsCtx) is implicated in interoception, the cellular and circuit mechanisms remain unclear. We imaged mouse InsCtx neurons during two physiological deficiency states: hunger and thirst. InsCtx ongoing activity patterns reliably tracked the gradual return to homeostasis but not changes in behavior. Accordingly, while artificial induction of hunger or thirst in sated mice via activation of specific hypothalamic neurons (AgRP or SFOGLUT) restored cue-evoked food- or water-seeking, InsCtx ongoing activity continued to reflect physiological satiety. During natural hunger or thirst, food or water cues rapidly and transiently shifted InsCtx population activity to the future satiety-related pattern. During artificial hunger or thirst, food or water cues further shifted activity beyond the current satiety-related pattern. Together with circuit-mapping experiments, these findings suggest that InsCtx integrates visceral-sensory signals of current physiological state with hypothalamus-gated amygdala inputs that signal upcoming ingestion of food or water to compute a prediction of future physiological state.

Control of non-homeostatic feeding in sated mice using associative learning of contextual food cues

Feeding is a complex motivated behavior controlled by a distributed neural network that processes sensory information to generate adaptive behavioral responses. Accordingly, studies using appetitive Pavlovian conditioning confirm that environmental cues that are associated with food availability can induce feeding even in satiated subjects. However, in mice, appetitive conditioning generally requires intensive training and thus can impede molecular studies that often require large numbers of animals. To address this, we developed and validated a simple and rapid context-induced feeding (Ctx-IF) task in which cues associated with food availability can later lead to increased food consumption in sated mice. We show that the associated increase in food consumption is driven by both positive and negative reinforcement and that spaced training is more effective than massed training. Ctx-IF can be completed in ~1 week and provides an opportunity to study the molecular mechanisms and circuitry underlying non-homeostatic eating. We have used this paradigm to map brain regions that are activated during Ctx-IF with cFos immunohistochemistry and found that the insular cortex, and other regions, are activated following exposure to cues denoting the availability of food. Finally, we show that inhibition of the insular cortex using GABA agonists impairs performance of the task. Our findings provide a novel assay in mice for defining the functional neuroanatomy of appetitive conditioning and identify specific brain regions that are activated during the development of learned behaviors that impact food consumption.

Dimensional anhedonia and the adolescent brain: reward and aversion anticipation, effort and consummation

BACKGROUND

Given the heterogeneity of depression the Research Domain Criteria Framework suggests a dimensional approach to understanding the nature of mental illness. Neural reward function has been suggested as underpinning the symptom of anhedonia in depression but how anhedonia is related to aversion processing is unclear.

AIMS

To assess how the dimensional experience of anhedonia and depression severity relate to reward and aversion processing in the human brain.

METHOD

We examined adolescents and emerging adults (n = 84) in the age range 13-21 years. Using a dimensional approach we examined how anhedonia and depression related to physical effort to gain reward or avoid aversion and neural activity during the anticipation, motivation/effort and consummation of reward and aversion.

RESULTS

As anhedonia increased physical effort to gain reward decreased. As anhedonia increased neural activity decreased during effort to avoid in the precuneus and insula (trend) and increased in the caudate during aversive consummation. We found participants with depression symptoms invested less physical effort than controls and had blunted neural anticipation of reward and aversion in the precuneus, insula and prefrontal cortex and blunted neural activity during effort for reward in the putamen.

CONCLUSIONS

We show for the first time that both physical effort and neural activity during effort correlate with anhedonia in adolescents and that amotivation might be a specific deficit of anhedonia irrespective of valence. Future work will assess if these neural mechanisms can be used to predict blunted approach and avoidance in adolescents at risk of depression.

A neural network for information seeking

Humans and other animals often show a strong desire to know the uncertain rewards their future has in store, even when they cannot use this information to influence the outcome. However, it is unknown how the brain predicts opportunities to gain information and motivates this information-seeking behavior. Here we show that neurons in a network of interconnected subregions of primate anterior cingulate cortex and basal ganglia predict the moment of gaining information about uncertain rewards. Spontaneous increases in their information prediction signals are followed by gaze shifts toward objects associated with resolving uncertainty, and pharmacologically disrupting this network reduces the motivation to seek information. These findings demonstrate a cortico-basal ganglia mechanism responsible for motivating actions to resolve uncertainty by seeking knowledge about the future.

Animals resolve uncertainty by seeking knowledge about the future. How the brain controls this is unclear. The authors show that a network including primate anterior cingulate cortex and basal ganglia encodes opportunities to gain information about uncertain rewards and mediates information seeking.