Autonomic arousal in an appetitive context in primates: a behavioural and neural analysis

Quantifying animals' perception of environmental predictability using anticipatory behavior

Animals under human care often experience predictable daily husbandry events, which can promote the development of anticipatory behavior. Previous research suggests even short delays in the arrival of a predictable, desired outcome can lead to negative welfare outcomes for animals. As such, providing reliable information to animals regarding the onset of important events may be a simple but useful method to support positive welfare. Here we evaluated the quantitative characteristics of anticipatory behavior of a California sea lion at the San Francisco Zoo in three situations (1) when the animal had accurate information about the occurrence of the event (temporally predictable training sessions), (2) when the information was semi-reliable (unscheduled training session), and (3) when a reliable signal was offered before unscheduled sessions. Results showed that providing a reliable cue resulted in a stronger temporal correlation of anticipation before the beginning of the unscheduled session, similar to the temporally predictable training session. However, providing a reliable cue did not reduce the intensity of the anticipatory behavior. We propose to take into account two aspects of the quantitative characteristics of anticipatory behavior: correlation with time until a desired event (correlation) and intensity, where the correlation indicates the ability of an individual animal to predict the occurrence of an event, and the intensity indicates the degree of sensitivity of the animal to reward. We discuss the implications for animal welfare and husbandry.

Induction of Anxiety-Like Phenotypes by Knockdown of Cannabinoid Type-1 Receptors in the Amygdala of Marmosets

The amygdala is an important hub for regulating emotions and is involved in the pathophysiology of many mental diseases, such as depression and anxiety. Meanwhile, the endocannabinoid system plays a crucial role in regulating emotions and mainly functions through the cannabinoid type-1 receptor (CB1R), which is strongly expressed in the amygdala of non-human primates (NHPs). However, it remains largely unknown how the CB1Rs in the amygdala of NHPs regulate mental diseases. Here, we investigated the role of CB1R by knocking down the cannabinoid receptor 1 (CNR1) gene encoding CB1R in the amygdala of adult marmosets through regional delivery of AAV-SaCas9-gRNA. We found that CB1R knockdown in the amygdala induced anxiety-like behaviors, including disrupted night sleep, agitated psychomotor activity in new environments, and reduced social desire. Moreover, marmosets with CB1R-knockdown had up-regulated plasma cortisol levels. These results indicate that the knockdown of CB1Rs in the amygdala induces anxiety-like behaviors in marmosets, and this may be the mechanism underlying the regulation of anxiety by CB1Rs in the amygdala of NHPs.

Obesity-mediated Lipoinflammation Modulates Food Reward Responses

Accumulation of white adipose tissue (WAT) during obesity is associated with the development of chronic low-grade inflammation, a biological process known as lipoinflammation. Systemic and central lipoinflammation accumulates pro-inflammatory cytokines including IL-6, IL-1β and TNF-α in plasma and also in brain, disrupting neurometabolism and cognitive behavior. Obesity-mediated lipoinflammation has been reported in brain regions of the mesocorticolimbic reward circuit leading to alterations in the perception and consumption of ultra-processed foods. While still under investigation, lipoinflammation targets two major outcomes of the mesocorticolimbic circuit during food reward: perception and motivation ("Wanting") and the pleasurable feeling of feeding ("Liking"). This review will provide experimental and clinical evidence supporting the contribution of obesity- or overnutrition-related lipoinflammation affecting the mesocorticolimbic reward circuit and enhancing food reward responses. We will also address neuroanatomical targets of inflammatory profiles that modulate food reward responses during obesity and describe potential cellular and molecular mechanisms of overnutrition linked to addiction-like behavior favored by brain lipoinflammation.

Of ugly gains and happy losses: An event-related potential study of interactions of the intrinsic and acquired valence of emotional pictures

During the last decades, event-related potential research on the processing of intrinsic and acquired valence has made great progress, but the two dimensions rarely varied simultaneously. Only that way, however, can we investigate whether the acquisition of extrinsic valence varies with intrinsic valence and whether intrinsic and acquired valence share the same brain mechanisms. Forty-five participants performed associative learning of gains and losses, using pictures varying on intrinsic valence (positive, negative) and outcome (90 % gain, 50 %/50 %, 90 % loss). 64-channel EEG was recorded. During acquisition, one picture from each valence/outcome combination was repeatedly presented, followed by abstract outcome information (+10 ct, -10 ct) at the predefined probability. In the test phase, participants pressed buttons to earn the real gains and avoid the real losses associated with the pictures. Here, effects of outcome and/or its congruence with intrinsic valence were observed for RT, error rate, frontal theta power, posterior P2, P300, and LPP. Moreover, outcome systematically affected post-test valence and arousal ratings. During acquisition, a contingency effect (90 % > 50 %) on amplitude of a frontal negative slow wave accompanied the progress of learning, independently of outcome, valence, and congruence. The relative absence of outcome effects during acquisition suggests "cold" semantic rather than genuinely affective processing of gains and losses. However, with real gains and losses in the test phase, "hot" affective processing took place, and outcome and its congruence with intrinsic valence influenced behavior and neural processing. Finally, the data suggest both shared and distinct brain mechanisms of intrinsic and acquired valence.

Peripherally-administered amphetamine induces plasticity in medial prefrontal cortex and nucleus accumbens in rats with amygdala lesions: implications for neural models of memory modulation

The amygdala has been implicated in a variety of functions linked to emotions. One popular view is that the amygdala modulates consolidation in other brain systems thought to be mainly involved in learning and memory processes. This series of experiments represents a further exploration into the role of the amygdala in memory modulation and consolidation. One interesting line of research has shown that drugs of abuse, like amphetamine, produce dendritic changes in select brain regions and these changes are thought to be equivalent to a usurping of normal plasticity processes. We were interested in the possibility that this modulation of plasticity processes would be dependent on interactions with the amygdala. According to the modulation view of amygdala function, amphetamine would activate modulation mechanisms in the amygdala that would alter plasticity processes in other brain regions. If the amygdala was rendered dysfunctional, these effects should not occur. Accordingly, this series of experiments evaluated the effects of extensive neurotoxic amygdala damage on amphetamine-induced dendritic changes in the nucleus accumbens and prefrontal cortex. The results showed that rats with large lesions of the amygdala showed the normal pattern of dendritic changes in these brain regions. This pattern of results suggests that the action of not all memory modulators, activated during emotional events, require the amygdala to impact memory.

Space, time, and context drive anticipatory behavior: Considerations for understanding the behavior of animals in human care

Animal-based measures reflecting the welfare state of individuals are critical for ensuring the well-being of animals under human care. Anticipatory behavior is one potential animal-based measure that has gained traction in recent years, as it is theorized to relate to animals' reward sensitivity. It is of particular interest as an assessment for animals living under human care, as the predictability of the captive environment lends itself to the development of this class of behaviors. Animals are likely to exhibit anticipation in locations related to the anticipated event, often in temporally predictable time frames, and before specific contexts they experience in their day-to-day management. In this sense and under certain circumstances, anticipatory behaviors are likely to drive observed behavioral or space use patterns of animals under human care. Drawing conclusions from such data without identifying anticipation may result in misleading conclusions. Here we discuss how space, time, and context are related to patterns of anticipatory behaviors in animals under human care, how unidentified anticipation may alter conclusions regarding animal behavior or welfare under certain circumstances.

Conditional Regulation of Blood Pressure in Response to Emotional Stimuli by the Central Nucleus of the Amygdala in Rats

Humans and animals can determine whether a situation is favorable to them and act accordingly. For this, the autonomic tuning of the cardiovascular system to supply energy to active skeletal muscles through the circulatory system is as important as motor control. However, how the autonomic cardiovascular responses are regulated in dynamically changing environments and the neuronal mechanisms underlying these responses remain unclear. To resolve these issues, we recorded the blood pressure and heart rate of head-restrained rats during dynamically changing appetitive and aversive classical conditioning tasks. The rats displayed various associations between conditioned stimuli and unconditioned stimuli in appetitive (sucrose water), neutral (no outcome), and aversive (air puff) blocks. The blood pressure and heart rate in the appetitive block gradually increased in response to the reward-predicting cue and the response to the actual reward vigorously increased. The reward-predictive response was significantly higher than the responses obtained in the neutral and aversive condition blocks. To investigate whether the reward-predictive pressor response was caused by orofacial movements such as anticipatory licking behavior, we separately analyzed high- and low-licking trials. The conditioned pressor response was observed even in trials with low-licking behaviors. Blood pressure and heart rate responses to the air puff-predicting cue in the aversive block were not significantly different from the responses in the neutral block. The conditioned blood pressure response rapidly changed with condition block switching. Furthermore, to examine the contribution of the amygdala as an emotion center to these conditioned responses, we bilaterally microinjected a GABA_A receptor agonist, muscimol, into the central nucleus of the amygdala. Pharmacological inactivation of the central nucleus of the amygdala significantly decreased the reward-predictive pressor responses. These results suggest that the blood pressure is adaptively and rapidly regulated by emotional conditioned stimuli and that the central nucleus of the amygdala participates in regulating the pressor response in dynamically changing situations.

Differential Effects of the Inactivation of Anterior and Posterior Orbitofrontal Cortex on Affective Responses to Proximal and Distal Threat, and Reward Anticipation in the Common Marmoset

Structural and functional abnormalities of the orbitofrontal cortex (OFC) have been implicated in affective disorders that manifest anxiety-related symptoms. However, research into the functions of primate OFC has predominantly focused on reward-oriented rather than threat-oriented responses. To redress this imbalance, the present study performed a comprehensive analysis of the independent role of 2 distinct subregions of the central OFC (anterior area 11; aOFC and posterior area 13; pOFC) in the processing of distal and proximal threat. Temporary inactivation of both aOFC and pOFC heightened responses to distal threat in the form of an unknown human, but not to proximal threat assessed in a discriminative Pavlovian conditioning task. Inactivation of the aOFC, however, did unexpectedly blunt conditioned threat responses, although the effect was not valence-specific, as conditioned appetitive responses were similarly blunted and appeared restricted to a discriminative version of the task (when both CS⁻ and CS⁺ are present within a session). Inactivation of the pOFC did not affect conditioned responses to either proximal threat or reward and basal cardiovascular activity was unaffected by manipulations of activity in either subregion. The results highlight the contribution of aOFC and pOFC to regulation of responses to more distal uncertain but not proximal, certain threat and reveal their opposing contribution to that of the immediately adjacent medial OFC, area 14.

Differential Contribution of Anterior and Posterior Midcingulate Subregions to Distal and Proximal Threat Reactivity in Marmosets

The midcingulate cortex (MCC) is associated with cognition and emotion regulation. Structural and correlational functional evidence suggests that rather than being homogenous, the MCC may have dissociable functions that can be mapped onto distinct subregions. In this study, we use the marmoset monkey to causally investigate the contributions of two proposed subregions of the MCC: the anterior and posterior midcingulate cortices (aMCC and pMCC) to behavioral and cardiovascular correlates of threat processing relevant to anxiety disorders. Transient inactivation of the aMCC decreased anxiety-like responses to a postencounter distal threat, namely an unfamiliar human intruder, while inactivation of the pMCC showed a mild but opposing effect. Furthermore, although inactivation of neither MCC subregions had any effect on basal cardiovascular activity, aMCC inactivation blunted the expression of both cardiovascular and behavioral conditioned responses to a predictable proximal threat (a rubber snake) during the extinction in a Pavlovian conditioning task, with pMCC inactivation having again an opposing effect, but primarily on the behavioral response. These findings suggest that the MCC is indeed functionally heterogeneous with regards to its role in threat processing, with aMCC providing a marked facilitative contribution to the expression of the emotional response to both proximal and distal threat.

Cardiac response in aversive and appetitive olfactory conditioning: Evidence for a valence-independent CS-elicited bradycardia

While the examination of conditioned cardiac responses is well established in human fear conditioning research, comparable studies using less-aversive or rather appetitive unconditioned stimuli (UCS) are sparse and results are mixed. Therefore, the aim of this study was a systematic analysis of cardiac reactions in aversive and appetitive conditioning. Olfactory stimuli were used as unconditioned stimuli as they are suitable reinforcers in both an aversive and an appetitive conditioning offering the opportunity for a comparison between conditioned responses. In total, n = 86 participants took part in both an aversive and an appetitive differential conditioning task with a counterbalanced order across participants. Aversive or appetitive odors, respectively, served as UCS and neutral geometrical figures as CS. Subjective ratings, skin conductance response (SCRs), and evoked cardiac reactions were analyzed and compared between tasks. Conditioned responses in subjective ratings could be observed in both aversive conditioning and appetitive conditioning, while SCRs discriminated between CS+ and CS- in aversive conditioning only. Regarding conditioned cardiac responses, the deceleration for the CS+ was longer than for the CS- in both tasks. In addition, a higher deceleration magnitude and a shorter acceleration for the CS+ as compared to the CS- were found in aversive but not in appetitive conditioning. There were medium-size correlations between aversive and appetitive CRs for subjective ratings and none for physiological responses. The results suggest similarities between cardiac response patterns in aversive and appetitive conditioning, which implies that bradycardia in conditioning might not be fear-specific but presents a valence-independent CS-elicited bradycardia.

Quantifying anhedonia-like symptoms in marmosets using appetitive Pavlovian conditioning

Blunted reward responsivity is associated with anhedonia in humans and is a core feature of depression. This protocol describes how to train the common marmoset, Callithrix jacchus, on an appetitive Pavlovian conditioning paradigm to measure behavioral and cardiovascular correlates of anticipatory and consummatory phases of reward processing. We describe how to use intracerebral infusions to manipulate brain regions whose activity is relevant to impaired reward processing in depression and how the paradigm can be used to test antidepressant efficacy. For complete details on the use and execution of this protocol, please refer to Alexander et al. (2019).

Development of a Classical Conditioning Task for Humans Examining Phasic Heart Rate Responses to Signaled Appetitive Stimuli: A Pilot Study

Cardiac responses to appetitive stimuli have been studied as indices of motivational states and attentional processes, the former being associated with cardiac acceleration and latter deceleration. Very few studies have examined heart rate changes in appetitive classical conditioning in humans. The current study describes the development and pilot testing of a classical conditioning task to assess cardiac responses to appetitive stimuli and cues that reliably precede them. Data from 18 adults were examined. They were shown initially neutral visual stimuli (putative CS) on a computer screen followed by pictures of high-caloric food (US). Phasic cardiac deceleration to food images was observed, consistent with an orienting response to motivationally significant stimuli. Similar responses were observed to non-appetitive stimuli when they were preceded by the cue associated with the food images, suggesting that attentional processes were engaged by conditioned stimuli. These autonomic changes provide significant information about classical conditioning effects in humans.

Efferent projections of CGRP/Calca-expressing parabrachial neurons in mice

The parabrachial nucleus (PB) is composed of glutamatergic neurons at the midbrain-hindbrain junction. These neurons form many subpopulations, one of which expresses Calca, which encodes the neuropeptide calcitonin gene-related peptide (CGRP). This Calca-expressing subpopulation has been implicated in a variety of homeostatic functions, but the overall distribution of Calca-expressing neurons in this region remains unclear. Also, while previous studies in rats and mice have identified output projections from CGRP-immunoreactive or Calca-expressing neurons, we lack a comprehensive understanding of their efferent projections. We began by identifying neurons with Calca mRNA and CGRP immunoreactivity in and around the PB, including populations in the locus coeruleus and motor trigeminal nucleus. Calca-expressing neurons in the PB prominently express the mu opioid receptor (Oprm1) and are distinct from neighboring neurons that express Foxp2 and Pdyn. Next, we used Cre-dependent anterograde tracing with synaptophysin-mCherry to map the efferent projections of these neurons. Calca-expressing PB neurons heavily target subregions of the amygdala, bed nucleus of the stria terminalis, basal forebrain, thalamic intralaminar and ventral posterior parvicellular nuclei, and hindbrain, in different patterns depending on the injection site location within the PB region. Retrograde axonal tracing revealed that the previously unreported hindbrain projections arise from a rostral-ventral subset of CGRP/Calca neurons. Finally, we show that these efferent projections of Calca-expressing neurons are distinct from those of neighboring PB neurons that express Pdyn. This information provides a detailed neuroanatomical framework for interpreting experimental work involving CGRP/Calca-expressing neurons and opioid action in the PB region.

Effects of Amygdala Lesions on Object-Based Versus Action-Based Learning in Macaques

The neural systems that underlie reinforcement learning (RL) allow animals to adapt to changes in their environment. In the present study, we examined the hypothesis that the amygdala would have a preferential role in learning the values of visual objects. We compared a group of monkeys (Macaca mulatta) with amygdala lesions to a group of unoperated controls on a two-armed bandit reversal learning task. The task had two conditions. In the What condition, the animals had to learn to select a visual object, independent of its location. And in the Where condition, the animals had to learn to saccade to a location, independent of the object at the location. In both conditions choice-outcome mappings reversed in the middle of the block. We found that monkeys with amygdala lesions had learning deficits in both conditions. Monkeys with amygdala lesions did not have deficits in learning to reverse choice-outcome mappings. Rather, amygdala lesions caused the monkeys to become overly sensitive to negative feedback which impaired their ability to consistently select the more highly valued action or object. These results imply that the amygdala is generally necessary for RL.

Inexpensive Home Infrared Living/Environment Sensor with Regional Thermal Information for Infant Physical and Psychological Development

The use of home-based image sensors for biological and environmental monitoring provides novel insight into health and development but it is difficult to evaluate people during their normal activities in their home. Therefore, we developed a low-cost infrared (IR) technology-based motion, location, temperature and thermal environment detection system that can be used non-invasively for long-term studies in the home environment. We tested this technology along with the associated analysis algorithm to visualize the effects of parental care and thermal environment on developmental state change in a non-human primate model, the common marmoset (Callithrix jacchus). To validate this system, we first compared it to a manual analysis technique and we then assessed the development of circadian rhythms in common marmosets from postnatal day 15–45. The semi-automatically tracked biological indices of locomotion velocity (BV) and body surface temperature (BT) and the potential psychological index of place preference toward the door (BD), showed age-dependent shifts in circadian phase patterns. Although environmental variables appeared to affect circadian rhythm development, principal component analysis and signal superimposing imaging methods revealed a novel phasic pattern of BD-BT correlation day/night switching in animals older than postnatal day 38 (approximately equivalent to one year of age in humans). The origin of this switch was related to earlier development of body temperature (BT) rhythms and alteration of psychological behavior rhythms (BD) around earlier feeding times. We propose that this cost-effective, inclusive sensing and analytic technique has value for understanding developmental care conditions for which continual home non-invasive monitoring would be beneficial and further suggest the potential to adapt this technique for use in humans.

Dysregulation of behavioral and autonomic responses to emotional and social stimuli following bidirectional pharmacological manipulation of the basolateral amygdala in macaques

The amygdala is a key component of the neural circuits mediating the processing and response to emotionally salient stimuli. Amygdala lesions dysregulate social interactions, responses to fearful stimuli, and autonomic functions. In rodents, the basolateral and central nuclei of the amygdala have divergent roles in behavioral control. However, few studies have selectively examined these nuclei in the primate brain. Moreover, the majority of non-human primate studies have employed lesions, which only allow for unidirectional manipulation of amygdala activity. Thus, the effects of amygdala disinhibition on behavior in the primate are unknown. To address this gap, we pharmacologically inhibited by muscimol or disinhibited by bicuculline methiodide the basolateral complex of the amygdala (BLA; lateral, basal, and accessory basal) in nine awake, behaving male rhesus macaques (Macaca mulatta). We examined the effects of amygdala manipulation on: (1) behavioral responses to taxidermy snakes and social stimuli, (2) food competition and social interaction in dyads, (3) autonomic arousal as measured by cardiovascular response, and (4) prepulse inhibition of the acoustic startle (PPI) response. All modalities were impacted by pharmacological inhibition and/or disinhibition. Amygdala inhibition decreased fear responses to snake stimuli, increased examination of social stimuli, reduced competitive reward-seeking in dominant animals, decreased heart rate, and increased PPI response. Amygdala disinhibition restored fearful response after habituation to snakes, reduced competitive reward-seeking behavior in dominant animals, and lowered heart rate. Thus, both hypoactivity and hyperactivity of the basolateral amygdala can lead to dysregulated behavior, suggesting that a narrow range of activity is necessary for normal functions.

Noninvasive cardiac psychophysiology as a tool for translational science with marmosets

The importance of marmosets for comparative and translational science has grown in recent years because of their relatively rapid development, birth cohorts of twins, family social structure, and genetic tractability. Despite this, they remain understudied in investigations of affective processes. In this methodological note, we establish the validity of using noninvasive commercially available equipment to record cardiac physiology and compute indices of autonomic nervous system activity-a major component of affective processes. Specifically, we recorded electrocardiogram and impedance cardiogram, from which we derived heart rate, respiration rate, measures of high-frequency heart rate variability (indices of parasympathetic autonomic nervous system activity), and ventricular contractility (an index of sympathetic autonomic nervous system activity). Our methods produced physiologically plausible data, and further, animals with increased heart rates during testing were also more reactive to isolation from their social partner and presentation of novel objects, though no relationship was observed between reactivity and specific indices of parasympathetic or sympathetic nervous system activity.

Glutamate Within the Marmoset Anterior Hippocampus Interacts with Area 25 to Regulate the Behavioral and Cardiovascular Correlates of High-Trait Anxiety

High-trait anxiety is a risk factor for the development of affective disorders and has been associated with decreased cardiovascular and behavioral responsivity to acute stressors in humans that may increase the risk of developing cardiovascular disease. Although human neuroimaging studies of high-trait anxiety reveals dysregulation in primate cingulate areas 25 and 32 and the anterior hippocampus (aHipp) and rodent studies reveal the importance of aHipp glutamatergic hypofunction, the causal involvement of aHipp glutamate and its interaction with these areas in the primate brain is unknown. Accordingly, we correlated marmoset trait anxiety scores to their postmortem aHipp glutamate levels and showed that low glutamate in the right aHipp is associated with high-trait anxiety in marmosets. Moreover, pharmacologically increasing aHipp glutamate reduced anxiety levels in highly anxious marmosets in two uncertainty-based tests of anxiety: exposure to a human intruder with uncertain intent and unpredictable loud noise. In the human intruder test, increasing aHipp glutamate decreased anxiety by increasing approach to the intruder. In the unpredictable threat test, animals showed blunted behavioral and cardiovascular responsivity after control infusions, which was normalized by increasing aHipp glutamate. However, this aHipp-mediated anxiolytic effect was blocked by simultaneous pharmacological inactivation of area 25, but not area 32, areas which when inactivated independently reduced and had no effect on anxiety, respectively. These findings provide causal evidence in male and female primates that aHipp glutamatergic hypofunction and its regulation by area 25 contribute to the behavioral and cardiovascular symptoms of endogenous high-trait anxiety.SIGNIFICANCE STATEMENT High-trait anxiety predisposes sufferers to the development of anxiety and depression. Although neuroimaging of these disorders and rodent modeling implicate dysregulation in hippocampal glutamate and the subgenual/perigenual cingulate cortices (areas 25/32), the causal involvement of these structures in endogenous high-trait anxiety and their interaction are unknown. Here, we demonstrate that increased trait anxiety in marmoset monkeys correlates with reduced hippocampal glutamate and that increasing hippocampal glutamate release in high-trait-anxious monkeys normalizes the aberrant behavioral and cardiovascular responsivity to potential threats. This normalization was blocked by simultaneous inactivation of area 25, but not area 32. These findings provide casual evidence in primates that hippocampal glutamatergic hypofunction regulates endogenous high-trait anxiety and the hippocampal-area 25 circuit is a potential therapeutic target.

Fractionating Blunted Reward Processing Characteristic of Anhedonia by Over-Activating Primate Subgenual Anterior Cingulate Cortex

Anhedonia is a core symptom of depression, but the underlying neurobiological mechanisms are unknown. Correlative neuroimaging studies implicate dysfunction within ventromedial prefrontal cortex, but the causal roles of specific subregions remain unidentified. We addressed these issues by combining intracerebral microinfusions with cardiovascular and behavioral monitoring in marmoset monkeys to show that over-activation of primate subgenual anterior cingulate cortex (sgACC, area 25) blunts appetitive anticipatory, but not consummatory, arousal, whereas manipulations of adjacent perigenual ACC (pgACC, area 32) have no effect. sgACC/25 over-activation also reduces the willingness to work for reward. ¹⁸F-FDG PET imaging reveals over-activation induced metabolic changes in circuits involved in reward processing and interoception. Ketamine treatment ameliorates the blunted anticipatory arousal and reverses associated metabolic changes. These results demonstrate a causal role for primate sgACC/25 over-activity in selective aspects of impaired reward processing translationally relevant to anhedonia, and ketamine's modulation of an affective network to exert its action.

Appetitive drives for ultra-processed food products and the ability of text warnings to counteract consumption predispositions

OBJECTIVE

The present study aimed to (i) assess the appetitive drives evoked by the visual cues of ultra-processed food and drink products and (ii) investigate whether text warnings reduce appetitive drives and consumers' reported intentions to eat or drink ultra-processed products.

DESIGN

In Study I, a well-established psychometric tool was applied to estimate the appetitive drives associated with ultra-processed products using sixty-four image representations. Sixteen product types with four exemplars of a given product were included. Pictures from the International Affective Picture System (IAPS) served as controls. The two exemplars of each product type rated as more appetitive were selected for investigation in the second study. Study II assessed the impact of textual warnings on the appetitive drive towards these thirty-two exemplars. Each participant was exposed to two picture exemplars of the same product type preceded by a text warning or a control text. After viewing each displayed picture, the participants reported their emotional reactions and their intention to consume the product.

SETTING

Controlled classroom experiments SUBJECTS: Undergraduate students (Study I: n 215, 135 women; Study II: n 98, 52 women).

RESULTS

In Study I, the pictures of ultra-processed products prompted an appetitive motivation associated with the products' nutritional content. In Study II, text warnings were effective in reducing the intention to consume and the appetitive drive evoked by ultra-processed products.

CONCLUSIONS

This research provides initial evidence favouring the use of text warnings as a public policy tool to curb the powerful influence of highly appetitive ultra-processed food cues.

Converging Prefronto-Insula-Amygdala Pathways in Negative Emotion Regulation in Marmoset Monkeys

BACKGROUND

Impaired regulation of emotional responses to potential threat is a core feature of affective disorders. However, while the subcortical circuitry responsible for processing and expression of fear has been well characterized, the top-down control of this circuitry is less well understood. Our recent studies demonstrated that heightened emotionality, as measured both physiologically and behaviorally, during conditioned fear and innate/social threat was induced, independently, by excitotoxic lesions of either the anterior orbitofrontal cortex (antOFC) or ventrolateral prefrontal cortex (vlPFC). An important outstanding question is whether the antOFC and vlPFC act on common or distinct downstream targets to regulate negative emotion.

METHODS

The question was addressed by combining localized excitotoxic lesions in the PFC of a nonhuman primate and functional neuroimaging ([¹⁸F]fluorodeoxyglucose positron emission tomography) with a fear-regulating extinction paradigm. Marmoset monkeys with unilateral lesions of either the antOFC or vlPFC were scanned immediately following exposure to a fearful or safe context, and differences in [¹⁸F]fluorodeoxyglucose uptake were evaluated.

RESULTS

[¹⁸F]fluorodeoxyglucose uptake in the insula and amygdala of the intact hemisphere was significantly increased in response to the fearful context compared with the safe context. Such discrimination between the two contexts was not reflected in the activity of the insula-amygdala of the antOFC or vlPFC-lesioned hemisphere. Instead, uptake was at an intermediate level in both contexts.

CONCLUSIONS

These findings demonstrate that the distinct control functions of the antOFC and vlPFC converge on the same downstream targets to promote emotion regulation, taking us closer to a mechanistic understanding of different forms of anxiety.

Coping Style Modifies General and Affective Autonomic Reactions of Domestic Pigs in Different Behavioral Contexts

Based on individual adaptive strategies (coping), animals may react differently to environmental challenges in terms of behavior and physiology according to their emotional perception. Emotional valence as well as arousal may be derived by measuring vagal and sympathetic tone of the autonomic nervous system (ANS). We investigated the situation-dependent autonomic response of 16 domestic pigs with either a reactive or a proactive coping style, previously selected according to the backtest which is accepted in piglets to assess escape behavior. At 11 weeks of age, the pigs were equipped with an implantable telemetric device, and heart rate (HR), blood pressure (BP) and their respective variabilities (HRV, BPV) were recorded for 1 h daily over a time period of 10 days and analyzed in four behavioral contexts (resting, feeding, idling, handling). Additionally, the first minute of feeding and handling was used for a short-term analysis of these parameters in 10-s intervals. Data from day 1-3 (period 1) and day 8-10 (period 2) were grouped into two separate periods. Our results revealed general differences between the coping styles during feeding, resting and handling, with proactive pigs showing higher HR compared to reactive pigs. This elevated HR was based on either lower vagal (resting) or elevated sympathetic activation (feeding, handling). The short-term analysis of the autonomic activation during feeding revealed a physiological anticipation reaction in proactive pigs in period 1, whereas reactive pigs showed this reaction only in period 2. Food intake was characterized by sympathetic arousal with concurrent vagal withdrawal, which was more pronounced in proactive pigs. In contrast, neither coping style resulted in an anticipation reaction to handling. Vagal activation increased in reactive pigs during handling, while proactive pigs showed an increase in sympathetically driven arousal in period 2. Our findings confirm significant context-related differences in the general autonomic reaction of pigs with different coping styles. Additionally, the two coping styles differ in their affective appraisal over the time course of the experiment, underlining the importance of taking individual differences into account when studying affect and emotion in humans and animals.

Opposing roles of primate areas 25 and 32 and their putative rodent homologs in the regulation of negative emotion

Disorders of dysregulated negative emotion such as depression and anxiety also feature increased cardiovascular mortality and decreased heart-rate variability (HRV). These disorders are correlated with dysfunction within areas 25 and 32 of the ventromedial prefrontal cortex (vmPFC), but a causal relationship between dysregulation of these areas and such symptoms has not been demonstrated. Furthermore, cross-species translation is limited by inconsistent findings between rodent fear extinction and human neuroimaging studies of negative emotion. To reconcile these literatures, we applied an investigative approach to the brain-body interactions at the core of negative emotional dysregulation. We show that, in marmoset monkeys (a nonhuman primate that has far greater vmPFC homology to humans than rodents), areas 25 and 32 have causal yet opposing roles in regulating the cardiovascular and behavioral correlates of negative emotion. In novel Pavlovian fear conditioning and extinction paradigms, pharmacological inactivation of area 25 decreased the autonomic and behavioral correlates of negative emotion expectation, whereas inactivation of area 32 increased them via generalization. Area 25 inactivation also increased resting HRV. These findings are inconsistent with current theories of rodent/primate prefrontal functional similarity, and provide insight into the role of these brain regions in affective disorders. They demonstrate that area 32 hypoactivity causes behavioral generalization relevant to anxiety, and that area 25 is a causal node governing the emotional and cardiovascular symptomatology relevant to anxiety and depression.

Using pupil size and heart rate to infer affective states during behavioral neurophysiology and neuropsychology experiments

BACKGROUND

Nonhuman primates (NHPs) are a valuable research model because of their behavioral, physiological and neuroanatomical similarities to humans. In the absence of language, autonomic activity can provide crucial information about cognitive and affective states during single-unit recording, inactivation and lesion studies. Methods standardized for use in humans are not easily adapted to NHPs and detailed guidance has been lacking.

NEW METHOD

We provide guidance for monitoring heart rate and pupil size in the behavioral neurophysiology setting by addressing the methodological issues, pitfalls and solutions for NHP studies. The methods are based on comparative physiology to establish a rationale for each solution. We include examples from both electrophysiological and lesion studies.

RESULTS

Single-unit recording, pupil responses and heart rate changes represent a range of decreasing temporal resolution, a characteristic that impacts experimental design and analysis. We demonstrate the unexpected result that autonomic measures acquired before and after amygdala lesions are comparable despite disruption of normal autonomic function.

COMPARISON WITH EXISTING METHODS

Species and study design differences can render standard techniques used in human studies inappropriate for NHP studies. We show how to manage data from small groups typical of NHP studies, data from the short behavioral trials typical of neurophysiological studies, issues associated with longitudinal studies, and differences in anatomy and physiology.

CONCLUSIONS

Autonomic measurement to infer cognitive and affective states in NHP is neither off-the-shelf nor onerous. Familiarity with the issues and solutions will broaden the use of autonomic signals in NHP single unit and lesion studies.

A dimensional approach to modeling symptoms of neuropsychiatric disorders in the marmoset monkey

Some patients suffering from the same neuropsychiatric disorder may have no overlapping symptoms whilst others may share symptoms common to other distinct disorders. Therefore, the Research Domain Criteria initiative recognises the need for better characterisation of the individual symptoms on which to focus symptom-based treatment strategies. Many of the disorders involve dysfunction within the prefrontal cortex (PFC) and so the marmoset, due to their highly developed PFC and small size, is an ideal species for studying the neurobiological basis of the behavioural dimensions that underlie these symptoms.Here we focus on a battery of tests that address dysfunction spanning the cognitive (cognitive inflexibility and working memory), negative valence (fear generalisation and negative bias) and positive valence (anhedonia) systems pertinent for understanding disorders such as ADHD, Schizophrenia, Anxiety, Depression and OCD. Parsing the separable prefrontal and striatal circuits and identifying the selective neurochemical modulation (serotonin vs dopamine) that underlie cognitive dysfunction have revealed counterparts in the clinical domain. Aspects of the negative valence system have been explored both at individual- (trait anxiety and genetic variation in serotonin transporter) and circuit-based levels enabling the understanding of generalisation processes, negative biases and differential responsiveness to SSRIs. Within the positive valence system, the combination of cardiovascular and behavioural measures provides a framework for understanding motivational, anticipatory and consummatory aspects of anhedonia and their neurobiological mechanisms. Together, the direct comparison of experimental findings in marmosets with clinical studies is proving an excellent translational model to address the behavioural dimensions and neurobiology of neuropsychiatric symptoms. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 328-353, 2017.

Metabolic activation of amygdala, lateral septum and accumbens circuits during food anticipatory behavior

When food is restricted to a brief fixed period every day, animals show an increase in temperature, corticosterone concentration and locomotor activity for 2-3h before feeding time, termed food anticipatory activity. Mechanisms and neuroanatomical circuits responsible for food anticipatory activity remain unclear, and may involve both oscillators and networks related to temporal conditioning. Rabbit pups are nursed once-a-day so they represent a natural model of circadian food anticipatory activity. Food anticipatory behavior in pups may be associated with neural circuits that temporally anticipate feeding, while the nursing event may produce consummatory effects. Therefore, we used New Zealand white rabbit pups entrained to circadian feeding to investigate the hypothesis that structures related to reward expectation and conditioned emotional responses would show a metabolic rhythm anticipatory of the nursing event, different from that shown by structures related to reward delivery. Quantitative cytochrome oxidase histochemistry was used to measure regional brain metabolic activity at eight different times during the day. We found that neural metabolism peaked before nursing, during food anticipatory behavior, in nuclei of the extended amygdala (basolateral, medial and central nuclei, bed nucleus of the stria terminalis), lateral septum and accumbens core. After pups were fed, however, maximal metabolic activity was expressed in the accumbens shell, caudate, putamen and cortical amygdala. Neural and behavioral activation persisted when animals were fasted by two cycles, at the time of expected nursing. These findings suggest that metabolic activation of amygdala-septal-accumbens circuits involved in temporal conditioning may contribute to food anticipatory activity.

Behavioural and physiological measures indicate subtle variations in the emotional valence of young pigs

In the study of animal emotions, emotional valence has been found to be difficult to measure. Many studies of farm animals' emotions have therefore focussed on the identification of indicators of strong, mainly negative, emotions. However, subtle variations in emotional valence, such as those caused by rather moderate differences in husbandry conditions, may also affect animals' mood and welfare when such variations occur consistently. In this study, we investigated whether repeated moderate aversive or rewarding events could lead to measurable differences in emotional valence in young, weaned pigs. We conditioned 105 female pigs in a test arena to either a repeated startling procedure (sudden noises or appearances of objects) or a repeated rewarding procedure (applesauce, toy and straw) over 11 sessions. Control pigs were also regularly exposed to the same test arena but without conditioning. Before and after conditioning, we measured heart rate and its variability as well as the behavioural reactions of the subjects in the test arena, with a special focus on detailed acoustic analyses of their vocalisations. The behavioural and heart rate measures were analysed as changes compared to the baseline values before conditioning. A limited number of the putative indicators of emotional valence were affected by the conditioning. We found that the negatively conditioned pigs showed changes that were significantly different from those in control pigs, namely a decrease in locomotion and an increase in standing. The positively conditioned pigs, however, showed a stronger increase in heart rate and a smaller decrease in SDNN (a heart rate variability parameter indicating changes in autonomic regulation) compared to the controls. Compared to the negatively conditioned pigs, the positively conditioned pigs produced fewer vocalisations overall as well as fewer low-frequency grunts but more high-frequency grunts. The low-frequency grunts of the negatively conditioned pigs also showed lower frequency parameters (bandwidth, maximum frequency, 25% and 50% quartiles) compared to those of the positively conditioned pigs. In any of the statistically significant results, the conditioning accounted for 1.5-11.9% of variability in the outcome variable. Hence, we conclude that repeated moderate aversive and rewarding events have weak but measurable effects on some aspects of behaviour and physiology in young pigs, possibly indicating changes in emotional valence, which could ultimately affect their welfare. The combination of ethophysiological indicators, i.e., the concurrent examination of heart rate measures, behavioural responses and especially vocalisation patterns, as used in the current study, might be a useful way of examining subtle effects on emotional valence in further studies.

Assessing positive emotional states in dogs using heart rate and heart rate variability

Since most animal species have been recognized as sentient beings, emotional state may be a good indicator of welfare in animals. The goal of this study was to manipulate the environment of nine beagle research dogs to highlight physiological responses indicative of different emotional experiences. Stimuli were selected to be a more or a less positive food (meatball or food pellet) or social reward (familiar person or less familiar person). That all the stimuli were positive and of different reward value was confirmed in a runway motivation test. Dogs were tested individually while standing facing a display theatre where the different stimuli could be shown by lifting a shutter. The dogs approached and remained voluntarily in the test system. They were tested in four sessions (of 20s each) for each of the four stimuli. A test session consisted of four presentation phases (1st exposure to stimulus, post exposure, 2nd exposure, and access to reward). Heart rate (HR) and heart rate variability (HRV) responses were recorded during testing in the experimental room and also when lying resting in a quiet familiar room. A new method of 'stitching' short periods of HRV data together was used in the analysis. When testing different stimuli, no significant differences were observed in HR and LF:HF ratio (relative power in low frequency (LF) and the high-frequency (HF) range), implying that the sympathetic tone was activated similarly for all the stimuli and may suggest that dogs were in a state of positive arousal. A decrease of HF was associated with the meatball stimulus compared to the food pellet and the reward phase (interacting with the person or eating the food) was associated with a decrease in HF and RMSSD (root mean square of successive differences of inter-beat intervals) compared to the preceding phase (looking at the person or food). This suggests that parasympathetic deactivation is associated with a more positive emotional state in the dog. A similar reduction in HF and RMSSD was found in the test situation compared to the resting situation. This is congruent with the expected autonomic effects related to postural shift i.e. sympathetic activation and parasympathetic withdrawal, during standing versus lying, but it cannot explain the parasympathetic deactivation in response to the more positive stimuli since the dogs were always standing in the test situation. We discuss the systematic pattern of responses, which support that increased HR and LF:HF ratio are associated with emotional arousal, but add the new proposal that a combined decrease in RMSSD and HF may reflect a more positively valenced emotional state even when an individual is already in a positive psychological state.

Anticipation and frequency of feeding affect heart reactions in domestic pigs

Measuring heart reactions has become a widely used method for the assessment of emotions. Heart rate and its variability, which can quite easily be noninvasively recorded, reflect the inputs of the sympathetic and parasympathetic branches of the autonomous nervous system. We tested the hypothesis that frequent anticipation of a positive event results in an increased state of welfare in pigs, expressed as positive arousal in anticipation of announced feeding as well as lowered heart rate and augmented heart rate variability during resting periods. We used a controlled paradigm with 3 groups of young domestic pigs (Sus scrofa domestica). We compared frequent acoustic announcement of feed delivery (group 1: 3 feedings between 0730 h and 1030 h plus 3 feedings between 1200 h and 1530 h) with the same number of feedings as in group 1 but without a temporal relation to the sound (group 2) and with a fixed-schedule feeding (group 3: 2 feedings at 0600 h and 1500 h). Specific cardiac and behavioral reactions indicated short-term (1 min) anticipation in the conditioned group. In this group, heart rate increased (P < 0.001) mainly through vagal withdraw and behavior became more active (P < 0.001). Only the conditioned group displayed changing heart rate characteristics during the sound. Pigs in the frequent unpredictable feed group reacted to feed delivery with increased heart rates (P < 0.001), whereas the heart-rate characteristics of pigs with the fixed schedule were unchanged during the sound and while the other 2 treatment groups were feeding. Clear evidence for long-term anticipation (over the course of hours) was not present in the data. Comparisons between the 3 treatment groups suggested that in housing conditions where pigs cannot obtain feed by their actions but must wait for feed delivery, feeding at 2 fixed times would be preferred. Animals in this treatment group presented lower resting heart rates at the end of the experiment than animals in the other 2 groups (P < 0.01). Therefore, merely announcing a positive stimulus without giving control to its access is apparently not suitable for increasing welfare.

Scratching under positive and negative arousal in common marmosets (Callithrix jacchus)

Scratching has been widely used as an indicator of anxiety in many primate species. However, a handful of studies have shown no change in scratching under anxiety-provoking circumstances. In addition, the existing literature has investigated scratching only in relation to negative arousal (i.e., anxiety), even though anxiety and excitement (positive arousal) share important physiological and behavioral correlates, including increased heart rate, blood pressure, and locomotion. In the current study, we scored all instances of scratching in 11 outdoor-housed captive common marmosets (Callithrix jacchus) during three contexts that were intended to be negatively arousing and three contexts that were intended to be positively arousing during a baseline, manipulation, and post-induction period. Summed across the three negative arousal contexts, the results showed that subjects exhibited significantly lower scratching rates during the manipulation than during either the baseline or post-induction periods, and the pattern of means was the same for all three of those contexts. Under the three contexts of positive arousal, subjects exhibited different patterns of scratching rates during the manipulation periods (play = increases, foraging = decreases, food anticipation = no change). Data from the current study, and a close examination of data from studies showing no change in scratching under anxiety-provoking circumstances, suggest that the anxiety-scratching relationship may be more complex than has been reported previously. Our results raise a potential concern about the unchallenged use of scratching as a behavioral indicator of anxiety in captive non-human primates, with important implications for welfare and management of these species.

Can vocal conditioning trigger a semiotic ratchet in marmosets?

The complexity of human communication has often been taken as evidence that our language reflects a true evolutionary leap, bearing little resemblance to any other animal communication system. The putative uniqueness of the human language poses serious evolutionary and ethological challenges to a rational explanation of human communication. Here we review ethological, anatomical, molecular, and computational results across several species to set boundaries for these challenges. Results from animal behavior, cognitive psychology, neurobiology, and semiotics indicate that human language shares multiple features with other primate communication systems, such as specialized brain circuits for sensorimotor processing, the capability for indexical (pointing) and symbolic (referential) signaling, the importance of shared intentionality for associative learning, affective conditioning and parental scaffolding of vocal production. The most substantial differences lie in the higher human capacity for symbolic compositionality, fast vertical transmission of new symbols across generations, and irreversible accumulation of novel adaptive behaviors (cultural ratchet). We hypothesize that increasingly-complex vocal conditioning of an appropriate animal model may be sufficient to trigger a semiotic ratchet, evidenced by progressive sign complexification, as spontaneous contact calls become indexes, then symbols and finally arguments (strings of symbols). To test this hypothesis, we outline a series of conditioning experiments in the common marmoset (Callithrix jacchus). The experiments are designed to probe the limits of vocal communication in a prosocial, highly vocal primate 35 million years far from the human lineage, so as to shed light on the mechanisms of semiotic complexification and cultural transmission, and serve as a naturalistic behavioral setting for the investigation of language disorders.

Assessing value representation in animals

Among all factors modulating our motivation to perform a given action, the ability to represent its outcome is clearly the most determining. Representation of outcomes, rewards in particular, and how they guide behavior, have sparked much research. Both practically and theoretically, understanding the relationship between the representation of outcome value and the organization of goal directed behavior implies that these two processes can be assessed independently. Most of animal studies essentially used instrumental actions as a proxy for the expected goal-value. The purpose of this article is to consider alternative measures of expected outcome value in animals, which are critical to understand the behavioral and neurobiological mechanisms relating the representation of the expected outcome to the organization of the behavior oriented towards its obtention. This would be critical in the field of decision making or social interactions, where the value of multiple items must often be compared and/or shared among individuals to determine the course of actions.

Individual differences in behavioral and cardiovascular reactivity to emotive stimuli and their relationship to cognitive flexibility in a primate model of trait anxiety

High trait anxiety is a risk factor for the development of anxiety disorders. Like the disorders themselves high trait anxiety has marked phenotypic variation at the level of symptomatology and neural circuits, suggesting that there may be different symptoms and distinct neural circuits associated with risk for these disorders. To address these issues, it is essential to develop reliable animal models of trait anxiety in a non-human primate whose brain bears structural and functional similarity to humans. The present study investigated individual variation in responsivity to fearful and anxiety provoking stimuli in the common marmoset monkey. Seven out of 27 animals failed to display discriminative, conditioned cardiovascular and behavioral responses on an auditory fear discrimination task, similar to that seen in high anxious humans and rodents. Their heightened emotionality to a rubber snake was consistent with the hypothesis that they were high in trait-like anxiety. Evidence for phenotypic variation in the high anxiety group was provided by the finding that discrimination failure was predicted early in conditioning by either hyper-vigilant scanning to the cues or a reduction in blood pressure to the context, i.e., test apparatus. Given that high trait anxiety in humans can be associated with altered prefrontal cognitive functioning and previously we implicated the marmoset anterior orbitofrontal (antOFC) and ventrolateral prefrontal cortex (vlPFC) in negative emotion regulation, we also tested the marmosets on two tests of cognitive flexibility differentially dependent on these two regions. While the high anxious group did not differ overall in their perseverative performance, the two distinct phenotypes were differentially correlated with reduced perseverative responding on the OFC- and vlPFC-dependent flexibility tests. Together, this study provides a new model of trait anxiety in marmosets amenable to analysis of phenotypic variation and neural circuitry.

A role for primate subgenual cingulate cortex in sustaining autonomic arousal

The subgenual anterior cingulate cortex (subgenual ACC) plays an important role in regulating emotion, and degeneration in this area correlates with depressed mood and anhedonia. Despite this understanding, it remains unknown how this part of the prefrontal cortex causally contributes to emotion, especially positive emotions. Using Pavlovian conditioning procedures in macaque monkeys, we examined the contribution of the subgenual ACC to autonomic arousal associated with positive emotional events. After such conditioning, autonomic arousal increases in response to cues that predict rewards, and monkeys maintain this heightened state of arousal during an interval before reward delivery. Here we show that although monkeys with lesions of the subgenual ACC show the initial, cue-evoked arousal, they fail to sustain a high level of arousal until the anticipated reward is delivered. Control procedures showed that this impairment did not result from differences in autonomic responses to reward delivery alone, an inability to learn the association between cues and rewards, or to alterations in the light reflex. Our data indicate that the subgenual ACC may contribute to positive affect by sustaining arousal in anticipation of positive emotional events. A failure to maintain positive affect for expected pleasurable events could provide insight into the pathophysiology of psychological disorders in which negative emotions dominate a patient's affective experience.

Effects of cognitive enrichment on behavioural and physiological reactions of pigs

Cognitive enrichment, a special form of environmental enrichment, addresses the cognitive abilities of animals in captivity. Through cognitive interaction with the environment, the animals regain a certain control over their environment, and essential resources, such as food or water, act as a reward for successful coping. It is assumed that this process has important implications for animal welfare, especially in the intensive housing systems of farm animals. This study investigates the effects of cognitive enrichment on welfare-relevant behaviour (agonistic interactions and behavioural reactivity in a repeated open-field test) and autonomic control (heart rate variability during feeding, resting and in a repeated open-field test) in domestic pigs. A total of forty-eight pigs, Sus scrofa, were housed in groups of four. In six replicates, an experimental group was compared with a conventionally fed control group. The pigs in the experimental group were confronted with a cognitive challenge that was integrated into their familiar housing environment. Pigs were rewarded with food after they successfully mastered the discrimination of an individual acoustical signal followed by an operant task. The pigs in both groups reacted with sympathetic arousal to feeding announcement (increased heart rate (HR)). During feeding, the experimental pigs' HR decreased, and heart rate variability (HRV) increased, while the control pigs' HR stayed highly elevated and HRV decreased. These results are supported by a considerably larger number of agonistic interactions during feeding in the control group. During resting, the basal HRV of the experimental pigs increased (during operant conditioning) compared to the control. In the repeated open-field test, the experimental pigs displayed less locomotion and elimination as well as more contact with the wall and an unknown object compared to the control group. We conclude that cognitive enrichment leads to relaxed feeding and evokes longer lasting positive emotions. Moreover, the pigs displayed more explorative and less fearful behaviour in stressful situations. These findings support the use of cognitive enrichment to improve animal welfare.

Prefrontal cortex activity, sympatho-vagal reaction and behaviour distinguish between situations of feed reward and frustration in dwarf goats

Recent concepts relating to animal welfare accept that animals experience affective states. These are notoriously difficult to measure in non-verbal species, but it is generally agreed that emotional reactions consist of well-coordinated reactions in behaviour, autonomic and brain activation. The aim of the study was to evaluate whether each or a combination of these aspects can differentiate between situations presumed to differ in emotional content. To this end, we repeatedly confronted dwarf goats at short intervals with a covered and an uncovered feed bowl (i.e. presumably frustrating and rewarding situations respectively) whilst simultaneously observing their behaviour, measuring heart-rate and heart-rate variability and haemodynamic changes in the prefrontal cortex using functional near-infrared spectroscopy. When faced with a covered feed bowl, goats occupied themselves at locations away from the bowl and showed increased locomotion, while there was a general increase in prefrontal cortical activity. There was little indication of autonomic changes. In contrast, when feed was accessible, the goats reduced locomotion, focused their behaviour on the feed bowl, showed signs of sympathetically mediated arousal reflecting anticipation and, if any cortical activity at all was present, it was concentrated to the left hemisphere. We thus observed patterns in behaviour, sympathetic reaction and brain activity that distinguished between a situation of frustration and one of reward in dwarf goats. These patterns consisted of a well-coordinated set of reactions appropriate in respect of the emotional content of the stimuli used.

Lesions of ventrolateral prefrontal or anterior orbitofrontal cortex in primates heighten negative emotion

BACKGROUND

Heightened fear and anxiety are core symptoms of a variety of neuropsychiatric disorders. They are associated with structural and activity changes throughout neural circuitry that includes the ventral and medial prefrontal cortices (PFC), the amygdala, and hippocampus. Although the contributions of the medial PFC, amygdala, and hippocampus to fear and anxiety have been studied extensively with animal models, the selective roles of the ventral PFC-including the ventrolateral prefrontal cortex (vlPFC) and orbitofrontal cortex-are poorly understood.

METHODS

We investigated the effects of selective excitotoxic lesions of either the vlPFC or anterior orbitofrontal cortex (antOFC) on anxious behavior and Pavlovian conditioned autonomic and behavioral fear responses in the New World primate, the common marmoset.

RESULTS

Both vlPFC and antOFC lesions resulted in stronger, less adaptable conditioned fear responses. They also heightened the anxiety responses of a marmoset to a human intruder. In contrast, only a lesion of the vlPFC affected the coping style that a marmoset displayed in the presence of the human intruder, increasing the likelihood of proactive mobbing.

CONCLUSIONS

These results suggest that both the antOFC and vlPFC can downregulate fear and anxiety and, together, provide necessary but independent contributions to the top-down control of negative emotion.

Angiotensin type 1A receptors in C1 neurons of the rostral ventrolateral medulla modulate the pressor response to aversive stress

The rise in blood pressure during an acute aversive stress has been suggested to involve activation of angiotensin type 1A receptors (AT(1A)Rs) at various sites within the brain, including the rostral ventrolateral medulla. In this study we examine the involvement of AT(1A)Rs associated with a subclass of sympathetic premotor neurons of the rostral ventrolateral medulla, the C1 neurons. The distribution of putative AT(1A)R-expressing cells was mapped throughout the brains of three transgenic mice with a bacterial artificial chromosome-expressing green fluorescent protein under the control of the AT(1A)R promoter. The overall distribution correlated with that of the AT(1A)Rs mapped by other methods and demonstrated that the majority of C1 neurons express the AT(1A)R. Cre-recombinase expression in C1 neurons of AT(1A)R-floxed mice enabled demonstration that the pressor response to microinjection of angiotensin II into the rostral ventrolateral medulla is dependent upon expression of the AT(1A)R in these neurons. Lentiviral-induced expression of wild-type AT(1A)Rs in C1 neurons of global AT(1A)R knock-out mice, implanted with radiotelemeter devices for recording blood pressure, modulated the pressor response to aversive stress. During prolonged cage-switch stress, expression of AT(1A)Rs in C1 neurons induced a greater sustained pressor response when compared to the control viral-injected group (22 ± 4 mmHg for AT(1A)R vs 10 ± 1 mmHg for GFP; p < 0.001), which was restored toward that of the wild-type group (28 ± 2 mmHg). This study demonstrates that AT(1A)R expression by C1 neurons is essential for the pressor response to angiotensin II and that this pathway plays an important role in the pressor response to aversive stress.

Serotonin at the level of the amygdala and orbitofrontal cortex modulates distinct aspects of positive emotion in primates

Impaired top-down regulation of the amygdala, and its modulation by serotonin (5-HT), is strongly implicated in the dysregulation of negative emotion that characterizes a number of affective disorders. However, the contribution of these mechanisms to the regulation of positive emotion is not well understood. This study investigated the role of 5-HT within the amygdala and the orbitofrontal cortex (OFC), on the expression of appetitive Pavlovian conditioned emotional responses and their reversal in a primate, the common marmoset. Its effects were compared to those of the amygdala itself. Having developed conditioned autonomic and behavioural responses to an appetitive cue prior to surgery, marmosets with excitotoxic amygdala lesions failed to display such conditioned autonomic arousal at retention, but still displayed intact cue-directed conditioned behaviours. In contrast, 5,7-DHT infusions into the amygdala, reducing extracellular 5-HT levels, selectively enhanced the expression of appetitive conditioned behaviour at retention. Similar infusions into the OFC, producing marked reductions in post-mortem 5-HT tissue levels, had no overall effect on autonomic or behavioural responses, either at retention or during reversal learning, but caused an uncoupling of these responses, thereby fractionating emotional output. These data demonstrate the critical role of the amygdala in the expression of appetitive autonomic conditioning, and the region-selective contribution of 5-HT in the amygdala and OFC, respectively, to the expression of conditioned behaviour and the overall coordination of the emotional response. They provide insight into the neurochemical mechanisms underlying the regulation of positive emotional responses, advancing our understanding of the neural basis of pathologically dysregulated emotion.

The amygdala as a target for behavior surgery

The amygdala was a popular target during the era of psychosurgery, specifically for the treatment of intractable aggression. This mesiotemporal structure was thought to primarily mediate fear and anger. However, recent evidence suggests that the amygdala is part of a complex network that mediates the formation of a larger repertoire of positive and negative emotions. Dysfunctions within the network or the amygdala itself can lead to various mental illnesses. In those cases, deep brain stimulation (DBS) applied focally may treat the symptoms. This review presents data supporting the potential therapeutic role of DBS of the amygdala in the treatment of anxiety disorders, addiction, and mood disorders. The success of DBS for psychiatric conditions will likely depend on our ability to precisely determine the optimal target for a specific case.

Challenges of Interpreting Frontal Neurons during Value-Based Decision-Making

The frontal cortex is crucial to sound decision-making, and the activity of frontal neurons correlates with many aspects of a choice, including the reward value of options and outcomes. However, rewards are of high motivational significance and have widespread effects on neural activity. As such, many neural signals not directly involved in the decision process can correlate with reward value. With correlative techniques such as electrophysiological recording or functional neuroimaging, it can be challenging to distinguish neural signals underlying value-based decision-making from other perceptual, cognitive, and motor processes. In the first part of the paper, we examine how different value-related computations can potentially be confused. In particular, error-related signals in the anterior cingulate cortex, generated when one discovers the consequences of an action, might actually represent violations of outcome expectation, rather than errors per se. Also, signals generated at the time of choice are typically interpreted as reflecting predictions regarding the outcomes associated with the different choice alternatives. However, these signals could instead reflect comparisons between the presented choice options and previously presented choice alternatives. In the second part of the paper, we examine how value signals have been successfully dissociated from saliency-related signals, such as attention, arousal, and motor preparation in studies employing outcomes with both positive and negative valence. We hope that highlighting these issues will prove useful for future studies aimed at disambiguating the contribution of different neuronal populations to choice behavior.

Brain angiotensin AT1 receptors as specific regulators of cardiovascular reactivity to acute psychoemotional stress

1. Cardiovascular reactivity, an abrupt rise in blood pressure (BP) and heart rate in response to psychoemotional stress, is a risk factor for heart disease. Pharmacological and molecular genetic studies suggest that brain angiotensin (Ang) II and AT(1) receptors are required for the normal expression of sympathetic cardiovascular responses to various psychological stressors. Moreover, overactivity of the brain AngII system may contribute to enhanced cardiovascular reactivity in hypertension. 2. Conversely, brain AT(1) receptors appear to be less important for the regulation of sympathetic cardiovascular responses to a range of stressors involving an immediate physiological threat (physical stressors) in animal models. 3. Apart from threatening events, appetitive stimuli can induce a distinct, central nervous system-mediated rise in BP. However, evidence indicates that brain AT(1) receptors are not essential for the regulation of cardiovascular arousal associated with positively motivated behaviour, such as anticipation and the consumption of palatable food. The role of central AT(1) receptors in regulating cardiovascular activation elicited by other types of appetitive stimuli remains to be determined. 4. Emerging evidence also indicates that brain AT(1) receptors play a limited role in the regulation of cardiovascular responses to non-emotional natural daily activities, sleep and exercise. 5. Collectively, these findings suggest that, with respect to cardiovascular arousal, central AT(1) receptors may be involved primarily in the regulation of the defence response. Therefore, these receptors could be a potential therapeutic target for selective attenuation of BP hyperreactivity to aversive stressors, without altering physiologically important cardiovascular adjustments to normal daily activities, sleep and exercise.

Localization of dysfunction in major depressive disorder: prefrontal cortex and amygdala

Despite considerable effort, the localization of dysfunction in major depressive disorder (MDD) remains poorly understood. We present a hypothesis about its localization that builds on recent findings from primate neuropsychology. The hypothesis has four key components: a deficit in the valuation of "self" underlies the core disorder in MDD; the medial frontal cortex represents "self"; interactions between the amygdala and cortical representations update their valuation; and inefficiency in using positive feedback by orbital prefrontal cortex contributes to MDD.

Interactions between orbital prefrontal cortex and amygdala: advanced cognition, learned responses and instinctive behaviors

Recent research indicates that the orbital prefrontal cortex (PFo) represents stimulus valuations and that the amygdala updates these valuations. An exploration of how PFo and the amygdala interact could improve the understanding of both. PFo and the amygdala function cooperatively when monkeys choose objects associated with recently revalued foods. In other tasks, they function in opposition. PFo uses positive feedback to promote learning in object-reward reversal tasks, and PFo also promotes extinction learning. Amygdala function interferes with both kinds of learning. The amygdala underlies fearful responses to a rubber snake from the first exposure on, but PFo is necessary only after the initial exposure. The amygdala mediates an arousal response in anticipation of rewards, whereas PFo sometimes suppresses such arousal. A role for PFo in advanced cognition, for the amygdala in instinctive behavior, and for cortex-subcortex interactions in prioritizing behaviors provides one account for these findings.