Measuring appetitive conditioned responses in humans

Implementations of sign- and goal-tracking behavior in humans: A scoping review

Animal research has identified two major phenotypes in the tendency to attribute incentive salience to a reward-associated cue. Individuals called "sign-trackers" (STs) preferentially approach the cue, assigning both predictive and incentive values to it. In contrast, individuals called "goal-trackers" (GTs) preferentially approach the location of the upcoming reward, assigning only a predictive value to the cue. The ST/GT model has been shown to be relevant to understanding addiction vulnerability and other pathological behaviors in animals. Therefore, recent studies tried to implement this animal model in the human population. This scoping review aimed to identify and map evidence of human sign- and goal-tracking. Studies that explicitly measured human sign- and goal-tracking or related phenomena (e.g., attentional bias induced by reward-related cues), using paradigms in line with the animal model, were eligible for this review. We searched for published, unpublished, and gray literature (PhD theses, posters, conference papers) through the following databases: MEDLINE, Scopus, PsycINFO, Embase, OSF, and Google Scholar. The JBI scoping review methodology was adopted. Screening and extraction were carried out by three reviewers, in pairs. A total of 48 studies were identified. These studies used various experimental paradigms and used the term "sign-tracking" inconsistently, sometimes implicitly or not at all. We conclude that the literature on human sign-tracking is very heterogeneous on many levels. Overall, evidence supports the existence of sign- and goal-tracking behaviors in humans, although further validated research is crucially needed.

Aversive conditioning is impaired in impulsive individuals: A study on learning asymmetries

BACKGROUND AND OBJECTIVES

Appetitive and aversive conditioning are thought to be involved in the development and maintenance of mental disorders including anxiety, mood, eating, and substance use disorders. However, few studies measure the relative strength of appetitive and aversive associations, and their relevance to the risk of mental disorders. This study aims to address this gap.

METHODS

We tested how readily healthy volunteers acquire appetitive vs. aversive associations. 150 participants associated complex 3D objects with either gain or loss and made decisions to gain or avoid losing points. We investigated the relationship of a learning asymmetry with neuroticism, impulsivity, and anhedonia, to test the hypothesis that a stronger learning asymmetry corresponds to more extreme scores on these traits.

RESULTS

Impulsivity was positively associated with the learning asymmetry (R2 = .10). This resulted from an inverse relation with the strength of aversive associations, indicating that impulsive individuals are worse at aversive learning. However, appetitive associations did not differ significantly. No correlations with neuroticism or anhedonia were found.

LIMITATIONS

Conditioning studies typically use primary reinforcers and a CS-. Lacking these may make these results less comparable to other studies.

CONCLUSIONS

We demonstrate that the learning asymmetry can measure individual differences linked to personality traits, and that impulsivity, normally linked with appetitive learning, also influences aversive learning. These results enable additional studies of learning asymmetry in relation to mental disorders, which could include measurements of mental health symptoms to provide further insight into how appetitive and aversive learning interacts with mental disorders.

Risk-promoting effects of reward-paired cues in human sign- and goal-trackers

Animal research suggests trait-like individual variation in the degree of incentive salience attribution to reward-predictive cues, defined phenotypically as sign-tracking (high) and goal-tracking (low incentive salience attribution). While these phenotypes have been linked to addiction features in rodents, their translational validity is less clear. Here, we examined whether sign- and goal-tracking in healthy human volunteers modulates the effects of reward-paired cues on decision making. Sign-tracking was measured in a Pavlovian conditioning paradigm as the amount of eye gaze fixation on the reward-predictive cue versus the location of impending reward delivery. In Study 1 (Cherkasova et al., 2018), participants were randomly assigned to perform a binary choice task in which rewards were either accompanied (cued, n = 63) or unaccompanied (uncued, n = 68) by money images and casino jingles. In Study 2, participants (n = 58) performed cued and uncued versions of the task in a within-subjects design. Across both studies, cues promoted riskier choice. Sign-tracking was not associated with risky choice in either study. Goal-tracking rather than sign-tracking was significantly associated with greater risk-promoting effects of cues in Study 1 but not in Study 2, although the direction of findings was consistent across both studies. These findings are at odds with the notion of sign-trackers being preferentially susceptible to the influence of reward cues on behavior and point to the role of mechanisms besides incentive salience in mediating such influences.

Neural correlates of naturalistic single-trial appetitive conditioning

BACKGROUND

Prior research suggests naturalistic single-trial appetitive conditioning may be a potent phenomenon in humans, capable of modulating both motivation and attention. In this study, we aimed to characterise the neural correlates of this phenomenon using functional Magnetic Resonance Imaging (fMRI) paradigms METHODS: Twenty-three healthy adults (12 males) underwent conditioning during which they ate a novel 3D object made from white chocolate (CS+) and handled a similar object made from plastic (CS-). Brain activity was recorded before and after conditioning during a passive viewing paradigm RESULTS: A naturalistic CS+ was rated as more highly craved, better-liked and elicited greater expectancies for chocolate than the CS- after conditioning. An exploration of the interaction between time (pre- and post-conditioning) and CS type (CS+, CS-) during the passive viewing task suggested enhanced activation from pre- to post-conditioning in the right superior frontal gyrus (R.SFG) in response to the CS-.

CONCLUSION

Results reveal neural correlates of single-trial appetitive conditioning and highlight a possible role of response inhibition during learning about non-rewards, perhaps optimizing motivated behaviour. These findings contribute to our understanding of the neural mechanisms underpinning rapid reward and non-reward learning, and may inform development of behavioural interventions for reward-driven overeating.

VR for Studying the Neuroscience of Emotional Responses

Emotions are frequently considered as the driving force of behavior, and psychopathology is often characterized by aberrant emotional responding. Emotional states are reflected on a cognitive-verbal, physiological-humoral, and motor-behavioral level but to date, human research lacks an experimental protocol for a comprehensive and ecologically valid characterization of such emotional states. Virtual reality (VR) might help to overcome this situation by allowing researchers to study mental processes and behavior in highly controlled but reality-like laboratory settings. In this chapter, we first elucidate the role of presence and immersion as requirements for eliciting emotional states in a virtual environment and discuss different VR methods for emotion induction. We then consider the organization of emotional states on a valence continuum (i.e., from negative to positive) and on this basis discuss the use of VR to study threat processing and avoidance as well as reward processing and approach behavior. Although the potential of VR has not been fully realized in laboratory and clinical settings yet, this technological tool can open up new avenues to better understand the neurobiological mechanisms of emotional responding in healthy and pathological conditions.

The relationship between sleep and appetitive conditioning: A systematic review and meta-analysis

This systematic review and meta-analysis (PROSPERO registration animal/human studies: CRD42021234793/CRD42021234790) examined the relationship between sleep and appetitive conditioning. Inclusion criteria included: a) appetitive conditioning paradigm; b) measure of conditioning; c) sleep measurement and/or sleep loss; d) human and/etor non-human animal samples; and e) written in English. Searches of seven databases returned 3777 publications. The final sample consisted of 42 studies using primarily animal samples and involving food- and drug-related conditioning tasks. We found sleep loss disrupted appetitive conditioning of food rewards (p < 0.001) but potentiated appetitive conditioning of drug rewards (p < 0.001). Furthermore, sleep loss negatively impacted extinction learning irrespective of the reward type. Post-learning sleep was associated with increases in REM sleep (p = 0.02). Findings suggest sleep loss potentiates the impact of psychoactive substances in a manner likely to produce an increased risk of problematic substance use. In obese/overweight populations, sleep loss may be associated with deficits in the conditioning and extinction of reward-related behaviours. Further research should assess the relationship between sleep and appetitive conditioning in humans.

Brain regulation of hunger and motivation: The case for integrating homeostatic and hedonic concepts and its implications for obesity and addiction

Obesity and other eating disorders are marked by dysregulations to brain metabolic, hedonic, motivational, and sensory systems that control food intake. Classic approaches in hunger research have distinguished between hedonic and homeostatic processes, and have mostly treated these systems as independent. Hindbrain structures and a complex network of interconnected hypothalamic nuclei control metabolic processes, energy expenditure, and food intake while mesocorticolimbic structures are though to control hedonic and motivational processes associated with food reward. However, it is becoming increasingly clear that hedonic and homeostatic brain systems do not function in isolation, but rather interact as part of a larger network that regulates food intake. Incentive theories of motivation provide a useful route to explore these interactions. Adapting incentive theories of motivation can enable researchers to better how motivational systems dysfunction during disease. Obesity and addiction are associated with profound alterations to both hedonic and homeostatic brain systems that result in maladaptive patterns of consumption. A subset of individuals with obesity may experience pathological cravings for food due to incentive sensitization of brain systems that generate excessive 'wanting' to eat. Further progress in understanding how the brain regulates hunger and appetite may depend on merging traditional hedonic and homeostatic concepts of food reward and motivation.

Behavioral response bias and event-related brain potentials implicate elevated incentive salience attribution to alcohol cues in emerging adults with lower sensitivity to alcohol

AIMS

This study used a behavioral approach-avoidance task including images of alcoholic beverages to test whether low sensitivity to alcohol (LS) is a phenotypical marker of a dispositional propensity to attribute bottom-up incentive value to naturally conditioned alcohol cues.

DESIGN, SETTING AND PARTICIPANTS

Experimental study with a measured individual difference variable at a university psychology laboratory in Missouri, MO, USA. Participants were 178 emerging adults (aged 18-20 years) varying in self-reported sensitivity to alcohol's acute effects.

MEASUREMENTS

Participants completed the alcohol approach-avoidance task while behavior (response time; RT) and the electroencephalogram (EEG) were recorded. Stimulus-locked event-related potentials (ERPs) provided indices of integrated (top-down and bottom-up) stimulus incentive value (P3 amplitude) and conflict between top-down task demands and bottom-up response propensities (N450 amplitude).

FINDINGS

Linear mixed models showed faster RT for 'alcohol-approach' relative to 'alcohol-avoid' trials for lower-sensitivity (LS) [mean_D  ± standard error_D (M_D  ± SE_D ) = 29.51 ± 9.74 ms, t₍₃₂₈₎  = 3.03, P = 0.003] but not higher-sensitivity (HS) individuals (M_D  ± SE_D  = 2.27 ± 9.33 ms, t₍₃₂₈₎  = 0.243, P = 0.808). There was enhanced N450 amplitude (response conflict) for alcohol-avoid relative to alcohol-approach trials for LS participants (M_D  ± SE_D  = 0.811 ± 0.198 μV, Z = 4.108, P < 0.001) and enhanced N450 amplitude for alcohol-approach relative to alcohol-avoid for HS participants (M_D  ± SE_D  = 0.419 ± 0.188 μV, Z = 2.235, P = 0.025). There was also enhanced P3 amplitude for alcohol-approach relative to alcohol-avoid for LS (M_D  ± SE_D  = 0.825 ± 0.204 μV, Z = 4.045, P < 0.001) but not HS (M_D  ± SE_D  = 0.013 ± 0.194 μV, Z = 0.068, P = 0.946).

CONCLUSIONS

Findings from a human laboratory study appear to support the notion that low sensitivity to alcohol indexes a propensity to attribute bottom-up incentive value to naturally conditioned alcohol cues.

From skinner box to daily life: Sign-tracker phenotype co-segregates with impulsivity, compulsivity, and addiction tendencies in humans

Pavlovian conditioning holds the potential to incentivize environmental cues, leading to approach behavior toward them, even outside our awareness. Animal models suggest that this is particularly true for the so-called sign-tracker (ST) phenotype, which is considered to reflect a predisposition toward developing addiction-related behaviours. Despite its potential clinical relevance, few studies have demonstrated the translational validity of this model, likely due to difficulties in studying Pavlovian processes in humans. To fill this gap, we combined an ecological momentary assessment with ambulatory peripheral autonomic monitoring to test the hypothesis that traits associated with ST in preclinical studies would be associated with attribution of high incentive salience to reward-related cues. Several times for 2 days, participants were asked to rate the attractiveness of several preselected ecological rewards (e.g., coffee) and the preceding cues (the smell of coffee) while their electrocardiogram was recorded. While no absolute difference in subjective and physiological measures of motivational approach to daily cues compared with rewards emerged, individuals with high levels of impulsivity, obsessive-compulsive, and addiction-prone behaviors rated as more attractive and showed a greater increase in sympathetic arousal to cues versus rewards. The opposite pattern emerged for those with low levels in those dispositional traits, who responded more (both subjectively and physiologically) to rewards compared with their preceding cues. This study represents an attempt to answer the call to parcel complex behaviors into smaller constructs, improving the early detection of those who are vulnerable to develop psychopathological disorders, particularly in the domain of impulse control such as addiction.

Deconstructing and reconstructing behaviour relevant to mental health disorders: The benefits of a psychological approach, with a focus on addiction

RUTHERFORD, L.G. and Milton, A.L. Deconstructing and reconstructing behaviour relevant to mental health disorders: what can psychology offer? NEUROSCI BIOBEHAV REV XX(X)XXX-XXX, 2021. - Current treatments for mental health disorders are successful only for some patients, and there is an unmet clinical need for new treatment development. One challenge for treatment development has been how best to model complex human conditions in animals, where mechanism can be more readily studied with a range of neuroscientific techniques. We suggest that an approach to modelling based on associative animal learning theory provides a good framework for deconstructing complex mental health disorders such that they can be studied in animals. These individual simple models can subsequently be used in combination to 'reconstruct' a more complex model of the mental health disorder of interest. Using examples primarily from the field of drug addiction, we explore the 'psychological approach' and suggest that in addition to facilitating translation and backtranslation of tasks between animal models and patients, it is also highly concordant with the concept of triangulation.

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.

Transfer of incentive salience from a first-order alcohol cue to a novel second-order alcohol cue among individuals at risk for alcohol use disorder: electrophysiological evidence

BACKGROUND AND AIMS

In susceptible individuals, cues associated with drug use are theorized to take on incentive-motivational properties, including the ability to reinforce higher-order, drug-related associative learning. This study aimed to test this prediction among people varying in risk for alcohol use disorder.

DESIGN, SETTING AND PARTICIPANTS

Repeated-measures experiment with a measured individual difference variable at a University psychology laboratory in Missouri, USA. One hundred and six young adults (96 contributed complete data) were pre-selected to represent the upper and lower quartiles of self-reported sensitivity to alcohol's acute effects.

MEASUREMENTS

Participants completed a second-order Pavlovian conditioning paradigm in which an initially neutral visual cue (second-order conditional stimulus; CS2 ) predicted onset of an olfactory cue (first-order conditional stimulus; CS1 ). Olfactory cues were isolated from alcoholic beverages, sweets and non-comestible substances, each presumed to have a natural history of first-order conditioning. Event-related potential responses to the CS2 across its conditioning and extinction, and to the CS1 , provided neurophysiological indices of incentive salience (IS).

FINDINGS

The IS of the alcohol CS1 was higher among participants low in alcohol sensitivity (LS), relative to their higher-sensitivity (HS) peers. The IS of the CS2 paired with the alcohol CS1 increased across the CS2 conditioning phase among LS but not HS participants. Also, LS (but not HS) individuals also experienced increases in alcohol craving following alcohol CS1 exposure, and this change was correlated with increases in the IS of the CS2 paired with the alcohol CS1 .

CONCLUSIONS

Alcoholic beverage odor, a proximal cue for alcohol consumption, appears to reinforce conditioning of neurophysiological responses to a novel cue among low alcohol sensitivity (LS) individuals but not high alcohol sensitivity individuals, providing the first evidence that the LS phenotype may be associated with differences in the conditioned reinforcing properties of alcohol-related cues. These findings support the idea that the LS phenotype may increase alcohol use disorder risk via susceptibility to incentive salience sensitization.

Helpless against food cues: the influence of pro- and anti-sugar videos on instrumental food-seeking behaviour in a Pavlovian-to-instrumental transfer paradigm

OBJECTIVE

External food cues can trigger food seeking by means of associative Stimulus-Outcome-Response learning mechanisms. These mechanisms can contribute to cued overeating. The present study aims at investigating if (cued) food-seeking behaviour can be influenced by pro- and anti-sugar videos.

DESIGN

Participants (N = 81) completed a Pavlovian-to-instrumental transfer (PIT) task: in an instrumental training, they learned associations between button presses and resulting sugary or sugar-free snacks. In a subsequent Pavlovian training, the snacks were paired with different cues. During the following transfer test, participants performed free button presses to win snacks while the cues were present or not.

MAIN OUTCOME MEASURES

The number of button presses for the different snacks in the transfer test was analysed.

RESULTS

We observed an outcome specific PIT effect, i.e. higher response rates for cued snacks. The videos did not affect the PIT effect. However, exploratory analyses revealed that the anti-sugar video led to fewer button presses for sugary snacks (compared to the pro-sugar video).

CONCLUSION

While snack-seeking behaviour was unaffected by the video's messages in the presence of food cues, in the absence of food cues there was evidence for a reduction of sugary snack choices by the anti-sugar video.

Avoidance in Anorexia Nervosa: Towards a research agenda

Anorexia Nervosa is a severe and disabling mental disorder and a huge challenge to treat. Intense fears of e.g., food, eating, weight gain and social evaluation are core features of anorexia nervosa and obstacles during treatment. The perceived threats trigger avoidance and safety behaviors like highly restrictive eating, strict eating rules, vomiting and body checking, to minimize feared outcomes. The role of avoidance in anorexia nervosa is however hardly studied experimentally. In the present article, the focus is on a new transdiagnostic research agenda featuring both basic and clinical experimental research into avoidance as a most important mechanism maintaining the eating disorder. Avoidance learning and the generalization of learned avoidance behaviors are discussed, as well as safety behaviors and the need for inhibitory learning as a treatment target during exposure therapy.

Love at first taste: Activation in reward-related brain regions during single-trial naturalistic appetitive conditioning in humans

Palatable food can trigger appetitive responses, such as salivation and approach tendencies. Though evolutionarily functional, these conditioned responses can encourage overeating and obesity when food is abundant. The current study examines the neural correlates of 'denovo' Pavlovian appetitive conditioning, pairing one class of unknown objects (conditioned stimuli, CS) with their sweet taste (unconditioned stimulus, US) during a single trial. To do so, 23 participants consumed unknown (marzipan) objects of one particular color (CS+) while only interacting with control stimuli of different color and shape (CS-). After this single-trial conditioning procedure, participants viewed and rated images of the marzipan figures and the control objects during functional magnetic resonance imaging (fMRI). Relative to the CS-, the CS+ elicited stronger activation in the dorsal striatum, a brain region associated with cue-reward coupling. Furthermore, conditioning effects in subjective 'craving', defined as increased palatability and desire to eat, were observed, and these were positively related to conditioning effects in the amygdala, a brain region associated with the need-dependent value of a reward. Thus, the study identified reward-related brain regions involved in single-trial appetitive learning, thereby providing a potential mechanism that contributes to the etiology of food craving. These findings might help to understand clinically relevant food cravings in individuals with eating or weight related concerns and might support the development of extinction based treatments.

From sign-tracking to attentional bias: Implications for gambling and substance use disorders

Sign-tracking behavior in Pavlovian autoshaping is known to be a relevant index of the incentive salience attributed to reward-related cues. Evidence has accumulated to suggest that animals that exhibit a sign-tracker phenotype are especially vulnerable to addiction and relapse due to their proneness to attribute incentive salience to drug cues, and their relatively weak cognitive and attentional control over their behavior. Interestingly, sign-tracking is also influenced by reward uncertainty in a way that may promote gambling disorder. Research indicates that reward uncertainty sensitizes sign-tracking responses and favors the development of a sign-tracker phenotype, compatible with the conditioned attractiveness of lights and sounds in casinos for problem gamblers. The study of attentional biases in humans (an effect akin to sign-tracking in animals) leads to similar observations, notably that the propensity to develop attraction for conditioned stimuli (CSs) is predictive of addictive behavior. Here we review the literature on drug addiction and gambling disorder, highlighting the similarities between studies of sign-tracking and attentional biases.

Mapping sign-tracking and goal-tracking onto human behaviors

As evidenced through classic Pavlovian learning mechanisms, environmental cues can become incentivized and influence behavior. These stimulus-outcome associations are relevant in everyday life but may be particularly important for the development of impulse control disorders including addiction. Rodent studies have elucidated specific learning profiles termed 'sign-tracking' and 'goal-tracking' which map onto individual differences in impulsivity and other behaviors associated with impulse control disorders' etiology, course, and relapse. Whereas goal-trackers are biased toward the outcome, sign-trackers fixate on features that are associated with but not necessary for achieving an outcome; a pattern of behavior that often leads to escalation of reward-seeking that can be maladaptive. The vast majority of the sign- and goal-tracking research has been conducted using rodent models and very few have bridged this concept into the domain of human behavior. In this review, we discuss the attributes of sign- and goal-tracking profiles, how these are manifested neurobiologically, and how these distinct learning styles could be an important tool for clinical interventions in human addiction.

Evidence for incentive salience sensitization as a pathway to alcohol use disorder

The incentive salience sensitization (ISS) theory of addiction holds that addictive behavior stems from the ability of drugs to progressively sensitize the brain circuitry that mediates attribution of incentive salience (IS) to reward-predictive cues and its behavioral manifestations. In this article, we establish the plausibility of ISS as an etiological pathway to alcohol use disorder (AUD). We provide a comprehensive and critical review of evidence for: (1) the ability of alcohol to sensitize the brain circuitry of IS attribution and expression; and (2) attribution of IS to alcohol-predictive cues and its sensitization in humans and non-human animals. We point out gaps in the literature and how these might be addressed. We also highlight how individuals with different alcohol subjective response phenotypes may differ in susceptibility to ISS as a pathway to AUD. Finally, we discuss important implications of this neuropsychological mechanism in AUD for psychological and pharmacological interventions attempting to attenuate alcohol craving and cue reactivity.

Skin Conductance Responses Indicate Children are Physiologically Aroused by Their Favourite Branded Food and Drink Products

Children's favourite food and beverage brands use various tactics to foster positive associations and loyalty. This brand-consumer dynamic is frequently influenced by the use of implicit techniques and emotional appeals. Few studies have used physiological methods to examine the connections that brands build with children and the influence this has on their automatic responses. These techniques are potentially less prone to bias than behavioural or cognitive methods. This is the first study to explore the implicit response that children have to images of their favourite food and beverage brands using skin conductance responses as a marker of arousal. Australian children aged 8-11 years (n = 48) were recruited. Images of the participants' favourite branded food and beverage products, alongside images of the same products unpackaged, their family and friends, and neutral objects were presented in a randomised order with a standard timed interval between images. Children were significantly more aroused by branded images of their favourite food and beverage products than by their unpackaged counterparts (p < 0.042, d = 0.4). The physiological response to the branded products was similar to the response to the children's family and friends (p = 0.900, d = -0.02). These findings suggest that children may have an implicit connection to their favourite branded products.

Pupil dilation as an implicit measure of appetitive Pavlovian learning

Appetitive Pavlovian conditioning is a learning mechanism of fundamental biological and pathophysiological significance. Nonetheless, its exploration in humans remains sparse, which is partly attributed to the lack of an established psychophysiological parameter that aptly represents conditioned responding. This study evaluated pupil diameter and other ocular response measures (gaze dwelling time, blink duration and count) as indices of conditioning. Additionally, a learning model was used to infer participants' learning progress on the basis of their pupil dilation. Twenty-nine healthy volunteers completed an appetitive differential delay conditioning paradigm with a primary reward, while the ocular response measures along with other psychophysiological (heart rate, electrodermal activity, postauricular and eyeblink reflex) and behavioral (ratings, contingency awareness) parameters were obtained to examine the relation among different measures. A significantly stronger increase in pupil diameter, longer gaze duration and shorter eyeblink duration was observed in response to the reward-predicting cue compared to the control cue. The Pearce-Hall attention model best predicted the trial-by-trial pupil diameter. This conditioned response was corroborated by a pronounced heart rate deceleration to the reward-predicting cue, while no conditioning effect was observed in the electrodermal activity or startle responses. There was no discernible correlation between the psychophysiological response measures. These results highlight the potential value of ocular response measures as sensitive indices for representing appetitive conditioning.

Opposing roles for amygdala and vmPFC in the return of appetitive conditioned responses in humans

Learning accounts of addiction and obesity emphasize the persistent power of Pavlovian reward cues to trigger craving and increase relapse risk. While extinction can reduce conditioned responding, Pavlovian relapse phenomena-the return of conditioned responding following successful extinction-challenge the long-term success of extinction-based treatments. Translational laboratory models of Pavlovian relapse could therefore represent a valuable tool to investigate the mechanisms mediating relapse, although so far human research has mostly focused on return of fear phenomena. To this end we developed an appetitive conditioning paradigm with liquid food rewards in combination with a 3-day design to investigate the return of appetitive Pavlovian responses and the involved neural structures in healthy subjects. Pavlovian conditioning (day 1) was assessed in 62 participants, and a subsample (n = 33) further completed extinction (day 2) and a reinstatement test (day 3). Conditioned responding was assessed on explicit (pleasantness ratings) and implicit measures (reaction time, skin conductance, heart rate, startle response) and reinstatement effects were further evaluated using fMRI. We observed a return of conditioned responding during the reinstatement test, evident by enhanced skin conductance responses, accompanied by enhanced BOLD responses in the amygdala. On an individual level, psychophysiological reinstatement intensity was significantly anticorrelated with ventromedial prefrontal cortex (vmPFC) activation, and marginally anticorrelated with enhanced amygdala-vmPFC connectivity during late reinstatement. Our results extend evidence from return of fear phenomena to the appetitive domain, and highlight the role of the vmPFC and its functional connection with the amygdala in regulating appetitive Pavlovian relapse.

Food-Pics_Extended-An Image Database for Experimental Research on Eating and Appetite: Additional Images, Normative Ratings and an Updated Review

Our current environment is characterized by the omnipresence of food cues. The taste and smell of real foods—but also graphical depictions of appetizing foods—can guide our eating behavior, for example, by eliciting food craving and anticipatory cephalic phase responses. To facilitate research into this so-called cue reactivity, several groups have compiled standardized food image sets. Yet, selecting the best subset of images for a specific research question can be difficult as images and image sets vary along several dimensions. In the present report, we review the strengths and weaknesses of popular food image sets to guide researchers during stimulus selection. Furthermore, we present a recent extension of our previously published database food-pics, which comprises an additional 328 food images from different countries to increase cross-cultural applicability. This food-pics_extended stimulus database, thus, encompasses and replaces food-pics. Normative data from a predominantly German-speaking sample are again presented as well as updated calculations of image characteristics.