Fear conditioning and extinction in alcohol dependence: Evidence for abnormal amygdala reactivity

Emotional processing in binge drinking, tobacco use disorder and their comorbidity in youth: A preregistered PRISMA scoping review

BACKGROUND

Binge drinking (BD) and tobacco use disorder (TUD) are prevalent among youth, with significant social and health implications. However, research into the emotional impairments associated with BD and TUD during adolescence is sparse and lacks integration within a comprehensive model of emotional processes. Moreover, the impact of comorbid BD and TUD on emotional deficits remains largely unexplored. We propose the first review focused on the variation of emotional deficits in BD, TUD, or their comorbidity among adolescents and we systematically explore differences across various emotional abilities.

METHODS

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews guidelines (PRISMA-ScR), we conducted a preregistered review of existing literature on emotional processing impairments in BD and/or TUD among adolescents. From 481 papers initially identified, 7 were included in this review. Additionally, we proposed experimental avenues for future research based on identified shortcomings in current literature.

RESULTS

Our scoping review indicates that emotional deficits are likely prevalent in both BD and TUD populations, affecting emotional appraisal/identification, response, and regulation. However, further investigation is necessary to ascertain the magnitude and scope of these deficits in adolescents and adults, as well as to delineate the distinct or combined influence of BD and TUD on emotional disturbances.

CONCLUSION

While some emotional deficits are apparent, we contend that examining emotional deficits in BD and TUD separately, as well as together, would offer a more comprehensive understanding of their nature and inform the development of novel treatment strategies.

Renewal in human fear conditioning: A systematic review and meta-analysis

Renewal is a 'return of fear' manipulation in human fear conditioning to investigate learning processes underlying anxiety and trauma. Even though renewal paradigms are widely used, no study has compared the strength of different renewal paradigms. We conduct a systematic review (N = 80) and meta-analysis (N = 23) of human fear conditioning studies assessing renewal. Our analysis shows that the classic ABA design is the most effective paradigm, compared to ABC and ABBA designs. We present evidence that conducting extinction in multiple contexts and increasing the similarity between acquisition and extinction contexts reduce renewal. Furthermore, we show that additional cues can be used as safety and 'protection from extinction' cues. The review shows that alcohol weakens the extinction process and that older adults appear less sensitive to context changes and thus show less renewal. The large variability in approaches to study renewal in humans suggests that standardisation of fear conditioning procedures across laboratories would be of great benefit to the field.

Effects of chronic haloperidol treatment on the expression of fear memory and fear memory extinction in the cued fear-conditioned rats

AIM

Impairments in emotional memory are frequently observed in several mental disorders, highlighting their significance as potential therapeutic targets. Recent research on the cued fear conditioning model has elucidated the neural circuits involved in fear memory processing. However, contradictory findings have been reported concerning the role of dopamine and the impact of dopamine D2 receptor (D2R) antagonists. There is notably limited knowledge regarding the clinical utility of chronic D2R antagonist treatments. This study aimed to uncover how such treatments affect fear memory processing.

METHODS

We utilized a cued fear conditioning rat model and conducted chronic haloperidol treatment for 14 days. Subsequently, to investigate the effect of chronic haloperidol treatment on fear-conditioned memory expression and extinction, we observed freezing behavior under exposure to a conditioned stimulus for 14 days.

RESULTS

Chronic haloperidol treatment suppressed freezing time on the fear memory expression. In contrast, a single haloperidol administration enhanced the freezing time on fear memory expression and delayed extinction.

CONCLUSION

The results of this study suggest that chronic administration of antipsychotic drugs affects fear memory processing differently from single-dose administration. This indicates that the effects of chronic D2R antagonist treatment are distinct from the nonspecific effects of the drugs. This study provides fundamental insights that may contribute to our understanding of therapeutic mechanisms for fear memory disorders related to D2R in the future.

Elevated Amygdala Responses During De Novo Pavlovian Conditioning in Alcohol Use Disorder Are Associated With Pavlovian-to-Instrumental Transfer and Relapse Latency

Background

Contemporary learning theories of drug addiction ascribe a key role to Pavlovian learning mechanisms in the development, maintenance, and relapse of addiction. In fact, cue-reactivity research has demonstrated the power of alcohol-associated cues to activate the brain's reward system, which has been linked to craving and subsequent relapse. However, whether de novo Pavlovian conditioning is altered in alcohol use disorder (AUD) has rarely been investigated.

Methods

To characterize de novo Pavlovian conditioning in AUD, 62 detoxified patients with AUD and 63 matched healthy control participants completed a Pavlovian learning task as part of a Pavlovian-to-instrumental transfer paradigm during a functional magnetic resonance imaging session. Patients were followed up for 12 months to assess drinking behavior and relapse status.

Results

While patients and healthy controls did not differ in their ability to explicitly acquire the contingencies between conditioned and unconditioned stimuli, patients with AUD displayed significantly stronger amygdala responses toward Pavlovian cues, an effect primarily driven by stronger blood oxygen level-dependent differentiation during learning from reward compared with punishment. Moreover, in patients compared with controls, differential amygdala responses during conditioning were positively related to the ability of Pavlovian stimuli to influence ongoing instrumental choice behavior measured during a subsequent Pavlovian-to-instrumental transfer test. Finally, patients who relapsed within the 12-month follow-up period showed an inverse association between amygdala activity during conditioning and relapse latency.

Conclusions

We provide evidence of altered neural correlates of de novo Pavlovian conditioning in patients with AUD, especially for appetitive stimuli. Thus, heightened processing of Pavlovian cues might constitute a behaviorally relevant mechanism in alcohol addiction.

Learning from others' experience: Social fear conditioning deficits in patients with severe alcohol use disorder

BACKGROUND

Alcohol use disorder (AUD) is a significant public health problem. A better understanding of the psychosocial factors contributing to AUD is important for developing public health policy. The purpose of this study was to identify social mechanisms involved in AUD and, more specifically, to determine whether vicarious learning deficits are related to the disorder. A secondary objective was to evaluate the role of empathy in social fear conditioning.

METHODS

Patients with severe AUD (n = 30) and healthy participants (n = 30) performed a social fear learning (SFL) task. The task assesses how an association between a stimulus and an aversive consequence is acquired through social means. Specifically, participants observed a person receiving an electric shock (unconditioned stimulus; US) that was associated (conditioned stimulus; CS+) or not (CS-) with a neutral CS. The skin conductance response was used to measure the effect of learning.

RESULTS

Individuals with severe AUD showed a deficit in SFL, indicating that they had difficulty learning from another's negative experience. Patients also evaluated the emotional experience as less unpleasant than healthy participants.

CONCLUSIONS

This study is the first to show that patients with severe AUD have social learning deficits. The findings suggest that these individuals do not learn from another's negative experience. At a fundamental level, the findings demonstrate the importance of understanding the role of social mechanisms in AUD. At a clinical level, the study highlights the potential for using social learning enhancement to prevent relapse in individuals with severe AUD.

From safety to frustration: The neural substrates of inhibitory learning in aversive and appetitive conditioning procedures

Inhibitory associative learning counters the effects of excitatory learning, whether appetitively or aversively motivated. Moreover, the affective responses accompanying the inhibitory associations are of opponent valence to the excitatory conditioned responses. Inhibitors for negative aversive outcomes (e.g. shock) signal safety, while inhibitors for appetitive outcomes (e.g. food reward) elicit frustration and/or disappointment. This raises the question as to whether studies using appetitive and aversive conditioning procedures should demonstrate the same neural substrates for inhibitory learning. We review the neural substrates of appetitive and aversive inhibitory learning as measured in different procedural variants and in the context of the underpinning excitatory conditioning on which it depends. The mesocorticolimbic dopamine pathways, retrosplenial cortex and hippocampus are consistently implicated in inhibitory learning. Further neural substrates identified in some procedural variants may be related to the specific motivation of the learning task and modalities of the learning cues. Finally, we consider the translational implications of our understanding of the neural substrates of inhibitory learning, for obesity and addictions as well as for anxiety disorders.

Epigenome-wide association study of alcohol consumption in N = 8161 individuals and relevance to alcohol use disorder pathophysiology: identification of the cystine/glutamate transporter SLC7A11 as a top target

Alcohol misuse is common in many societies worldwide and is associated with extensive morbidity and mortality, often leading to alcohol use disorders (AUD) and alcohol-related end-organ damage. The underlying mechanisms contributing to the development of AUD are largely unknown; however, growing evidence suggests that alcohol consumption is strongly associated with alterations in DNA methylation. Identification of alcohol-associated methylomic variation might provide novel insights into pathophysiology and novel treatment targets for AUD. Here we performed the largest single-cohort epigenome-wide association study (EWAS) of alcohol consumption to date (N = 8161) and cross-validated findings in AUD populations with relevant endophenotypes, as well as alcohol-related animal models. Results showed 2504 CpGs significantly associated with alcohol consumption (Bonferroni p value < 6.8 × 10-8) with the five leading probes located in SLC7A11 (p = 7.75 × 10-108), JDP2 (p = 1.44 × 10-56), GAS5 (p = 2.71 × 10-47), TRA2B (p = 3.54 × 10-42), and SLC43A1 (p = 1.18 × 10-40). Genes annotated to associated CpG sites are implicated in liver and brain function, the cellular response to alcohol and alcohol-associated diseases, including hypertension and Alzheimer's disease. Two-sample Mendelian randomization confirmed the causal relationship of consumption on AUD risk (inverse variance weighted (IVW) p = 5.37 × 10-09). A methylation-based predictor of alcohol consumption was able to discriminate AUD cases in two independent cohorts (p = 6.32 × 10-38 and p = 5.41 × 10-14). The top EWAS probe cg06690548, located in the cystine/glutamate transporter SLC7A11, was replicated in an independent cohort of AUD and control participants (N = 615) and showed strong hypomethylation in AUD (p < 10-17). Decreased CpG methylation at this probe was consistently associated with clinical measures including increased heavy drinking days (p < 10-4), increased liver function enzymes (GGT (p = 1.03 × 10-21), ALT (p = 1.29 × 10-6), and AST (p = 1.97 × 10-8)) in individuals with AUD. Postmortem brain analyses documented increased SLC7A11 expression in the frontal cortex of individuals with AUD and animal models showed marked increased expression in liver, suggesting a mechanism by which alcohol leads to hypomethylation-induced overexpression of SLC7A11. Taken together, our EWAS discovery sample and subsequent validation of the top probe in AUD suggest a strong role of abnormal glutamate signaling mediated by methylomic variation in SLC7A11. Our data are intriguing given the prominent role of glutamate signaling in brain and liver and might provide an important target for therapeutic intervention.

Positive alcohol expectancy and resting-state functional connectivity of the insula in problem drinking

Positive alcohol expectancy (AE), a significant predictor of excessive alcohol consumption, is associated with heightened drinking motivation and reduced control. As the insula interacts with the limbic and prefrontal structures to integrate stimulus saliency, interoception, and cognitive control, the region may play a unique role in modulating AE. Here, we examined resting-state functional connectivity of the right and left insula in relation to AE in 180 adult drinkers. Whole-brain multiple regressions and path analysis were performed to delineate the inter-relationship between AE, insular connectivity, and drinking severity. We found that heightened AE was associated with diminished right insular connectivity with regions involved in negative emotion processing and self-control, including the amygdala, putamen, and ventromedial prefrontal cortex. In contrast, there was a positive relationship between AE and right insular connectivity with regions implicated in motivated responses to alcohol stimuli, including the superior parietal lobule, postcentral and superior frontal gyri. Path analysis showed that the two sets of right insular connectivity exhibited opposing associations with AE and that their net strength (i.e., "control minus motivation") was negatively correlated with AE and drinking severity. Analyses of the left insula seed, in contrast, did not yield regional connectivity in significant correlation with AE. These findings highlight the roles of right insula connectivity in motivational and regulatory processes that may differentially modulate drinking behavior. Recruitment of the motivational circuit and/or disengagement of the affective control circuit would be associated with heightened AE and heavier alcohol consumption.

Epigenome-wide association study and multi-tissue replication of individuals with alcohol use disorder: evidence for abnormal glucocorticoid signaling pathway gene regulation

Alcohol use disorder (AUD) is a chronic debilitating disorder with limited treatment options and poorly defined pathophysiology. There are substantial genetic and epigenetic components; however, the underlying mechanisms contributing to AUD remain largely unknown. We conducted the largest DNA methylation epigenome-wide association study (EWAS) analyses currently available for AUD (total N = 625) and employed a top hit replication (N = 4798) using a cross-tissue/cross-phenotypic approach with the goal of identifying novel epigenetic targets relevant to AUD. Results show that a network of differentially methylated regions in glucocorticoid signaling and inflammation-related genes were associated with alcohol use behaviors. A top probe consistently associated across all cohorts was located in the long non-coding RNA growth arrest specific five gene (GAS5) (p < 10-24). GAS5 has been implicated in regulating transcriptional activity of the glucocorticoid receptor and has multiple functions related to apoptosis, immune function and various cancers. Endophenotypic analyses using peripheral cortisol levels and neuroimaging paradigms showed that methylomic variation in GAS5 network-related probes were associated with stress phenotypes. Postmortem brain analyses documented increased GAS5 expression in the amygdala of individuals with AUD. Our data suggest that alcohol use is associated with differential methylation in the glucocorticoid system that might influence stress and inflammatory reactivity and subsequently risk for AUD.