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PubMed2026

Effects of acute inflammatory challenge on anhedonia and social reward processing: A randomized controlled trial of endotoxin.

Anhedonia is a core feature of depression that reflects reward system dysfunction. Acute inflammatory challenge has been shown to induce transient anhedonia and reward processing deficits, but its effects on distinct components of social reward processes remain poorly understood. This randomized, double-blind, placebo-controlled study evaluated anhedonia and social reward responsivity following acute inflammatory challenge. Low-dose endotoxin (0.8 ng/kg body weight; n = 18) or placebo (same volume of 0.9% saline; n = 22) was administered to female adults (ages 25-44). Anhedonia (Snaith-Hamilton Pleasure Questionnaire) and blood samples for cytokine assessment were collected pre-infusion and 2 and 4 h post-infusion. Social reward motivation (wanting to engage in a social task) was assessed at a baseline eligibility visit and 2 h post-infusion. Sensitivity to positive social cues (attentional bias toward and recognition of happy faces) was assessed pre-infusion and 2 h post-infusion. Results showed that endotoxin increased anhedonic symptoms (p = .005) and decreased social motivation by 2 h post-infusion (p = .001); within the endotoxin condition, changes in both outcomes were associated with increases in TNF-α (p's < .04). A significant condition-by-time interaction for happy-face recognition (p = .011) was driven by increased accuracy in the placebo (p = .04) but not endotoxin (p = .43) condition. Endotoxin administration did not affect attentional bias toward happy faces. Findings suggest that acute inflammatory challenge induces anhedonia and reduces social motivation, with more limited effects on sensitivity to positive social cues, highlighting specific reward-related pathways through which immune activation may contribute to inflammation-associated depression. Future work could examine whether immune-related changes in social motivation contribute to motivational deficits in depression.

Humans↗

PubMed2026

Post-weaning social isolation increases reward-seeking behavior in mice.

Social isolation is a growing public health concern. Although isolation at any age is harmful, previous studies have shown that isolation during adolescence, correlating with critical periods of brain development, can impair cognitive function and increase the risk for psychiatric illness later in life. In this study, we utilized a mouse model of social isolation (SI) during adolescence (postnatal day 21-35) and compared performance of isolated and group-housed mice on a touchscreen-based continuous performance test (rCPT) and fixed ratio/progressive ratio (FR/PR) tasks in adulthood. SI improved performance in the rCPT and the improvement in performance was consistent across time bins within the 45-minute testing session. There were no effects of SI on reaction times or reward retrieval latencies. A possible confound for performance in the rCPT would be SI-induced changes in reward-seeking or motivation for the strawberry milk reward. We next compared the SI mice to their group-housed littermate controls on both PR and FR schedules of reinforcement and found that SI mice had higher breakpoints on a PR4 schedule and earned significantly more reinforcers on an FR1 schedule of reinforcement compared to their group-housed littermates, suggesting that high performance in the CPT may be due to increased motivation for food rewards. These data indicate that SI during adolescence has significant effects on reward-seeking behavior in adult mice and may provide a useful behavioral model for studying the link between SI and risk for neuropsychiatric disorders.

Animals↗

PubMed2026

Brain network alterations underlying cue reactivity and craving in abstinent methamphetamine users: a systematic review of functional MRI findings.

BACKGROUND: Methamphetamine use disorder (MUD) is marked by intense craving and high relapse risk, often triggered by drug-related cues. Functional magnetic resonance imaging (fMRI) provides key insight into the neural basis of this cue reactivity, implicating large-scale brain networks for reward, motivation, and control. Yet, findings remain inconsistent across studies due to differences in task design, abstinence duration, and participant characteristics. OBJECTIVE: This systematic review synthesises evidence on how abstinence influences brain network alterations underlying cue reactivity and craving in methamphetamine users, integrating task-based and resting-state fMRI findings within leading neurobiological models of addiction. METHODS: A systematic search of PubMed, Scopus, Web of Science, and Ovid was conducted up to August 10, 2025, following PRISMA 2020 guidelines. Eligible fMRI studies examined cue reactivity or craving in abstinent methamphetamine users. Data were extracted on activation, connectivity, and brain-behaviour associations, and synthesised narratively. RESULTS: Task-based studies revealed heightened activation across reward, salience, and control networks during cue exposure, which diminished as parietal and executive control systems re-engaged with longer abstinence. Resting-state findings showed disrupted intrinsic connectivity among default mode, salience, and frontoparietal networks, reflecting persistent imbalances linked to craving and use severity. CONCLUSION: fMRI evidence shows that MUD is marked by network-level disruption linking reward, salience, and control systems. Task-based findings reveal strong cue reactivity in reward circuits, while resting-state data show persistent imbalance among default mode and control networks. With abstinence, partial restoration of network integrity emerges, highlighting both vulnerability and opportunities for targeted, recovery-based interventions.

Humans↗

PubMed2026

The effect of tDCS on emotion-related risk-taking behavior and delay discounting in adults with ADHD.

INTRODUCTION: Adults with Attention Deficit Hyperactivity Disorder (ADHD) often engage in risky behaviors due to impaired decision-making processes. This study aims to investigate the effects of transcranial direct current stimulation (tDCS) over the dorsolateral prefrontal cortex (dlPFC) and ventromedial prefrontal cortex (vmPFC) on emotion-related risk-taking behavior and delay discounting in adults with ADHD. METHODS: Thirty adults with ADHD underwent three tDCS conditions, administered in a randomized order with at least one week between sessions: (1) left dlPFC anode/right vmPFC cathode, (2) left dlPFC cathode/right vmPFC anode, and (3) sham stimulation. In each session, participants completed the Delay Discounting Task (DDT) and the Modified Balloon Analogue Risk Task (mBART) under three emotional conditions (neutral, positive, and negative) which were induced using emotionally congruent photographs and sounds. Galvanic skin responses (GSR) were also recorded. In the DDT, both area under the curve (AUC) values and log-transformed discounting rates (log k) were calculated for small, medium, and large reward magnitudes (RM). Exploratory electric field modeling was also performed to characterize current distribution. RESULTS: The findings demonstrated task-specific effects of tDCS on decision-making. Although no overall tDCS effect was observed on DDT performance, significant tDCS × RM interactions emerged, particularly for smaller rewards. In contrast, exploratory analyses suggested that tDCS affected all mBART scores. Emotional condition did not influence consistently behavioral performance in either task, whereas both emotional stimulation and tDCS significantly affected GSR responses. However, exploratory electric field modeling indicated a broad prefrontal current distribution extending beyond the intended cortical targets. CONCLUSIONS: These findings suggest preliminary evidence that prefrontal tDCS can influence risk-related decision-making and autonomic responses in adults with ADHD. However, its effects on delay discounting appear to be context-dependent and limited to specific RMs. Future studies combining neuroimaging with individualized electric field modeling are needed to clarify the neural mechanisms underlying the observed effects of tDCS and to optimize stimulation protocols in adults with ADHD.

Humans↗