Distinct spatiotemporal brainstem pathways of outcome valence during reward- and punishment-based learning.

Learning to seek rewards and avoid punishments, based on positive and negative choice outcomes, is essential for human survival. Yet, the neural underpinnings of outcome valence in the human brainstem and the extent to which they differ in reward and punishment learning contexts remain largely elusive. Here, using simultaneously acquired electroencephalography and functional magnetic resonance imaging data, we show that during reward learning the substantia nigra (SN)/ventral tegmental area (VTA) and locus coeruleus are initially activated following negative outcomes, while the VTA subsequently re-engages exhibiting greater responses for positive than negative outcomes, consistent with an early arousal/avoidance response and a later value-updating process, respectively. During punishment learning, we show that distinct raphe nucleus and SN subregions are activated only by negative outcomes with a sustained post-outcome activity across time, supporting the involvement of these brainstem subregions in avoidance behavior. Finally, we demonstrate that the coupling of these brainstem structures with other subcortical and cortical areas helps to shape participants' serial choice behavior in each context.

Psychopathic traits and reinforcement learning under acute stress.

OBJECTIVE: Individuals with high levels of psychopathic traits are often characterized by aberrant reinforcement learning. This type of learning, which implicates making choices that maximize rewards and minimize punishments, may be affected by acute stress. However, how acute stress affects reinforcement learning in individuals with different levels of psychopathic traits is not well-understood. Here, we investigated whether and how individual differences in psychopathic traits modulated the impact of acute stress on reward and punishment learning. METHOD: Sixty-two male participants from a university sample completed the Self-Report Psychopathy-Short Form scale and performed a reinforcement-learning task involving monetary gains and losses whilst under acute stress and control conditions. RESULTS: Individual differences in psychopathic traits modulated the impact of acute stress on behavioral performance toward obtaining gains, but not toward avoiding losses. As levels of psychopathic traits increased, the impairing effect of acute stress on reward learning decreased. Specifically, acute stress impaired performance toward seeking gains to a larger extent in individuals with lower levels of psychopathic traits than in individuals with higher levels of these traits. CONCLUSIONS: Our study indicates that psychopathic traits modulate the impact of acute stress on reward learning.

Acute stress blunts prediction error signals in the dorsal striatum during reinforcement learning.

Acute stress is pervasive in everyday modern life and is thought to affect how people make choices and learn from them. Reinforcement learning, which implicates learning from the unexpected rewarding and punishing outcomes of our choices (i.e., prediction errors), is critical for adjusted behaviour and seems to be affected by acute stress. However, the neural mechanisms by which acute stress disrupts this type of learning are still poorly understood. Here, we investigate whether and how acute stress blunts neural signalling of prediction errors during reinforcement learning using model-based functional magnetic resonance imaging. Male participants completed a well-established reinforcement-learning task involving monetary gains and losses whilst under stress and control conditions. Acute stress impaired participants' (n = 23) behavioural performance towards obtaining monetary gains (p < 0.001), but not towards avoiding losses (p = 0.57). Importantly, acute stress blunted signalling of prediction errors during gain and loss trials in the dorsal striatum (p = 0.040) - with subsidiary analyses suggesting that acute stress preferentially blunted signalling of positive prediction errors. Our results thus reveal a neurocomputational mechanism by which acute stress may impair reward learning.

Acute stress impairs reward learning in men.

Acute stress is ubiquitous in everyday life, but the extent to which acute stress affects how people learn from the outcomes of their choices is still poorly understood. Here, we investigate how acute stress impacts reward and punishment learning in men using a reinforcement-learning task. Sixty-two male participants performed the task whilst under stress and control conditions. We observed that acute stress impaired participants' choice performance towards monetary gains, but not losses. To unravel the mechanism(s) underlying such impairment, we fitted a reinforcement-learning model to participants' trial-by-trial choices. Computational modeling indicated that under acute stress participants learned more slowly from positive prediction errors - when the outcomes were better than expected - consistent with stress-induced dopamine disruptions. Such mechanistic understanding of how acute stress impairs reward learning is particularly important given the pervasiveness of stress in our daily life and the impact that stress can have on our wellbeing and mental health.

Helping behavior in rats (Rattus norvegicus) when an escape alternative is present.

Prosocial behavior in rats is known to occur in response to a familiar rat's distress, but the motivations underlying prosocial behavior remain elusive. In this study, we adapted the experimental setting of Ben-Ami Bartal, Decety, and Mason (2011) to explore different motivations behind helping behavior in adolescent rats. In the original setting, a free rat is placed in an arena where a cagemate is trapped inside a restrainer that can only be opened from the outside by the free rat. Here we added a dark compartment to the experimental setting that allowed the free rat to escape the arena and the distress evoked by the trapped cagemate, based on rodents' aversion to bright areas. As a control, we tested rats in the same arena but with the door to the dark area closed. Our results showed that all free rats, except one in the escape condition, learned to open the restrainer's door. However, in the escape condition, rats took significantly longer to open the restrainer to the cagemates when compared with rats that could not escape. To further explore the motivations underlying these group differences in door-opening latencies, we measured both rats' behavior. We found that struggling behavior (i.e., distress) in the trapped rat did not affect door-opening, whereas exploratory behavior (i.e., proactive/positive behavior) in both rats contributed to shorter times. Our results highlight that adolescent rats show prosocial behavior even when they can escape without helping and contribute to demonstrate the role of positive emotional states in prosocial behavior. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Fatal hepatitis B reactivation treated with entecavir in an isolated anti-HBs positive lymphoma patient: a case report and literature review.

Hepatitis B virus (HBV) reactivation is a well-recognized complication that occurs in lymphoma patients who undergo chemotherapy. Only very few cases of HBV reactivation in patients with isolated antibody against hepatitis B surface antigen (anti-HBs) have been reported. We present a case of a 78-year-old woman diagnosed with diffuse large B cell non-Hodgkin's lymphoma who only displayed a positive anti-HBs, as the single possible marker of occult HBV infection, before starting therapy. She was treated with several chemotherapeutic regimens (including rituximab) for disease relapses during 3 years. Forty days after the last cycle of chemotherapy, she presented with jaundice, markedly elevated serum aminotransferase levels, and coagulopathy. HBV serology showed positivity for HBsAg, anti-HBc and anti-HBs. HBV DNA was positive. Antiviral treatment with entecavir was promptly initiated, but the patient died from liver failure. A review of the literature of HBV reactivation in patients with detectable anti-HBs levels is discussed.