Anthony J. Porcelli

Acute stress influences neural circuits of reward processing

People often make decisions under aversive conditions such as acute stress. Yet, less is known about the process in which acute stress can influence decision-making. A growing body of research has established that reward-related information associated with the outcomes of decisions exerts a powerful influence over the choices people make and that an extensive network of brain regions, prominently featuring the striatum, is involved in the processing of this reward-related information. Thus, an important step in research on the nature of acute stress’ influence over decision-making is to examine how it may modulate responses to rewards and punishments within reward-processing neural circuitry. In the current experiment, we employed a simple reward processing paradigm – where participants received monetary rewards and punishments – known to evoke robust striatal responses. Immediately prior to performing each of two task runs, participants were exposed to acute stress (i.e., cold pressor) or a no stress control procedure in a between-subjects fashion. No stress group participants exhibited a pattern of activity within the dorsal striatum and orbitofrontal cortex consistent with past research on outcome processing – specifically, differential responses for monetary rewards over punishments. In contrast, acute stress group participants’ dorsal striatum and orbitofrontal cortex demonstrated decreased sensitivity to monetary outcomes and a lack of differential activity. These findings provide insight into how neural circuits may process rewards and punishments associated with simple decisions under acutely stressful conditions.People often make decisions under aversive conditions such as acute stress. Yet, less is known about the process in which acute stress can influence decision-making. A growing body of research has established that reward-related information associated with the outcomes of decisions exerts a powerful influence over the choices people make and that an extensive network of brain regions, prominently featuring the striatum, is involved in the processing of this reward-related information. Thus, an important step in research on the nature of acute stress’ influence over decision-making is to examine how it may modulate responses to rewards and punishments within reward processing neural circuitry. In the current experiment, we employed a simple reward processing paradigm – where participants received monetary rewards and punishments – known to evoke robust striatal responses. Immediately prior to performing each of two task runs, participants were exposed to acute stress (i.e., cold pressor) or a no stress control procedure in a between-subjects fashion. No stress group participants exhibited a pattern of activity within the dorsal striatum and orbitofrontal cortex (OFC) consistent with past research on outcome processing – specifically, differential responses for monetary rewards over punishments. In contrast, acute stress group participants’ dorsal striatum and OFC demonstrated decreased sensitivity to monetary outcomes and a lack of differential activity. These findings provide insight into how neural circuits may process rewards and punishments associated with simple decisions under acutely stressful conditions.

The effects of acute stress on human prefrontal working memory systems

We examined the relationship between acute stress and prefrontal-cortex (PFC) based working memory (WM) systems using behavioral (Experiment 1) and functional magnetic resonance imaging (fMRI; Experiment 2) paradigms. Subjects performed a delayed-response item-recognition task, with alternating blocks of high and low WM demand trials. During scanning, participants performed this task under three stress conditions: cold stress (induced by cold-water hand-immersion), a room temperature water control (induced by tepid-water hand-immersion), and no-water control (no hand-immersion). Performance was affected by WM demand, but not stress. Cold stress elicited greater salivary cortisol readings in behavioral subjects, and greater PFC signal change in fMRI subjects, than control conditions. These results suggest that, under stress, increases in PFC activity may be necessary to mediate cognitive processes that maintain behavioral organization.

Individual differences in delay discounting under acute stress: the role of trait perceived stress.

Delay discounting refers to the reduction of the value of a future reward as the delay to that reward increases. The rate at which individuals discount future rewards varies as a function of both individual and contextual differences, and high delay discounting rates have been linked with problematic behaviors, including drug abuse and gambling. The current study investigated the effects of acute anticipatory stress on delay discounting, while considering two important factors: individual perceptions of stress and whether the stressful situation is future-focused or present-focused. Half of the participants experienced acute stress by anticipating giving a videotaped speech. This stress was either future-oriented (speech about future job) or present-oriented (speech about physical appearance). They then performed a delay discounting task, in which they chose between smaller, immediate rewards, and larger, delayed rewards. Their scores on the Perceived Stress Scale were also collected. The way in which one appraises stressful situations interacts with acute stress to influence choices; under stressful conditions, delay discounting rate was highest in individuals with low trait perceived stress and lowest for individuals with high trait perceived stress. This result might be related to individual variation in reward responsiveness under stress. Furthermore, the time orientation of the task interacted with its stressfulness to affect the individual’s propensity to choose immediate rewards. These findings add to our understanding of the intermediary factors between stress and decision-making.

The effects of acute stress exposure on striatal activity during Pavlovian conditioning with monetary gains and losses

Pavlovian conditioning involves the association of an inherently neutral stimulus with an appetitive or aversive outcome, such that the neutral stimulus itself acquires reinforcing properties. Across species, this type of learning has been shown to involve subcortical brain regions such as the striatum and the amygdala. It is less clear, however, how the neural circuitry involved in the acquisition of Pavlovian contingencies in humans, particularly in the striatum, is affected by acute stress. In the current study, we investigate the effect of acute stress exposure on Pavlovian conditioning using monetary reinforcers. Participants underwent a partial reinforcement conditioning procedure in which neutral stimuli were paired with high and low magnitude monetary gains and losses. A between-subjects design was used, such that half of the participants were exposed to cold stress while the remaining participants were exposed to a no stress control procedure. Cortisol measurements and subjective ratings were used as measures of stress. We observed an interaction between stress, valence, and magnitude in the ventral striatum, with the peak in the putamen. More specifically, the stress group exhibited an increased sensitivity to magnitude in the gain domain. This effect was driven by those participants who experienced a larger increase in circulating cortisol levels in response to the stress manipulation. Taken together, these results suggest that acute stress can lead to individual differences in circulating cortisol levels which influence the striatum during Pavlovian conditioning with monetary reinforcers.

Social closeness and feedback modulate susceptibility to the framing effect.

Although we often seek social feedback (SFB) from others to help us make decisions, little is known about how SFB affects decisions under risk, particularly from a close peer. We conducted two experiments using an established framing task to probe how decision-making is modulated by SFB valence (positive, negative) and the level of closeness with feedback provider (friend, confederate). Participants faced mathematically equivalent decisions framed as either an opportunity to keep (gain frame) or lose (loss frame) part of an initial endowment. Periodically, participants were provided with positive (e.g., “Nice!”) or negative (e.g., “Lame!”) feedback about their choices. Such feedback was provided by either a confederate (Experiment 1) or a gender-matched close friend (Experiment 2). As expected, the framing effect was observed in both experiments. Critically, an individuals susceptibility to the framing effect was modulated by the valence of the SFB, but only when the feedback provider was a close friend. This effect was reflected in the activation patterns of ventromedial prefrontal cortex and posterior cingulate cortex, regions involved in complex decision-making. Taken together, these results highlight social closeness as an important factor in understanding the impact of SFB on neural mechanisms of decision-making.

Visual working memory for global, object, and part-based information

We investigated visual working memory for novel objects and parts of novel objects. After a delay period, participants showed strikingly more accurate performance recognizing a single whole object than the parts of that object. This bias to remember whole objects, rather than parts, persisted even when the division between parts was clearly defined and the parts were disconnected from each other so that, in order to remember the single whole object, the participants needed to mentally combine the parts. In addition, the bias was confirmed when the parts were divided by color. These experiments indicated that holistic perceptual-grouping biases are automatically used to organize storage in visual working memory. In addition, our results suggested that the bias was impervious to top-down consciously directed control, because when task demands were manipulated through instruction and catch trials, the participants still recognized whole objects more quickly and more accurately than their parts. This bias persisted even when the whole objects were novel and the parts were familiar. We propose that visual working memory representations depend primarily on the global configural properties of whole objects, rather than part-based representations, even when the parts themselves can be clearly perceived as individual objects. This global configural bias beneficially reduces memory load on a capacity-limited system operating in a complex visual environment, because fewer distinct items must be remembered.

Reward Processing in the Human Brain: Insights from fMRI

Publisher Summary Reward processing engages diverse brain regions, including multiple prefrontal regions and the basal ganglia (particularly the multifaceted striatum). Corticostriatal circuits are involved in computation of subjective value for experienced rewards, leading to a valuation signal that can be used to guide future decisions via reinforcement-learning mechanisms. In recent years, an explosion of neuroimaging research has replicated and extended findings from a rich body of animal literature on basic brain reward systems to probe how such systems are modulated by more complex processes that typically influence goal-directed behavior in human society. The goal of this chapter is to discuss the integration of neuroimaging studies of reward processing, with emphasis on cortical-striatal circuits involved in goal-directed behavior and the valuation of reward-related information. Neuroimaging research highlights functional subdivisions within components of this corticostriatal circuitry. Reward processing can be modulated by a number of additional factors, including magnitude of reward, risk, time, and social context. Furthermore, the chapter highlights how cortical-striatal circuits and valuation signals can be modulated by the presence of more complex factors such as risk, time, and social context. Important directions for future research include the study of the complex modulation of reward processing by social factors, as well as processing of aversive information that can also modulate behavior.

Motivational influences on cognitive control: The role of reward processing

dition (Baumeister, Vohs, & Tice, 2007). When control levels are high, we are able to resist impulses and rapidly correct our behaviour if we inadvertently succumb to temptation. When we lack self-control, behaviours become reflexive and automatic, initiated as a course of habit rather than deliberate exertion. But what factors determine variation in the effectiveness of self-control? Why do we respond to some temptations with renewed vigour in the pursuit of a current goal, while in other situations self-control appears exhausted, allowing impulses and (bad) habits to dominate performance? Here we explore the psychological factors that underlie fluctuations in control, articulating our view that affective processing drives variation in regulatory processes to a larger extent than acknowledged by other treatments of self-control.

Reward processing in the human brain

Publisher Summary Reward processing engages diverse brain regions, including multiple prefrontal regions and the basal ganglia (particularly the multifaceted striatum). Corticostriatal circuits are involved in computation of subjective value for experienced rewards, leading to a valuation signal that can be used to guide future decisions via reinforcement-learning mechanisms. In recent years, an explosion of neuroimaging research has replicated and extended findings from a rich body of animal literature on basic brain reward systems to probe how such systems are modulated by more complex processes that typically influence goal-directed behavior in human society. The goal of this chapter is to discuss the integration of neuroimaging studies of reward processing, with emphasis on cortical-striatal circuits involved in goal-directed behavior and the valuation of reward-related information. Neuroimaging research highlights functional subdivisions within components of this corticostriatal circuitry. Reward processing can be modulated by a number of additional factors, including magnitude of reward, risk, time, and social context. Furthermore, the chapter highlights how cortical-striatal circuits and valuation signals can be modulated by the presence of more complex factors such as risk, time, and social context. Important directions for future research include the study of the complex modulation of reward processing by social factors, as well as processing of aversive information that can also modulate behavior.

Chapter 7 – Reward processing in the human brain: insights from fMRI

Publisher Summary Reward processing engages diverse brain regions, including multiple prefrontal regions and the basal ganglia (particularly the multifaceted striatum). Corticostriatal circuits are involved in computation of subjective value for experienced rewards, leading to a valuation signal that can be used to guide future decisions via reinforcement-learning mechanisms. In recent years, an explosion of neuroimaging research has replicated and extended findings from a rich body of animal literature on basic brain reward systems to probe how such systems are modulated by more complex processes that typically influence goal-directed behavior in human society. The goal of this chapter is to discuss the integration of neuroimaging studies of reward processing, with emphasis on cortical-striatal circuits involved in goal-directed behavior and the valuation of reward-related information. Neuroimaging research highlights functional subdivisions within components of this corticostriatal circuitry. Reward processing can be modulated by a number of additional factors, including magnitude of reward, risk, time, and social context. Furthermore, the chapter highlights how cortical-striatal circuits and valuation signals can be modulated by the presence of more complex factors such as risk, time, and social context. Important directions for future research include the study of the complex modulation of reward processing by social factors, as well as processing of aversive information that can also modulate behavior.