Exploration is an important part of decision making and is crucial to maximizing long-term rewards. Past work has shown that people use different forms of uncertainty to guide exploration. In this study, we investigate the role of the pupil-linked arousal system in uncertainty-guided exploration. We measured participants' ( n = 48) pupil dilation while they performed a two-armed bandit task. Consistent with previous work, we found that people adopted a hybrid of directed, random, and undirected exploration, which are sensitive to relative uncertainty, total uncertainty, and value difference between options, respectively. We also found a positive correlation between pupil size and total uncertainty. Furthermore, augmenting the choice model with subject-specific total uncertainty estimates decoded from the pupil size improved predictions of held-out choices, suggesting that people used the uncertainty estimate encoded in pupil size to decide which option to explore. Together, the data shed light on the computations underlying uncertainty-driven exploration. Under the assumption that pupil size reflects locus coeruleus-norepinephrine neuromodulatory activity, these results also extend the theory of the locus coeruleus-norepinephrine function in exploration, highlighting its selective role in driving uncertainty-guided random exploration.

Decisions under uncertainty distinguish between those made under risk (known probabilities) and those made under ambiguity (unknown probabilities). Despite widespread interest in decisions under uncertainty and the successful documentation that these distinct psychological constructs profoundly—and differentially—impact behavior, research has not been able to systematically converge on which brain regions are functionally involved in processing risk and ambiguity. We merge a lesion approach with computational modeling and simultaneous measurement of the arousal response to investigate the impact the medial prefrontal cortex (mPFC), lateral prefrontal cortex (lPFC), and amygdala have on decisions under uncertainty. Results reveal that the lPFC acts as a unitary system for processing uncertainty: Lesions to this region disrupted the relationship between arousal and choice, broadly increasing both risk and ambiguity seeking. In contrast, the mPFC and amygdala appeared to play no role in processing risk, and the mPFC only had a tenuous relationship with ambiguous uncertainty. Together, these findings reveal that only the lPFC plays a global role in processing the highly aversive nature of uncertainty.

Acute stress has been shown to modulate the engagement of different memory systems, leading to preferential expression of stimulus–response (SR) rather than episodic context memory when both types of memory can be used. However, questions remain regarding the cognitive mechanism that underlies this bias in humans—specifically, how each form of memory is individually influenced by stress in order for SR memory to be dominant. Here we separately measured context and SR memory and investigated how each was influenced by acute stress after learning (Experiment 1) and before retrieval (Experiment 2). We found that postlearning stress, in tandem with increased adrenergic activity during learning, impaired consolidation of context memory and led to preferential expression of SR rather than context memory. Preretrieval stress also impaired context memory, albeit transiently. Neither postlearning nor preretrieval stress changed the expression of SR memory. However, individual differences in cortisol reactivity immediately after learning were associated with variability in initial SR learning. These results reveal novel cognitive mechanisms by which stress can modulate multiple memory systems.

Acute stress has frequently been shown to impair cognitive flexibility. Most studies have examined the effect of stress on cognitive flexibility by measuring how stress changes performance in paradigms that require participants to switch between different task demands. These processes typically implicate pFC function, a region known to be impaired by stress. However, cognitive flexibility is a multifaceted construct. Another dimension of flexibility, updating to incorporate relevant information, involves the dorsal striatum. Function in this region has been shown to be enhanced by stress. Using a within-subject design, we tested whether updating flexibility in a DMS task would be enhanced by an acute stress manipulation (cold pressor task). Participants' cortisol response to stress positively correlated with a relative increase in accuracy on updating flexibility (compared with trials with no working memory interference). In contrast, in line with earlier studies, cortisol responses correlated with worse performance when switching between trials with different task demands. These results demonstrate that stress-related increases in cortisol are associated with both increases and decreases in cognitive flexibility, depending on task demands.

Humans remember emotional events not only better but also exhibit a qualitatively distinct recollective experience—that is, emotion intensifies the subjective vividness of the memory, the sense of reliving the event, and confidence in the accuracy of the memory [Phelps, E. A., & Sharot, T. How (and why) emotion enhances the subjective sense of recollection. Current Directions in Psychological Science, 17, 147–152, 2008]. Although it has been demonstrated that activation of the beta-adrenergic system, linked to increases in stress hormone levels and physiological arousal, mediates enhanced emotional memory accuracy, the mechanism underlying the increased subjective sense of recollection is unknown. Behavioral evidence suggests that increased arousal associated with emotional events, either at encoding or retrieval, underlies their increased subjective sense of recollection. Using a double-blind, placebo-controlled, within-subject design, we showed that reducing arousal at encoding through oral intake of 80-mg of the beta-adrenergic receptor antagonist propranolol decreases the subjective sense of recollection for both negative and neutral stimuli 24 hr later. In contrast, administration of propranolol before memory retrieval did not alter the subjective sense of recollection. These results suggest that the neurohormonal changes underlying increased arousal at the time of memory formation, rather than the time of memory retrieval, modulate the subjective sense of recollection.

Previous research has shown that emotional information aids conflict resolution in working memory [WM; Levens, S. M., & Phelps, E. A. Emotion processing effects on interference resolution in working memory. Journal of Emotion, 8, 267–280, 2008]. Using a recency-probes WM paradigm, it was found that positive and negative emotional stimuli reduced the amount of interference created when information that was once relevant conflicted with currently relevant information. To explore the neural mechanisms behind these facilitation effects, an event-related fMRI version of the recency-probes task was conducted using neutral and arousing positive and negative words as stimuli. Results replicate previous findings showing that the left and right inferior frontal gyrus (IFG) is involved in the interference resolution of neutral information and reveal that the IFG is involved in the interference resolution of emotional information as well. In addition, ROIs in the right and left anterior insula and in the right orbital frontal cortex (OFC) were identified that appear to underlie emotional interference resolution in WM. We conclude that the IFG underlies neutral and emotional interference resolution, and that additional regions of the anterior insula and OFC may contribute to the facilitation of interference resolution for emotional information. These findings clarify the role of the insula and OFC in affective and executive processing, specifically in WM conflict resolution.

It is thought that the human amygdala is a critical component of the neural substrates of emotional experience, involved particularly in the generation of fear, anxiety, and general negative affectivity. Although many neuroimaging studies demonstrate findings consistent this notion, little evidence of altered emotional experience following amygdala damage has been gathered in humans. In a preliminary test of the amygdala's role in phenomenal affective states, we assessed the extent of experienced positive and negative affective states in patients with amygdala damage and age-, sex-, and education-matched controls. To assess chronic changes in experienced affect, all groups were administered the Positive and Negative Affect Schedules (PANAS, Watson, Clark, & Tellegen, 1988). In the first study, we examined the effects of amygdala lesions on affective traits in 10 left and 10 right amygdala-damaged patients, 1 patient with bilateral amygdala damage (SP), and 20 control subjects. Subjects were asked to indicate the typicality of different experiential states of positive (e.g., inspired, excited) and negative (e.g., afraid, nervous) valence. In a second study, we examined more closely the effects of bilateral amygdala damage on the day-to-day generation of affective states by administering the PANAS daily for a 30-day period to patient SP and age-, sex-, and education-matched controls. In both experiments, no differences in the magnitude and frequency of self-reported positive or negative affect were found between control subjects and patients with amygdala damage. Moreover, principal components analyses of the covariation among different affects (across individuals in Study 1 and within individuals across days in Study 2) confirmed a two-factor (positive vs. negative) description of experienced affect in controls. A highly similar two-factor description of experienced affect was found in patients with amygdala lesions. This suggests that the underlying structure of affective states was intact following amygdala damage. It is concluded that the human amygdala may be recruited during phenomenal affective states in the intact brain, but is not necessary for the production of these states.

In the present study we report a double dissociation between right and left medial temporal lobe damage in the modulation of fear responses to different types of stimuli. We found that right unilateral temporal lobectomy (RTL) patients, in contrast to control subjects and left temporal lobectomy (LTL) patients, failed to show potentiated startle while viewing negative pictures. However, the opposite pattern of impairment was observed during a stimulus that patients had been told signaled the possibility of shock. Control subjects and RTL patients showed potentiated startle while LTL patients failed to show potentiated startle. We hypothesize that the right medial temporal lobe modulates fear responses while viewing emotional pictures, which involves exposure to (emotional) visual information and is consistent with the emotional processing traditionally ascribed to the right hemisphere. In contrast, the left medial temporal lobe modulates fear responses when those responses are the result of a linguistic/cognitive representation acquired through language, which, like other verbally mediated material, generally involves the left hemisphere. Additional evidence from case studies suggests that, within the medial temporal lobe, the amygdala is responsible for this modulation.

We used fMRI to explore the neural substrates involved in the unconscious evaluation of Black and White social groups. Specifically, we focused on the amygdala, a subcortical structure known to play a role in emotional learning and evaluation. In Experiment 1, White American subjects observed faces of unfamiliar Black and White males. The strength of amygdala activation to Black-versus-White faces was correlated with two indirect (unconscious) measures of race evaluation (Implicit Association Test [IAT] and potentiated startle), but not with the direct (conscious) expression of race attitudes. In Experiment 2, these patterns were not obtained when the stimulus faces belonged to familiar and positively regarded Black and White individuals. Together, these results suggest that amygdala and behavioral responses to Black-versus-White faces in White subjects reflect cultural evaluations of social groups modified by individual experience.