Stress effects on learning and feedback-related neural activity depend on feedback delay.

Depending on feedback timing, the neural structures involved in learning differ, with the dopamine system including the dorsal striatum and anterior cingulate cortex (ACC) being more important for learning from immediate than delayed feedback. As stress has been shown to promote striatum-dependent learning, the current study aimed to explore if stress differentially affects learning from and processing of immediate and delayed feedback. One group of male participants was stressed using the socially evaluated cold pressor test, and another group underwent a control condition. Subsequently, participants performed a reward learning task with immediate (500 ms) and delayed (6,500 ms) feedback while brain activity was assessed with electroencephalography (EEG). While stress enhanced the accuracy for delayed relative to immediate feedback, it reduced the feedback-related negativity (FRN) valence effect, which is the amplitude difference between negative and positive feedback. For the P300, a reduced valence effect was found in the stress group only for delayed feedback. Frontal theta power was most pronounced for immediate negative feedback and was generally reduced under stress. Moreover, stress reduced associations of FRN and theta power with trial-by-trial accuracy. Associations between stress-induced cortisol increases and EEG components were examined using linear mixed effects analyses, which showed that the described stress effects were accompanied by associations between the stress-induced cortisol increases and feedback processing. The results indicate that stress and cortisol affect different aspects of feedback processing. Instead of an increased recruitment of the dopamine system and the ACC, the results may suggest enhanced salience processing and reduced cognitive control under stress.

Good to be stressed? Improved response inhibition and error processing after acute stress in young and older men.

While aging and stress are both known to affect cognitive functions, little is known on whether and how age modulates stress effects on executive functions and their neural correlates. The current study investigated the effect of acute stress on response inhibition and error processing and their underlying cortical processes in younger and older healthy men, using EEG. Forty-nine participants (30 young) were stressed with the Trier Social Stress Test (16 young, 9 older) or underwent a friendly control procedure (14 young, 10 older) and subsequently performed a Go/No-Go task with two levels of task difficulty while performance (reaction time, error rate), stimulus-locked (N2, P3) and response-locked (Ne, Pe) ERPs were measured. Previous results on age-related cognitive deficits were replicated, with slower responses and reduced and delayed N2 and P3 components, as well as reduced Ne and Pe components in older participants. Independent of age, acute stress improved response inhibition, reflected in higher accuracy for compatible trials and enhanced inhibition-related components (N2, P3 and N2d, P3d of the difference waves No-Go minus Go), and improved error processing, reflected in enhanced error-related components (Ne, Pe and Ne_d, Pe_d of the difference waves error minus correct trial). Our findings indicate that acute stress leads to a reallocation of cognitive resources, strengthening inhibition and error processing in young and older healthy men to a similar degree. Neural generators of the analyzed ERPs are mainly part of the salience network, which is upregulated immediately after stress. This offers an explanation as to why response inhibition, in contrast to other executive functions, improves after acute stress.

Stress Elevates Frontal Midline Theta in Feedback-based Category Learning of Exceptions.

Adapting behavior based on category knowledge is a fundamental cognitive function, which can be achieved via different learning strategies relying on different systems in the brain. Whereas the learning of typical category members has been linked to implicit, prototype abstraction learning, which relies predominantly on prefrontal areas, the learning of exceptions is associated with explicit, exemplar-based learning, which has been linked to the hippocampus. Stress is known to foster implicit learning strategies at the expense of explicit learning. Procedural, prefrontal learning and cognitive control processes are reflected in frontal midline theta (4-8 Hz) oscillations during feedback processing. In the current study, we examined the effect of acute stress on feedback-based category learning of typical category members and exceptions and the oscillatory correlates of feedback processing in the EEG. A computational modeling procedure was applied to estimate the use of abstraction and exemplar strategies during category learning. We tested healthy, male participants who underwent either the socially evaluated cold pressor test or a nonstressful control procedure before they learned to categorize typical members and exceptions based on feedback. The groups did not differ significantly in their categorization accuracy or use of categorization strategies. In the EEG, however, stressed participants revealed elevated theta power specifically during the learning of exceptions, whereas the theta power during the learning of typical members did not differ between the groups. Elevated frontal theta power may reflect an increased involvement of medial prefrontal areas in the learning of exceptions under stress.