Dopaminergic and noradrenergic modulation of stress-induced alterations in brain activation associated with goal-directed behaviour

BACKGROUND: Acute stress is thought to reduce goal-directed behaviour, an effect purportedly associated with stress-induced release of catecholamines. In contrast, experimentally increased systemic catecholamine levels have been shown to increase goal-directed behaviour. Whether experimentally increased catecholamine function can modulate stress-induced reductions in goal-directed behaviour and its neural substrates, is currently unknown. AIM: To assess whether and how experimentally induced increases in dopamine and noradrenaline contribute to the acute stress effects on goal-directed behaviour and associated brain activation. METHODS: One hundred participants underwent a stress induction protocol (Maastricht acute stress test; MAST) or a control procedure and received methylphenidate (MPH) (40 mg, oral) or placebo according to a 2 × 2 between-subjects design. In a well-established instrumental learning paradigm, participants learnt stimulus–response–outcome associations, after which rewards were selectively devalued. Participants’ brain activation and associated goal-directed behaviour were assessed in a magnetic resonance imaging scanner at peak cortisol/MPH concentrations. RESULTS: The MAST and MPH increased physiological measures of stress (salivary cortisol and blood pressure), but only MAST increased subjective measures of stress. MPH modulated stress effects on activation of brain areas associated with goal-directed behaviour, including insula, putamen, amygdala, medial prefrontal cortex, frontal pole and orbitofrontal cortex. However, MPH did not modulate the tendency of stress to induce a reduction in goal-directed behaviour. CONCLUSION: Our neuroimaging data suggest that MPH-induced increases in dopamine and noradrenaline reverse stress-induced changes in key brain regions associated with goal-directed behaviour, while behavioural effects were absent. These effects may be relevant for preventing stress-induced maladaptive behaviour like in addiction or binge eating disorder

The moderating role of conscientiousness in the temporal association between stress and sleep

The personality traits neuroticism and conscientiousness have been associated with sleep problems and the experience of stress. However, the impact of personality on objective sleep and on the temporal relationship between stress and sleep has remained elusive. This study therefore examined whether daytime stress predicts sleep the following night and the moderating role of neuroticism and conscientiousness in this relationship. To introduce stress variability in natural daily stressors, we measured college students (N=99; mean age 21 years; 86% female) during exams (e.g. high academic stress) and at the start of a new course period (e.g. low academic stress). Both objective (actigraphy) and subjective sleep, and daily self-reported stress, were measured for 14 days and personality traits once at the end of the study. Results showed that reported daily stress was significantly higher in the exam period compared to baseline suggesting that our natural manipulation did indeed result in variation in stress levels. Intra-individual daily variations in stress were not associated with the following night's sleep timing, duration, or continuity, implying that more stress during the day did not affect sleep the following night. Higher levels of neuroticism were associated with poorer daily subjective sleep quality and higher stress levels over the complete period. Neuroticism did not moderate the temporal association between stress and sleep. Conscientiousness moderated the association between intra-individual stress and sleep fragmentation and intra-individual stress and wake-up time. This implied that highly conscientious participants experienced reduced sleep fragmentation and earlier awakenings after more stressful days. These results suggest an interconnected relationship among stress, sleep, and personality. Focusing on one aspect, like handling stress or enhancing sleep quality, might yield positive effects on the rest

Controlling intrusive thoughts of future fears under stress

Negative outlooks of our future may foster unwanted and intrusive thoughts. To some extent, individuals have control over their ability to suppress intrusions and downregulate their frequency. Acute stress impairs intentional suppression, leading to an increased frequency of intrusions. The aim of this study was to gain insight into the mechanism underlying stress-induced impairments in intentional suppression of intrusions by investigating the combined and independent roles of the two major stress hormones, noradrenaline and cortisol. Healthy participants (N = 181) were administered propranolol (to block the noradrenergic response), metyrapone (to block the cortisol response), or a placebo before being exposed to the Maastricht Acute Stress Test. Intrusive thoughts of autobiographical future fears were then measured via the Imagine/No-Imagine task. Results demonstrated that the stress response was successfully altered because of the drug and stress manipulations. In all groups, repeated suppression of future fears reduced intrusions. Across the sample, an enhanced decrease over time was associated with greater attenuation of anxiety towards the related fears. The groups did not differ in the total frequency of intrusions. Though, trait anxiety increased the total number of intrusions. Our findings show that stress hormones did not influence the ability to suppress intrusions. However, our results do add support to previous research linking anxiety to memory control deficits. When using autobiographical content, future research should focus on the quality and characteristics of the individual memories to explain more of the variation observed in intentional memory control

Spatio-temporal theta pattern dissimilarity in the right centro-parietal area during memory generalization

Generalization across past events may guide our action in novel situations. Although generalization is a fundamental memory process, its neural underpinnings are not fully understood yet. In the present experiment, we combined Electroencephalography (EEG) with multivariate representational similarity analysis (RSA) to examine in particular the role of spatio-temporal patterns of theta oscillations known to be important for associative memory processes, in memory generalization. We recorded EEG while healthy participants (n = 56) performed an acquired equivalence task. In this task, participants first acquired multiple associations among antecedent and consequent stimuli before they were required to transfer the acquired knowledge to novel stimulus pairs, thus probing memory generalization. Our behavioural data indicated that participants learned the initial associations well and transferred these associations successfully to novel test stimuli, demonstrating successful memory generalization. Our neural data revealed that, compared to mere memory retrieval, generalization was associated with significantly increased pattern dissimilarity of theta activity in the right in the right centro-parietal area (electrodes P4 and P6). This pattern was specific to theta oscillations and not observed in other frequency bands. Our findings suggest an important role of theta oscillations in memory generalization, potentially serving the reactivation and integration of distinct events that enable the generalization across experiences

Cortisol reactivity impairs suppression-induced forgetting

To some extent, we can shape our recollections by intentionally remembering certain experiences while trying to forget others, for example, by intentional suppression. Acute stress impairs suppression-induced forgetting of memories. It is unclear, however, whether these deficits are a direct consequence of the acute stress-induced cortisol response. The present study was designed to examine the stress-induced impairment in suppression-induced forgetting in a subgroup of cortisol responders. We exposed healthy participants to a stress (n = 55) or no-stress control (n = 32) version of the Maastricht Acute Stress Test before they performed the Think / No-Think task. Here, participants aimed to repeatedly retrieve or suppress memories of previously learned cue-target video clips to mimic the complexity of episodic memories. Results on the subsequent memory test revealed that, while the no-stress controls and cortisol non-responders demonstrated suppression-induced forgetting, this effect was absent in cortisol responders. Moreover, the magnitude of suppression-induced forgetting was negatively correlated to stress-induced cortisol increases. The current study extends findings on stress-induced impairments in suppression-induced forgetting by specifically focusing on cortisol reactivity. Furthermore, our findings show the importance of individual differences in cortisol responses as a driving mechanism behind stress-induced alterations in our capacity to actively control our memory