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Over the past three decades, functional MRI (fMRI) has become key to study how cognitive processes are implemented in the human brain. However, the question of whether participants recruited into fMRI studies differ from participants recruited into other study contexts has received little to no attention. This is particularly pertinent when effects fail to generalize across study contexts: for example, a behavioural effect discovered in a non-imaging context not replicating in a neuroimaging environment. Here, we tested the hypothesis, motivated by preliminary findings (n = 272), that fMRI participants differ from behaviour-only participants on one fundamental individual difference variable: trait anxiety. Analysing trait anxiety scores and possible confounding variables from healthy volunteers across multiple institutions (n = 3317), we found robust support for lower trait anxiety in fMRI study participants, consistent with a sampling or self-selection bias. The bias was larger in studies that relied on phone screening (compared to full in-person psychiatric screening), recruited at least partly from convenience samples (compared to community samples), and in pharmacology studies. Our findings highlight the need for surveying trait anxiety at recruitment and for appropriate screening procedures or sampling strategies to mitigate this bias.

Stressful events are often vividly remembered. Although generally adaptive to survival, this emotional-memory enhancement may contribute to stress-related disorders. We tested here whether the enhanced memory for stressful events is due to the expectancy violation evoked by these events. Ninety-four men and women underwent a stressful or control episode. Critically, to manipulate the degree of expectancy violation, we gave participants either detailed or minimal information about the stressor. Although the subjective and hormonal stress responses were comparable in informed and uninformed participants, prior information about the stressor abolished the memory advantage for core features of the stressful event, tested 7 days later. Using functional near-infrared spectroscopy, we further linked the expectancy violation and memory formation under stress to the inferior temporal cortex. These data are the first to show that detailed information about an upcoming stressor and, by implication, a reduced expectancy violation attenuates the memory for stressful events.

Balancing the exploration of new options and the exploitation of known options is a fundamental challenge in decision-making, yet the mechanisms involved in this balance are not fully understood. Here, we aimed to elucidate the distinct roles of dopamine and noradrenaline in the exploration-exploitation tradeoff during human choice. To this end, we used a double-blind, placebo-controlled design in which participants received either a placebo, 400 mg of the D2/D3 receptor antagonist amisulpride, or 40 mg of the β-adrenergic receptor antagonist propranolol before they completed a virtual patch-foraging task probing exploration and exploitation. We systematically varied the rewards associated with choice options, the rate by which rewards decreased over time, and the opportunity costs it took to switch to the next option to disentangle the contributions of dopamine and noradrenaline to specific choice aspects. Our data show that amisulpride increased the sensitivity to all of these three critical choice features, whereas propranolol was associated with a reduced tendency to use value information. Our findings provide novel insights into the specific roles of dopamine and noradrenaline in the regulation of human choice behavior, suggesting a critical involvement of dopamine in directed exploration and a role of noradrenaline in more random exploration.

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Over the past three decades, MRI has become a key tool to study how cognitive processes are implemented in the human brain. However, the question of whether participants recruited into MRI studies differ from participants recruited into other study contexts has received little to no attention. This is particularly pertinent when effects fail to generalize across study contexts: for example, if a behavioural effect discovered in a non-imaging context does not replicate in a neuroimaging environment. Here, we tested the hypothesis, motivated by preliminary findings (n=272), that MRI study participants differ from behaviour-only study participants on one fundamental individual difference variable: trait anxiety. Analysing a large-scale dataset drawn from multiple institutions (n=3317) and controlling for possible confounding variables, we found robust support for lower trait anxiety in MRI study participants, consistent with a sampling bias. Distributions of trait anxiety scores differed most markedly when psychiatric screening was minimal. Our findings highlight the need for surveying trait anxiety at recruitment and for appropriate screening procedures, in an attempt to mitigate this bias.

Storing motivationally salient experiences preferentially in long-term memory is generally adaptive. Although such relevant experiences are often immediately obvious, a problem arises when the relevance of initially ambiguous events becomes evident sometime after encoding. Is there a mechanism that enables the retroactive enhancement of specific memories? Recent evidence suggests the existence of such a mechanism that selectively strengthens weak memories for neutral stimuli from one category when their respective category gains motivational significance later. Although such a selective retroactive memory enhancement has considerable implications for adaptive memory, evidence for this phenomenon is based on only few studies. Here, we report data from four attempts to replicate category-specific retroactive memory enhancements for neutral stimuli from a category that was later predictive of aversive electric shocks. Although our data showed enhanced memory for the arousing stimuli themselves as well as related subsequent stimuli, none of our experiments provided any evidence for category-specific retroactive memory enhancement when strictly replicating the analysis strategy from the original study. In an additional analysis focusing on high confidence memory only, one of four experiments indicated a significant retroactive memory effect but only in corrected recognition and not in d 0 based on signal detection theory. In an analysis pooled across all experiments, we found a small but significant retroactive memory effect again solely for high-confidence corrected recognition, although the corresponding Bayesian analysis indicated even substantial evidence for the null hypothesis. Overall, our data cast doubt on the reliability and generalizability of the proposed selective retroactive enhancement of initially weak memory.