The Index of Intrusion Control (IIC): Capturing individual variability in intentional intrusion control in the laboratory.

Intrusive memories can be downregulated using intentional memory control, as measured via the Think/No-Think paradigm. In this task, participants retrieve or suppress memories in response to an associated reminder cue. After each suppression trial, participants rate whether the association intruded into awareness. Previous research has found that repeatedly exerting intentional control over memory intrusions reduces their frequency. This decrease is often summarised with a linear index, which may miss more complex patterns characterising the temporal dynamics of intrusion control. The goal of this paper is to propose a novel metric of intrusion control that captures those dynamic changes over time as a single index. Results from a mega-analysis of published datasets revealed that the change in intrusion frequencies across time is not purely linear, but also includes non-linear dynamics that seem best captured by a log function of the number of suppression attempts. To capture those linear and non-linear dynamics, we propose the Index of Intrusion Control (IIC), which relies on the integral of intrusion changes across suppression attempts. Simulations revealed that the IIC best captured the linear and non-linear dynamics of intrusion suppression when compared with other linear or non-linear indexes of control, such as the regression slope or Spearman correlation, respectively. Our findings demonstrate how the IIC may therefore act as a more reliable metric to capture individual differences in intrusion control, and examine the role of non-linear dynamics characterizing the conscious access to unwanted memories.

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.

Does stress consistently favor habits over goal-directed behaviors? Data from two preregistered exact replication studies.

Instrumental learning is controlled by two distinct parallel systems: goal-directed (action-outcome) and habitual (stimulus-response) processes. Seminal research by Schwabe and Wolf (2009, 2010) has demonstrated that stress renders behavior more habitual by decreasing goal-directed control. More recent studies yielded equivocal evidence for a stress-induced shift towards habitual responding, yet these studies used different paradigms to evaluate instrumental learning or used different stressors. Here, we performed exact replications of the original studies by exposing participants to an acute stressor either before (cf. Schwabe and Wolf, 2009) or directly after (cf. Schwabe and Wolf, 2010) an instrumental learning phase in which they had learned that distinct actions led to distinct, rewarding food outcomes (i.e., instrumental learning). Then, following an outcome devaluation phase in which one of the food outcomes was consumed until participants were satiated, action-outcome associations were tested in extinction. Despite successful instrumental learning and outcome devaluation and increased subjective and physiological stress levels following stress exposure, the stress and no-stress groups in both replication studies responded indifferently to valued and devalued outcomes. That is, non-stressed participants failed to demonstrate goal-directed behavioral control, thereby rendering the critical test of a shift from goal-directed to habitual control in the stress group inapt. Several reasons for these replication failures are discussed, including the rather indiscriminate devaluation of outcomes that may have contributed to indifferent responding during extinction, which emphasize the need to further our understanding of the boundary conditions in research aimed at demonstrating a stress-induced shift towards habitual control.

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.