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.

Mind wandering and sleep in daily life: A combined actigraphy and experience sampling study.

Individuals who sleep poorly report spending more time mind wandering during the day. However, past research has relied on self-report measures of sleep or measured mind wandering during laboratory tasks, which prevents generalization to everyday contexts. We used ambulatory assessments to examine the relations between several features of sleep (duration, fragmentation, and disturbances) and mind wandering (task-unrelated, stimulus-independent, and unguided thoughts). Participants wore a wristband device that collected actigraphy and experience-sampling data across 7 days and 8 nights. Contrary to our expectations, task-unrelated and stimulus-independent thoughts were not associated with sleep either within- or between-persons (n = 164). Instead, individual differences in unguided thoughts were associated with sleep disturbances and duration, suggesting that individuals who more often experience unguided train-of-thoughts have greater sleep disturbances and sleep longer. These results highlight the need to consider the context and features of mind wandering when relating it to sleep.

The effect of sleep on intrusive memories in daily life: a systematic review and meta-analysis of trauma film experiments.

STUDY OBJECTIVES: To synthesize the literature on the effect of sleep versus wake on the frequency and distress of intrusive memories in everyday life after watching film clips with distressing content as a proxy for traumatic experiences. METHODS: We conducted a systematic review by searching PubMed and PsychInfo. The last search was conducted on January 31, 2022. We included experimental studies comparing sleep and wake groups on intrusions using ecological diary methods, whereas studies lacking a wake control condition or relying solely on intrusion-triggering tasks or retrospective questionnaires were excluded. Meta-analyses were performed to evaluate the results. Risks of biases were assessed following the Cochrane guidelines. RESULTS: Across 7 effect sizes from 6 independent studies, sleep (n = 192), as compared to wake (n = 175), significantly reduced the number of intrusive memories (Hedges' g = -0.26, p = .04, 95% CI [-0.50, -0.01]), but not the distress associated with them (Hedges' g = -0.14, p = .25, 95% CI [-0.38, 0.10]). CONCLUSIONS: Although the results suggest that sleep reduces the number of intrusions, there is a strong need for high-powered pre-registered studies to confirm this effect. Risks of biases in the reviewed work concern the selection of the reported results, measurement of the outcome, and failure to adhere to the intervention. Limitations with the current meta-analysis include the small number of studies, which comprised only English-language articles, and the fact that it was not pre-registered.

The association between mnemonic discrimination ability and differential fear learning.

BACKGROUND AND OBJECTIVES: It is important to be able to learn which stimuli in our surroundings predict aversive outcomes. To maintain emotional well-being, it is similarly important to be able to learn which stimuli predict safety. The ability to discriminate between stimuli that predict danger and safety has been suggested to not only have an emotional component, but also a cognitive one. One such candidate mechanism is mnemonic discrimination (MD), the ability to differentiate between two memories that are similar but not identical. In the present study, we wanted to examine if MD performance helps to explain inter-individual differences in the ability to acquire a differentiated fear response during fear conditioning. METHODS: Participants performed a task assessing MD ability, and then underwent a fear conditioning procedure. Fear responses were measured using skin conductance responses (SCRs). RESULTS: Results revealed no support for MD ability being associated with to which degree a differentiated fear response was acquired, or with the time needed to acquire such a response. LIMITATIONS: Our only outcome measurement was SCRs. Future studies need to include fear ratings, expectancy ratings and neural responses. Future studies also need to examine this using a stimulus material where the conditioned stimulus and the safety stimulus are more difficult to distinguish from each other. CONCLUSIONS: If MD ability has a role in inhibiting overgeneralization of fear learning, this does not seem to be driven by MD already during the initial learning.

Does Sleep Selectively Strengthen Certain Memories Over Others Based on Emotion and Perceived Future Relevance?

Sleep has been found to have a beneficial effect on memory consolidation. It has furthermore frequently been suggested that sleep does not strengthen all memories equally. The first aim of this review paper was to examine whether sleep selectively strengthens emotional declarative memories more than neutral ones. We examined this first by reviewing the literature focusing on sleep/wake contrasts, and then the literature on whether any specific factors during sleep preferentially benefit emotional memories, with a special focus on the often-suggested claim that rapid eye movement sleep primarily consolidates emotional memories. A second aim was to examine if sleep preferentially benefits memories based on other cues of future relevance such as reward, test-expectancy or different instructions during encoding. Once again, we first focused on studies comparing sleep and wake groups, and then on studies examining the contributions of specific factors during sleep (for each future relevance paradigm, respectively). The review revealed that although some support exists that sleep is more beneficial for certain kinds of memories based on emotion or other cues of future relevance, the majority of studies does not support such an effect. Regarding specific factors during sleep, our review revealed that no sleep variable has reliably been found to be specifically associated with the consolidation of certain kinds of memories over others based on emotion or other cues of future relevance.

A daytime nap does not increase mnemonic discrimination ability.

It has been proposed that sleep readies the brain for novel learning, and previous work has shown that sleep loss impairs the ability to encode new memories. In the present study, we examined if a daytime nap would increase mnemonic discrimination (MD) performance. MD is the ability to differentiate between memories that are similar but not identical. Participants performed the Mnemonic Similarity Task (MST) twice, once in the morning and once in the afternoon. The goal of this task is to distinguish stimuli that have been seen before from novel stimuli that are similar but not identical. After the morning MST, participants were randomly allocated into either a sleep or a wake group. The sleep group had a 2-hr nap opportunity, whereas the wake group spent a similar amount of time passively resting. All participants then performed a second MST in the afternoon with a novel set of images. Results did not show any support for increased MD ability after a nap. There was, however, a correlation showing that an increase in sleepiness between sessions predicted a decrease in MD performance. Future work must systematically examine how strong sleep manipulations that are needed for sleep to have an effect on encoding ability, as well as which kind of memory tasks that are sensitive to sleep manipulations. More knowledge about the relationship between sleep and the ability to differentiate similar memories from each other is important because impaired MD ability has previously been reported in various groups in which sleep disturbances are also common.

The role of sleep in fear learning and memory.

During the last 10 years, a large body of studies have used fear conditioning paradigms to study the role of sleep in the consolidation of fear and safety learning. This line of research could allow us to answer if it is adaptive or not to sleep in the aftermath of a negative experience, and if sleep has a role in consolidating extinction learning. This field has so far produced several contrasting findings. Thus, this review will not deliver many clear conclusions, but will instead be an attempt to summarize what we know at the moment, to describe the potential clinical applications of this research, and to discuss where to go from here.

The effect of mindfulness training on extinction retention.

Anxiety and trauma related disorders are highly prevalent, causing suffering and high costs for society. Current treatment strategies, although effective, only show moderate effect-sizes when compared to adequate control groups demonstrating a need to develop new forms of treatment or optimize existing ones. In order to achieve this, an increased understanding of what mechanisms are involved is needed. An emerging literature indicates that mindfulness training (MFT) can be used to treat fear and anxiety related disorders, but the treatment mechanisms are unclear. One hypothesis, largely based on findings from neuroimaging studies, states that MFT may improve extinction retention, but this has not been demonstrated empirically. To investigate this question healthy subjects either completed a 4-week MFT- intervention delivered through a smart-phone app (n = 14) or were assigned to a waitlist (n = 15). Subsequently, subjects participated in a two-day experimental protocol using pavlovian aversive conditioning, evaluating acquisition and extinction of threat-related responses on day 1, and extinction retention on day 2. Results showed that the MFT group displayed reduced spontaneous recovery of threat related arousal responses, as compared to the waitlist control group, on day 2. MFT did not however, have an effect on either the acquisition or extinction of conditioned responses day 1. This clarifies the positive effect of MFT on emotional functioning and could have implications for the treatment of anxiety and trauma related disorders.

A more generalized fear response after a daytime nap.

The aim of this study was to examine how a daytime nap affected the consolidation of fear learning. Participants first underwent fear conditioning during which they were exposed to a large and a small circle. One of these was repeatedly paired with an electric shock (making it the CS+), whereas the other circle was never paired with the shock (the CS-). After a delay interval containing either a nap or wake, participants again viewed the CS+ and the CS- intermixed with eight novel circles that varied in size between the two stimuli seen before, as well as a blue triangle that served as a novel stimulus without prior fear relevance. We examined both fear retention (the difference between the CS+ and the CS-) and fear generalization (responses to the novel stimuli based on their similarity to the original CS+). Contrary to previous studies, results from the participants who acquired a differentiated fear response during the acquisition phase revealed that the wake group showed significantly larger skin conductance responses to the CS+ compared to the CS-, whereas no such difference was present in the sleep group. These results were not driven by differences in explicit memory or by differences in general reactivity. Analyzing responses to the novel stimuli revealed a tendency towards a more generalized response in the sleep group, with no differences between the CS+ and any other stimulus, whereas the wake group showed increased responses to the stimuli depending on their similarity to the original CS+. This effect was however only present when controlling for baseline differences in worry.

Sleep and the generalization of fear learning.

Fear conditioning is an important survival mechanism, as is the ability to generalize learned fear responses to stimuli that are similar to the original conditioned stimulus. Overgeneralization of fear learning, prominent in many anxiety disorders, is however highly maladaptive. Because sleep is involved in the consolidation of fear learning, and in active processing of information, the present study explored the effect of sleep on generalization of fear learning. Participants watched a random sequence of pictures of a small and a big circle, one of them coupled with an aversive sound. Then, after a delay period containing either a nap or wake, generalization was examined as participants watched the two circles again, together with eight novel circles that gradually varied in size between the former two. Results showed that the fear response increased as a function of similarity to the conditioned response. However, there was no difference in the degree of generalization between the sleep and the wake group.