Medial Prefrontal Cortex Stimulation Reduces Retrieval-Induced Forgetting via Fronto-parietal Beta Desynchronization.

The act of recalling memories can paradoxically lead to the forgetting of other associated memories, a phenomenon known as retrieval-induced forgetting (RIF). Inhibitory control mechanisms, primarily mediated by the prefrontal cortex, are thought to contribute to RIF. In this study, we examined whether stimulating the medial prefrontal cortex (mPFC) with transcranial direct current stimulation modulates RIF and investigated the associated electrophysiological correlates. In a randomized study, 50 participants (27 males and 23 females) received either real or sham stimulation before performing retrieval practice on target memories. After retrieval practice, a final memory test to assess RIF was administered. We found that stimulation selectively increased the retrieval accuracy of competing memories, thereby decreasing RIF, while the retrieval accuracy of target memories remained unchanged. The reduction in RIF was associated with a more pronounced beta desynchronization within the left dorsolateral prefrontal cortex (left-DLPFC), in an early time window (<500 ms) after cue onset during retrieval practice. This led to a stronger beta desynchronization within the parietal cortex in a later time window, an established marker for successful memory retrieval. Together, our results establish the causal involvement of the mPFC in actively suppressing competing memories and demonstrate that while forgetting arises as a consequence of retrieving specific memories, these two processes are functionally independent. Our findings suggest that stimulation potentially disrupted inhibitory control processes, as evidenced by reduced RIF and stronger beta desynchronization in fronto-parietal brain regions during memory retrieval, although further research is needed to elucidate the specific mechanisms underlying this effect.

Durability of retrieval-induced forgetting: Effects of different practice schedules.

If retrieval-induced forgetting (RIF) is to play a role in the formation of collective memories, it should be long lasting. Although several studies have found that RIF is short-lived, there is other evidence to suggest that repeated selective practice schedules with a temporal gap between each practice trial may increase the durability of RIF. We tested this possibility in three experiments, focusing on socially shared retrieval-induced forgetting (SSRIF). In two experiments, participants studied scientific or story materials, then listened to someone selectively recall the material repeatedly, either in rapid succession or over an extended time period, and finally recalled the original materials either immediately, after a 1-week delay, or after a 3-week delay. A third experiment examined selective practice in free-flowing conversations. In each instance, RIF was found with repeated selective practice with a temporal gap between trials. The results are discussed in terms of the role RIF might play in the formation of collective memory.

Simulating conversations: A Markov chain model of a central speaker's mnemonic influence over a group of communicating listeners.

Through their selective rehearsal, Central Speakers can reshape collective memory in a group of listeners, both by increasing accessibility for mentioned items (shared practice effects) and by decreasing relative accessibility for related but unmentioned items (socially shared retrieval induced forgetting, i.e., SSRIF). Subsequent networked communication in the group can further modify these mnemonic influences. Extant empirical work has tended to examine such downstream influences on a Central Speaker's mnemonic influence following a relatively limited number of interactions - often only two or three conversations. We develop a set of Markov chain simulations to model the long-term dynamics of such conversational remembering across a variety of group types, based on reported empirical data. These models indicate that some previously reported effects will stabilize in the long-term collective memory following repeated rounds of conversation. Notably, both shared practice effects and SSRIF persist into future steady states. However, other projected future states differ from those described so far in the empirical literature, specifically: the amplification of shared practice effects in communicational versus solo remembering non-conversational groups, the relatively transient impact of social (dis)identification with a Central Speaker, and the sensitivity of communicating networks to much smaller mnemonic biases introduced by the Central Speaker than groups of individual rememberers. Together, these simulations contribute insights into the long-term temporal dynamics of collective memory by addressing questions difficult to tackle using extant laboratory methods, and provide concrete suggestions for future empirical work.

Retrieval-induced forgetting of emotional memories.

Long-term memory manages its contents to facilitate adaptive behaviour, amplifying representations of information relevant to current goals and expediting forgetting of information that competes with relevant memory traces. Both mnemonic selection and inhibition maintain congruence between the contents of long-term memory and an organism's priorities. However, the capacity of these processes to modulate affective mnemonic representations remains ambiguous. Three empirical experiments investigated the consequences of mnemonic selection and inhibition on affectively charged and neutral mnemonic representations using an adapted retrieval practice paradigm. Participants encoded neutral cue words and affectively negative or neutral associates and then selectively retrieved a subset of these associates multiple times. The consequences of selection and inhibitory processes engaged during selective retrieval were evaluated on a final memory test in which recall for all studied associates was probed. Analyses of memory recall indicated that both affectively neutral and negative mnemonic representations experienced similar levels of enhancement and impairment following selective retrieval, demonstrating the susceptibility of affectively salient memories to these mnemonic processes. These findings indicate that although affective memories may be more strongly encoded in memory, they remain amenable to inhibition and flexibly adaptable to the evolving needs of the organism.

Dopamine Modulates Adaptive Forgetting in Medial Prefrontal Cortex.

Active forgetting occurs in many species, but how behavioral control mechanisms influence which memories are forgotten remains unknown. We previously found that when rats need to retrieve a memory to guide exploration, it reduces later retention of other competing memories encoded in that environment. As with humans, this retrieval-induced forgetting relies on prefrontal control processes. Dopaminergic input to the prefrontal cortex is important for executive functions and cognitive flexibility. We found that, in a similar way, retrieval-induced forgetting of competing memories in male rats requires prefrontal dopamine signaling through D1 receptors. Blockade of medial prefrontal cortex D1 receptors as animals encountered a familiar object impaired active forgetting of competing object memories as measured on a later long-term memory test. Inactivation of the ventral tegmental area produced the same pattern of behavior, a pattern that could be reversed by concomitant activation of prefrontal D1 receptors. We observed a bidirectional modulation of retrieval-induced forgetting by agonists and antagonists of D1 receptors in the medial prefrontal cortex. These findings establish the essential role of prefrontal dopamine in the active forgetting of competing memories, contributing to the shaping of retention in response to the behavioral goals of an organism.SIGNIFICANCE STATEMENT Forgetting is a ubiquitous phenomenon that is actively promoted in many species. The very act of remembering some experiences can cause forgetting of others, in both humans and rats. This retrieval-induced forgetting process is thought to be driven by inhibitory control signals from the prefrontal cortex that target areas where the memories are stored. Here we started disentangling the neurochemical signals in the prefrontal cortex that are essential to retrieval-induced forgetting. We found that, in rats, the release of dopamine in this area, acting through D1 receptors, was essential to causing active forgetting of competing memories. Inhibition of D1 receptors impaired forgetting, while activation increased forgetting. These findings are important, because the mechanisms of active forgetting and their linkage to goal-directed behavior are only beginning to be understood.

Remembering and forgetting information about the COVID-19 vaccine on Twitter.

Social media exposes people to selective information of what they have previously known. We conducted two laboratory studies to examine in a simulated online context the phenomenon of retrieval-induced forgetting, where information reposted on social media is likely to be later remembered and relevant but not reposted information may be forgotten. Specifically, we examined how exposure to selective information about the COVID-19 vaccine via tweets affected subsequent memory and whether people's attitudes towards vaccination played a role in their memory for the information. Young adults (N = 119; Study 1) and community members (N = 92; Study 2) were presented with information about the COVID-19 vaccine that included both pro- and anti-vaccine arguments, organised in four categories (i.e., science, children, religion, morality). They then read tweets that repeated half of the arguments from two of the categories. In a subsequent memory test, participants remembered best the statements repeated in the tweets and remembered worst the statements from the same category but not repeated in the tweets, thus exhibiting retrieval-induced forgetting. This pattern of results was similar across pro- and anti-vaccine arguments, regardless of the participants' level of support for vaccination. We discussed the findings in light of remembering and forgetting in the context of the pandemic and social media.

Retrieval-induced forgetting with novel visual stimuli is retrieval-specific and strength- independent.

Retrieval-induced forgetting (RIF) is the phenomenon whereby remembering a subset of learned items can reduce memory for other related items. There are two main explanations for this effect: the competition account and the inhibition account. Most research to date has favoured the inhibition account, though two potential confounds have been identified in the evidence for key predictions of the account: (1) Using binary measures of accuracy may make it difficult to detect correlations between the magnitude of RIF and the increase in recall for practised items that is predicted by the competition account (strength dependence), and (2) typical non-competitive restudy may be too weak a form of practice to elicit detectible RIF effects. The present study aimed to test these contentions by adapting the RIF paradigm to allow a more graded measurement of memory strength and a more active form of non-competitive practice. We trained participants (N = 87) to draw sets of novel shapes from memory, using colour as a category cue and overlaid patterns as individual item recall cues. Responses were graded based on the number of features present and items underwent retrieval practice, copying practice (as a more effective form of restudy), or no practice. The results demonstrated RIF in the retrieval practice condition, but no evidence of RIF in the restudy condition, despite a large memory gain for practised items, supporting the notion of retrieval specificity. There was no evidence of strength dependence in any condition. Our results are consistent with the forgetting in this experiment being driven by inhibition.

Forgetting of competing solutions as a consequence of analogical problem-solving attempts.

ABSTRACTThree experiments used a paradigm based on Retrieval-Induced Forgetting research to test for the competition from non-useful sources of information in cross-domain analogical transfer. This was accomplished by presenting people with texts introducing multiple candidate solutions prior to attempting the Radiation problem, and later testing memory for the texts. In Experiment 1, viable and unviable candidate solutions that varied in surface and structural similarity were presented in their own story contexts. In Experiments 2 and 3, the viable and unviable solutions were embedded within the same story context. The results suggest that forgetting unviable solutions that share surface-level overlap with the target problem may be less important than suggested by prior work. Instead, greater evidence of forgetting was obtained when unviable solutions were embedded within the same context as viable solutions. These findings suggest that competition from superficially similar, unviable solutions may not be the main obstacle during analogical problem-solving attempts, but rather the main obstacle for transfer may be the selection of relevant solution concepts.

Retrieval-induced forgetting in a social task.

Clinical researchers suggest that post-event thinking functions to negatively bias event recall for socially anxious participants. We used a repeated retrieval paradigm to examine the effects of post-event retrieval on memory for social information. Undergraduate participants (n = 214) engaged in an impromptu public speaking task and received a standardised mixture of positive and negative feedback on their speech. Participants in the experimental condition were instructed to repeatedly retrieve the negative feedback items whereas participants in the control condition completed a control task. Both groups were asked to recall the feedback after five minutes and after one week. Results indicated that the experimental group displayed the hypothesised retrieval-induced forgetting effect. In addition, repeated retrieval predicted valence change in that participants recalled the non-retrieved positive feedback items less positively over time. The retrieval-practice effects were distinct from self-reported post-event processing. Contrary to clinical theories, social anxiety did not moderate retrieval-induced forgetting or recall bias. Instead, all participants displayed retrieval-related negatively biased recall.

Retrieval-induced forgetting in a social context: Do the same mechanisms underlie forgetting in speakers and listeners?

Selectively retrieving details from memory can result in forgetting related information, a finding known as retrieval-induced forgetting (RIF). The effect has mostly been examined in individuals, but RIF can also be socially transmitted and arise in listeners who are exposed to a speaker's selective memory retrieval. Whether within-individual RIF (WI-RIF) in speakers and socially shared RIF (SS-RIF) in listeners arise on the basis of the same cognitive mechanisms is unclear, however. In four experiments, we assessed both WI-RIF and SS-RIF while varying final test format to examine the potential involvement of output interference, strength-based blocking, and inhibition. WI-RIF and, to a similar degree, SS-RIF were observed on cued-recall tests with and without controlled output order at test, indicating that output interference cannot account for the observed forgetting. In contrast, SS-RIF was reduced relative to WI-RIF on tests of item recognition. These findings are consistent with the view that inhibition and blocking contribute to both WI-RIF and SS-RIF, but that the contribution of inhibition is reduced in listeners relative to speakers.