Prof. Dr. Hassan Mahmood Mousa Abo Almaali

– College of Pharmacy Kerbala University
Enabling the Erasure of Unwanted Memories via Subliminal Stimulation

Enhancing the eradication of undesired memories is a complex undertaking, frequently, this requires interaction with prompts tied to the memory, whether factual or imagined, while this approach proves efficacious, it may incite discomfort and potential psychological vulnerabilities, in addition, the manipulation of hippocampal functionality through retrieval suppression leads to the emergence of a captivating amnesic phenomenon, this occurrence interferes with the encoding and stabilization of memories unrelated to the efforts of retrieval inhibition, expanding upon this concept, current article delves into the disruption of distressing memory retention by subtly reintroducing them within this amnesic framework, importantly, it’s noteworthy that while emotionally charged memories undergo unconscious forgetting, the deliberate inhibition of irrelevant and neutral memories, is responsible for the amnesic effect, furthermore, this groundbreaking approach eliminates the need for intentional engagement with disagreeable material, effectively integrating the phenomenon of memory loss with subtle prompts of recall as an approach to deliberate memory suppression
Shifting the focus of attention, the repetitive emergence of intrusive memories and extended rumination carries significance across a spectrum of mental ailments, incorporating conditions like post-traumatic stress disorder (PTSD), acute stress syndrome, and obsessive-compulsive disorder, therapeutic strategies frequently highlight the gradual re-engagement of primary stressors, for example, exposure therapy, a widely employed technique for addressing PTSD, involves the systematic confrontation of triggers associated with traumatic events. Similarly, the technique known as the process of eye movement desensitization and reprocessing (EMDR) demands that patients mentally confront traumatic events while monitoring bilateral stimuli., despite the effectiveness of these direct or imagined re-engagement methods in alleviating symptoms, they can also subject patients to distress, adverse reactions resulting from exposure may lead to discontinuation of therapy and additional risks, thus, the goal is to investigate whether reducing the intrusive nature of unwanted memories can be accomplished without necessitating individuals to consciously relive these distressing experiences.
On the other hand, to address this issue, we propose that unwanted memories might be erased through subliminal reactivation within a specific time frame, this time frame corresponds to the deliberate inhibition of hippocampal processing during voluntary retrieval suppression, this idea arises from an in-depth understanding of the neural mechanisms controlling retrieval suppression and unconscious memory processing, studies on retrieval suppression suggest that intentionally stopping memory retrieval after a cue leads to decreased hippocampal activity, recent research hints at the broader impacts of this action, potentially disrupting various hippocampal functions such as memory formation, retrieval, and consolidation, this disruption resembles natural amnesia, resulting in both backward and forward memory deficits, referred to as the memory shadow, this phenomenon occurs very shortly after each attempt at retrieval suppression (spanning roughly 5–10 seconds before and after suppression), this time frame offers an opportunity to interfere with recently formed or reactivated peripheral memories, however, a memory’s susceptibility to the memory shadow depends on ongoing hippocampal processing that is obstructed by suppression, notably, evidence indicates the reactivation of hippocampal traces without conscious awareness, even cues presented at a subliminal level can activate the hippocampus, responsible for swift associative memory retrieval, in combination, these findings suggest an intriguing possibility; subliminal exposure to reminders in the course of memory shadow induction, brought about by deliberate retrieval inhibition targeting memories unrelated to the context, it is possible that memories relying on the hippocampus might face the risk of being forgotten.

To test this hypothesis, the study explores whether inhibiting retrieval impacts the accessibility of memories subtly prompted during the amnesic period, the Think/No-think (TNT) paradigm is utilized to induce suppression, within this paradigm, participants are involved in trials where they encounter cues for previously learned verbal memory items, it’s worth noting that repeated No-think trials, according to prior research, bring about the vanishing of controlled memories—a phenomenon named suppression-induced forgetting. It’s noteworthy that the effects of these suppression attempts encompass more than just the memories that were intentionally suppressed, leading to the forgetting of entirely unrelated memories (referred to as Bystander memories) linked closely to the No-think trials, hence, the impact of retrieval suppression seems broader, potentially involving a more extensive suppression of hippocampal activity.
Moreover, in earlier investigations, subtle cues (basic visual cues) were introduced to reintroduce previously encoded Bystander memories (situations) between sets of two No-think or two Think trials, this placement aimed to maximize the potential impact on hippocampal processes during the reminder presentation, as both the prior and subsequent No-think trials disturb hippocampal processes, the placement of Bystander reminders between these trials falls within the time frame when memory suppression is in effect, using a technique involving concealed presentation, Bystander reminders were subliminally presented, importantly, participants were not informed that the scenes corresponding to the Bystander objects, presented in between the Think or No-think trials, would be assessed after the completion of the TNT task, this examination involved scenes that were displayed without reminders during the TNT task, used as a baseline control point of reference.

Ultimately, this investigation unveils a noteworthy revelation; the ability of participants to recollect distressing Bystander scenes is hindered in a delayed recall examination due to subconscious exposure to related cues during the amnesic phase, remarkably, this memory impairment emerges even when participants lack conscious recognition of the concealed cues encountered throughout the preceding Think/No-think exercise, notably, the decline in memory observed during the delayed test extends beyond just assessing the scene associated with the same hidden cue used for subconscious reactivation, this finding also includes an unrelated cue that was never discreetly reintroduced during the Think/No-think task. This underscores the all-encompassing disruption of the reactivated scene memory itself as the core explanation for bystander memory forgetting.
References:

⦁ Brewin”, C. R., Gregory, J. D., Lipton, M. et. al., Intrusive images in psychological disorders: Characteristics, neural mechanisms, and treatment implications. Psychology Reviews, 117, 210–232 (2010).

⦁ Anderson, M. C. & Hulbert, J. C. Active forgetting: Adaptation of memory by prefrontal control. Annual, Reviews in Psychology. 72, 1–36, (2021).

⦁ Apsvalka, D., Ferreira,C. S., Schmitz, T.W., et. al., Dynamic targeting enables domain-general inhibitory control over action and thought by the prefrontal cortex. Natural Community”. 13, 274 (2022)