Biology subjects

Pedreira, M. E.

Publications and source records attributed to Pedreira, M. E..

8 recordsLinked to original sources

bioRxiv2025

Remoteness sensitive theta network dynamics during early autobiographical memory access

AO_SCPLOWBSTRACTC_SCPLOWAutobiographical memory (AM) is a crucial aspect of human cognition that aids in social understanding, decision-making, and future planning. Its inherent diversity provides a valuable framework for exploring the neural dynamics underlying the retrieval of memories of varying ages. This study aimed to determine whether the access phase of AM retrieval contains neural signatures sensitive to the remoteness of these memories. Forty-one participants engaged in an AM retrieval task while their brain activity was recorded using electroencephalography (EEG). We measured spectral power and time-resolved Granger Causality (GC) during the first 1500 ms following the onset of memory recovery. The results showed that remote autobiographical memories led to a significant increase in midline fronto-central theta power (6.5-8 Hz) around 900 ms after retrieval, compared to recent memories. Additionally, GC analyses revealed that both recent and remote memories showed an anterior-to-posterior flow of information, but the remote network present a denser and more efficient connectivity pattern in the theta band between 800 and 1100 milliseconds. These findings suggest that the remoteness of memories influences the early stages of autobiographical memory access. They also highlight theta power and its directed interactions as temporally precise markers of the neural mechanisms that support autobiographical memory retrieval.

animal behavior and cognition↗

bioRxiv2025

The hidden phase of memory: EEG signatures of reactivation during post-retrieval rest

AO_SCPLOWBSTRACTC_SCPLOWMemory retrieval reactivates previously encoded representations, allowing for their modification and strengthening. However, the neural processes that follow reactivation and contribute to long-term retention remain poorly understood. Here, we examined the post-retrieval resting period to identify neural markers of memory reactivation and their relation to subsequent memory performance. Participants learned pairs of nonsense syllables in multisensory contexts and, on the following day, received either a cue-syllable reminder (context + cue syllable; RX) or a context-only reminder (RCTX) while EEG activity was recorded before and after the reminder presentation. Both reminders elicited significant reductions in beta power (25-40 Hz) during the post-reminder rest, consistent with memory reactivation. The magnitude of beta decrement correlated with better long-term performance. Graph-theoretical analyses of phase synchronization networks in the beta band revealed that the RCTX reminder produced higher bilateral frontal betweenness centrality, suggesting greater engagement of frontal regions in mediating global information flow when retrieving only contextual cues. Moreover, frontal centrality and network density were predictive of subsequent memory accuracy. These findings demonstrate that memory reactivation extends beyond cue presentation into post-retrieval rest, leaving identifiable oscillatory and topological signatures that influence memory persistence. Our results underscore the crucial role of frontal network dynamics and beta-band activity in facilitating long-term memory.

neuroscience↗

bioRxiv2025

Reactivating aversive memories in humans: An EEG and Microstates study of post-retrieval processes

Although fear conditioning is one of the most widely used models to study anxiety in humans, much remains to be explored regarding its underlying neural correlates. In this study, we employed a three-day threat-conditioning protocol in which an angry face (conditioned stimulus, CS+) was paired with an aversive sound (unconditioned stimulus, US). Our main objective was to identify neural markers of post-retrieval processes triggered by the presentation of the CS+ alone, 24 hours after acquisition. We recorded resting-state electroencephalographic (EEG) activity before and after memory reactivation in two groups of participants (females and males counterbalanced): a Reactivation group previously exposed to threat conditioning on Day 1 (n=26) and a Control group (n=26) with no prior conditioning, focusing on memory-related patterns in the frequency domain and microstate dynamics. Our results confirmed successful conditioning and memory retention 48 hours later, as evidenced by implicit, declarative, and emotional responses. Regarding neural activity, we found lower beta-band activity (25-30 Hz) in central brain regions after reactivation, which may reflect enhanced post-reactivation processing of the threat conditioning memory, in contrast to participants who viewed the stimulus for the first time. We observed changes in microstates and a potential link between microstate C and conditioned threat memory. These findings provide initial evidence for neural correlates of post-retrieval processes of an implicit threat memory offering potential relevance for understanding mechanisms implicated in anxiety and related disorders.

neuroscience↗

bioRxiv2025

Reactivation of threat conditioning memory in humans: disentangling the effects on emotional memory and cognitive biases.

Learning to detect and respond to threats is fundamental for survival and is often modeled through threat conditioning (TC) paradigms. While these paradigms reliably produce implicit memories that elicit physiological and behavioral responses to conditioned stimuli (CS), less is explored about how TC influences cognitive and emotional biases, particularly those implicated in anxiety disorders, such as threat overestimation and negative stimulus representation. In this study, we investigated the dynamic interaction between the reactivation of the implicit threat memory and these cognitive biases using a validated TC paradigm in humans. In Experiment 1, participants underwent TC on Day 1, followed by a memory reactivation session (incomplete reminder: one unreinforced CS+) and a highly demanding working memory (HWM) task, used as an amnesic manipulation, or a control condition on Day 2. On Day 3, memory retention was tested using a simplified, single-trial protocol (one CS+, one CS-, and one neutral CS), followed by tasks assessing threat valuation and representation. Results indicated that the HWM task administered post-reactivation significantly reduced skin conductance responses (SCRs) and attenuated cognitive biases, without altering expectancy of the unconditioned stimulus (US). In Experiment 2, we evaluated the effect of varying reactivation frequency (none, one, or two reminders) on implicit memory and cognitive biases. While repeated reactivations generalized the conditioned response to other stimuli, cognitive and emotional biases remained stable, suggesting a dissociation between memory generalization and evaluative processing. These findings demonstrate that implicit threat memories can be selectively modified through post-reactivation interventions, affecting both physiological and cognitive-emotional domains. Importantly, the distinct effects of memory reactivation and reconsolidation on physiological versus cognitive outcomes support the existence of temporally and functionally dissociable mechanisms. This research highlights the need to consider cognitive biases alongside physiological responses when evaluating memory-based interventions and offers novel insight into mechanisms underlying anxiety maintenance and treatment.

neuroscience↗

bioRxiv2023

Recognizing the opponent: the consolidation of long-term social memory in zebrafish males

Recognizing and remembering another individual in a social context could be beneficial for individual fitness. Especially in agonistic encounters, remembering an opponent and the previous fight could allow avoiding new conflicts. Considering this, we hypothesized that this type of social interaction forms a long-term recognition memory lasting several days. It has been shown that a second encounter 24 hours later between the same pair of zebrafish males is resolved with lower levels of aggression. Here, we evaluated if this behavioral change could last for longer intervals and a putative mechanism associated with memory storage: the recruitment of NMDA receptors. We found that if a pair of zebrafish males fight and 48 or 72 hours later fight again, they resolved the second encounter with lower levels of aggression. However, if immediately after the first encounter opponents were exposed to MK-801 (NMDA receptor antagonist), they resolve the second one with the same levels of aggression, that is, no reduction in aggressive behaviors was observed. These results suggest the formation of a long-term social memory related to recognizing a particular opponent and/or the outcome and features of a previous fight.

animal behavior and cognition↗

bioRxiv2021

NON-LINEAR SUSCEPTIBILITY TO INTERFERENCES IN DECLARATIVE MEMORY FORMATION

After encoding, memories go through a labile state followed by a stabilization process known as consolidation. Once consolidated they can enter a new labile state after the presentation of a reminder of the original memory, followed by a period of restabilization (reconsolidation). During these periods of lability the memory traces can be modified. Currently, there are studies that show a rapid stabilization after 30 min, while others show that stabilization occurs after longer periods (e.g. 6 h). Here we investigate the effect of an interference treatment on declarative memory consolidation, comparing distinct time intervals after acquisition. On day 1, participants learned a list of non-syllable pairs (List 1). Immediately after, 30 min, 3 h or 8 h later, they received an interference list (List 2) that acted as an amnesic agent. On day 2 (48 h after training) participants had to recall List 1 first, followed by List 2. We found that the List 1 memory was susceptible to interference when the List 2 was administered immediately or 3 h after learning; however, shortly after acquisition (e.g. 30 min) the List 1 memory becomes transiently protected against interference. We propose the possibility that this rapid memory protection could be induced by a fast and transient neocortical integration (where the memory is transiently protected) becoming partially independent from the hippocampus followed by a hippocampal re-engagement where the memory becomes susceptible to interferences again. Our results open a discussion about the contribution of molecular and systemic aspects to memory consolidation.

neuroscience↗

bioRxiv2020

A working memory intervention weakens the reconsolidation of a threat memory and its biases processing towards threat.

BACKGROUNDThreat-conditioning (TC) memory plays a central role in anxiety disorders, but not in a simple way. This memory impacts on complex cognitive systems by modifying behavioral responses with a bias to fearful stimuli and overestimating potential threats. In this study we proposed a global approach analyzing the scope of disrupting TC memory reconsolidation in the implicit memory, the declarative contingency and the cognitive biases. METHODSDay 1: Subjects were trained on TC. Day 2: after Threat-memory reactivation, one group performed a high demanding working memory task (HWM) and the other a low demanding working memory task (LWM). The last group, only performed the HWM task. Day 3: TC memory was tested by an extinction session followed by reinstatement. Finally, all subjects completed tasks targeting stimuli representation, valuation and attentional bias towards threat. RESULTSDisrupting reconsolidation of TC memory with a HWM weakened the implicit memory retention and faded the representation and valuation towards threat but it had no effect on attentional bias. Moreover, we revealed that subjects performance during the working memory task was specifically associated in TC memory retention. CONCLUSIONSOur findings reveal a strong impairment of the threat-memory restabilization and associated emotional biases. This may result from the competition between defensive survival and central-executive control networks. Our results fits with Experimental Psychopathology approach, disentangling the relation between the implicit memory, cognitive, valenced systems and the possibility to weaken both the threatening memory and the systems associated with the maintenance of anxiety profile.

neuroscience↗

bioRxiv2019

Identification of a Novel Retrieval-Dependent Memory Process in the Crab Neohelice granulata

Fully consolidated associative memories may be altered by alternative retrieval dependent memory processes. While a brief exposure to the conditioned stimulus (CS) can trigger reconsolidation of the original memory, a prolonged CS exposure will trigger memory extinction. The conditioned response is maintained after reconsolidation, but is inhibited after extinction, presumably by the formation of a new inhibitory memory trace. In rats and humans, it has been shown that CS exposure of intermediate duration leave the memory in an insensitive or limbo state. Limbo is characterised by the absence of reconsolidation or extinction. Here we investigated the evolutionary conserved nature of limbo using a contextual Pavlovian conditioning (CPC) memory paradigm in the crab Neohelice granulata. In animals with fully consolidated CPC memory, systemic administration of the protein synthesis inhibitor cycloheximide after 1 CS presentation disrupted the memory, presumably by interfering with memory reconsolidation. The same intervention given after 320 CSs prevented CPC memory extinction. Cycloheximide had no behavioural effect when administered after 80 CS presentations, a protocol that failed to extinguish CPC memory. Also, we observed that a stronger CPC memory engaged reconsolidation after 80 CS instead of limbo, indicating that memory strength affects the parametrical conditions to engage either reconsolidation or limbo. Altogether, these results indicate that limbo is an evolutionary conserved memory process segregating reconsolidation from extinction in the number of CSs space. Limbo appears as an intrinsic component of retrieval dependent memory processing, with a key function in the transition from memory maintenance to inhibition. Author statement (CRediT Roles)Santiago A. Merlo: Conceptualization, Data curation, Formal Analysis, Investigation, Software, Validation, Visualization, Writing - original draft, Writing - review & editing. Jimena Santos: Investigation, Writing - review & editing. Maria Eugenia Pedreira: Conceptualization, Funding acquisition, Project administration, Resources, Supervision, Validation, Writing - original draft, Writing - review & editing. Emiliano Merlo: Conceptualization, Funding acquisition, Project administration, Resources, Supervision, Validation, Writing - original draft, Writing - review & editing.

neuroscience↗