Episodic Memory Research Articles

Exploring the links among brain iron accumulation, cognitive performance, and dietary intake in older adults: A longitudinal MRI study

This study evaluated longitudinal brain iron accumulation in older adults, its association with cognition, and the role of specific nutrients in mitigating iron accumulation. MRI-based, quantitative susceptibility mapping estimates of brain iron concentration were acquired from seventy-two healthy older adults (47 women, ages 60–86) at a baseline timepoint (TP1) and a follow-up timepoint (TP2) 2.5–3.0 years later. Dietary intake was evaluated at baseline using a validated questionnaire. Cognitive performance was assessed at TP2 using the uniform data set (Version 3) neuropsychological tests of episodic memory (MEM) and executive function (EF). Voxel-wise, linear mixed-effects models, adjusted for longitudinal gray matter volume alterations, age, and several non-dietary lifestyle factors revealed brain iron accumulation in multiple subcortical and cortical brain regions, which was negatively associated with both MEM and EF performance at T2. However, consumption of specific dietary nutrients at TP1 was associated with reduced brain iron accumulation. Our study provides a map of brain regions showing iron accumulation in older adults over a short 2.5-year follow-up and indicates that certain dietary nutrients may slow brain iron accumulation.

Maternal Methyl-Enriched Diet Improves Episodic Memory and Does Not Affect the Conditioned Fear Memory in Offspring of WAG/RIJ Rats

The purpose of this study is to find out what effect the maternal methyl-enriched diet (MED) in the perinatal period exerts on cognitive functions in adult offspring of WAG/Rij rats, a genetic model of absence epilepsy with comorbid depression. Cognitive functions (learning and memory) were evaluated in tests of a novel object recognition (NOR) and a conditioning of fear memory (fear conditioning). The experiments were carry out on 6-months old male WAG/Rij rats. The mothers of the experimental group fed MED, and the mothers of the control group fed the control diet. The NOR test was used to assess episodic memory. This test is based on innate exploratory motivation (novelty preference motivation), which is usually reduced in depression. The conditioning of fear memory is the classic Pavlovian defensive conditioned reflex, manifested in the form of freezing reactions in response to negative reinforcement (electrical stimulation of paws). In the NOR test, in rats of the experimental group the recognition index (a measure of episodic memory), as well as the number of entries to the center of the arena (a measure of explorative motivation) were significantly higher compared with corresponding measures in the control group. However, no intergroup differences were found in the manifestation of the conditioned fear memory (% of freezing reactions) to the context and sound signal. The results indicate that the maternal MED improves episodic memory in the NOR test, but does not affect the conditioned fear memory associated with context and sound signal in adult offspring of WAG/Rij rats.

Metabotropic NMDAR Signaling Contributes to Sex Differences in Synaptic Plasticity and Episodic Memory.

NMDA receptor (NMDAR) - mediated calcium influx triggers the induction and initial expression of Long-Term Potentiation (LTP). Here we report that in male rodents ion flux-independent (metabotropic) NMDAR signaling is critical for a third step in the production of enduring LTP, i.e., cytoskeletal changes that stabilize the activity-induced synaptic modifications. Surprisingly, females rely upon estrogen receptor alpha (ERα) for the metabotropic NMDAR operations used by males. Blocking NMDAR channels with MK-801 eliminated LTP expression in hippocampal field CA1 of both sexes but left intact theta burst stimulation (TBS)-induced actin polymerization within dendritic spines. A selective antagonist (Ro25-6981) of the NMDAR GluN2B subunit had minimal effects on synaptic responses but blocked actin polymerization and LTP consolidation in males only. Conversely, an ERα antagonist thoroughly disrupted TBS-induced actin polymerization and LTP in females while having no evident effect in males. In an episodic memory paradigm, Ro25-6981 prevented acquisition of spatial locations by males but not females whereas an ERα antagonist blocked acquisition in females but not males. Sex differences in LTP consolidation were accompanied by pronounced differences in episodic memory in tasks involving a minimal (for learning) cue-sampling. Males did better on acquisition of spatial information whereas females had much higher scores than males on tests for acquisition of the identity of cues (episodic 'what') and the order in which the cues were sampled (episodic 'when'). We propose that sex differences in synaptic processes used to stabilize LTP result in differential encoding of the basic elements of episodic memory.Significance Statement Calcium influx through NMDARs has long been recognized as the initiating event for LTP. Results of the present studies call for a substantial revision to this fundamental observation about learning-related synaptic plasticity. Specifically, we show cytoskeletal mechanisms that consolidate field CA1 LTP and episodic memory are triggered not by NMDAR-mediated calcium but by ion flux-independent (metabotropic) signaling. Males used metabotropic functions of the NMDARs for this purpose whereas females relied upon synaptic estrogen receptors. This unprecedented instance of sex differences in synaptic function was accompanied by surprisingly large male/female differences in the acquisition of the three basic elements of episodic memory.

Voice biomarkers in middle and later adulthood as predictors of cognitive changes.

Prosody voice measures, especially jitter and shimmer, have been associated with cognitive impairment and hold potential as early indicators of risk for cognitive decline. Prior research suggests that voice measures assessed concurrently with longitudinal cognitive outcomes are associated with 10-year cognitive declines in middle-age and older adults from Midlife in the U.S. (MIDUS) study. Using a subsample from the same study, we expanded previous research to examine voice measures that were (1) collected 8 years before cognitive outcomes, (2) derived from narrative speech in logical memory tests instead of word list recall tests, and (3) independent of the cognitive outcomes. Multilevel analyses controlled for covariates of age, sex, education, neurological conditions, depressive symptoms, and chronic conditions. The results indicated that higher jitter and lower shimmer predicted greater 10-year declines in episodic memory and working memory. These findings extend previous research by highlighting prosody voice measures assessed 8 years earlier as predictors of subsequent cognitive declines over a decade.

A cross-cultural comparison of intrinsic and extrinsic motivational drives for learning.

Intrinsic motivational drives, like the autonomous feeling of control, and extrinsic motivational drives, like monetary reward, can benefit learning. Extensive research has focused on neurobiological and psychological factors that affect these drives, but our understanding of the sociocultural factors is limited. Here, we compared the effects of autonomy and rewards on episodic recognition memory between students from Dutch and Chinese universities. In an exploratory learning task, participants viewed partially obscured objects that they needed to subsequently remember. We independently manipulated autonomy, as volitional control over an exploration trajectory, as well as the chance to receive monetary rewards. The learning task was followed by memory tests for objects and locations. For both cultural groups, we found that participants learned better in autonomous than non-autonomous conditions. However, the beneficial effect of reward on memory performance was stronger for Chinese than for Dutch participants. By incorporating the sociocultural brain perspective, we discuss how differences in norms and values between Eastern and Western cultures can be integrated with the neurocognitive framework about dorsal lateral and ventral medial prefrontal cortex and dopaminergic reward modulations on learning and memory. These findings have important implications for understanding the neurocognitive mechanisms in which both autonomy and extrinsic rewards are commonly used to motivate students in the realm of education and urge more attention to investigate cultural differences in learning.

An Examination of Episodic Future Thinking and Episodic Memory Among Suicidal and Nonsuicidal Adolescents

ABSTRACT Objective Suicidal individuals experience ambivalent states where they simultaneously consider death and the continuation of their lives. But we have little understanding of how suicidal individuals, particularly youth, mentally construct their future lives. To address this knowledge gap, we aimed to examine episodic future thinking and the related cognitive process of episodic memory among suicidal and nonsuicidal adolescents. Method We administered a performance-based measure of episodic future thinking to community-based adolescents (N = 176, 15–19 years; 69.3% female at birth, 57.1% identifying with a racial minoritized group) and examined the concurrent and predictive validity of details generated within an imagined future event in relation to suicidal ideation (SI; ranging from passive desire of wanting to be dead to active desire to kill oneself). Results Greater difficulty imagining discrete actions within an imagined positive future event was associated with past and subsequent SI, although these associations were largely accounted for by depressive symptoms. In contrast, greater difficulty imagining action-related details tied to either positive or negative future events predicted SI 6 months later controlling for symptoms of both anxiety and depression, SI history, and narrative style. Conclusions Findings from this study offer an initial glimpse into how suicidal adolescents imagine their future and may inform the design of interventions intended to promote a stronger desire for life than death.

Dynamic patterns of functional connectivity in the human brain underlie individual memory formation

Remembering our everyday experiences involves dynamically coordinating information distributed across different brain regions. Investigating how momentary fluctuations in connectivity in the brain are relevant for episodic memory formation, however, has been challenging. Here we leverage the high temporal precision of intracranial EEG to examine sub-second changes in functional connectivity in the human brain as 20 participants perform a paired associates verbal memory task. We first identify potential functional connections by selecting electrode pairs across the neocortex that exhibit strong correlations with a consistent time delay across random recording segments. We then find that successful memory formation during the task involves dynamic sub-second changes in functional connectivity that are specific to each word pair. These patterns of dynamic changes are reinstated when participants successfully retrieve the word pairs from memory. Therefore, our data provide direct evidence that specific patterns of dynamic changes in human brain connectivity are associated with successful memory formation.

A third kind of episodic memory: Context familiarity is distinct from item familiarity and recollection.

Memory for past events is widely believed to operate through two different processes: one called 'recollection' when retrieving confident, specific details of a memory, and another called 'familiarity' when only having an unsure but conscious awareness that an item was experienced before. When people successfully retrieve details such as the source or context of a prior event, it has been assumed to reflect recollection. We demonstrate that familiarity of context is functionally distinct from familiarity of items and recollection and offer a new, tri-component model of memory. The three memory responses were differentiated across multiple behavioral and brain wave measures. What has traditionally been thought to be two kinds of memory processes are actually three, becoming evident when using sensitive enough multi-measures. Results are independently replicated across studies from different labs. These data reveal that context familiarity is a third process of human episodic memory.

Behavioral and electrophysiological evidence for preserved specific associative episodic memory in older adults

Aging is often linked to a decline in associative memory. Prior research has shown that older adults have difficulty retrieving specific associative memory but can retrieve gist associative memory when deliberately differentiating test pairs with different levels of specificity during associative recognition. In this study, we utilized the context reinstatement paradigm to examine whether older adults could retrieve specific memory in situations where associations do not necessarily need to be voluntarily retrieved. Thirty-five older adults were directed to intentionally link objects with unique background scenes during encoding. Subsequently, test objects were presented against either the reinstated or similar background scenes during a recognition memory task, where participants were required to identify whether the objects were old or new regardless of their background contexts. Event-related potentials (ERP) were recorded to uncover the electrophysiological correlates of specific associative episodic memory. Behavioral results revealed higher memory sensitivity for object recognition when the background scenes were reinstated than when those were similar in older adults. ERP results indicated that older adults exhibited a more prominent fronto-centrally distributed positivity during object recognition in the reinstated than in similar contexts. Our results suggest that older adults may preserve their ability to retrieve specific memory for associations through an involuntary, spontaneous recollection process, which holds important theoretical implications for age-related associative memory deficits.

Selective Brain Activations and Connectivities Related to the Storage and Recall of Human Object-Location, Reward-Location, and Word-Pair Episodic Memories.

Different cortical systems to the hippocampus were activated using fMRI during different types of episodic memory task. For object with scene location episodic memory, the activations were high in cortical systems involved in spatial processing, including the ventromedial visual and medial parahippocampal system. These activations for the medial parahippocampal system were higher in the right hemisphere. The activations in the face and object processing ventrolateral visual cortical stream regions FFC, PIT, V8 and TE2p were higher in the object-location in scene task than the reward-location task, and were higher in the right hemisphere. For reward-location in scene episodic memory, activations were also high in the ventromedial visual cortical spatial stream to the hippocampus, but were also selectively high in storage in key reward cortical regions (ventromedial prefrontal 10r, 10v, 10d; pregenual anterior cingulate d32, p24, p32, s32; and medial orbitofrontal cortex reward-related pOFC, 11l, OFC). For word-pair episodic memory, activations were lower in the ventromedial visual and medial parahippocampal spatial cortical stream, and were higher in language-related regions in Broca's area (44, 45, 47l), and were higher in the left hemisphere for these regions and for the many highly connected inferior frontal gyrus regions in the left hemisphere. Further, effective connectivity analyses during the episodic memory tasks showed that the direction of connectivity for these systems was from early visual cortical regions V2-V4 to the ventromedial visual cortical regions VMV1-3 and VVC for spatial scene processing; was from the pregenual anterior cingulate and orbitofrontal cortex reward systems to the hippocampal system; and was from the FFC/V8/PIT system to TE2p in the visual inferior temporal visual cortex, which has connectivity to lateral parahippocampal TF, which in turn has forward effective connectivity to the hippocampus.

The hippocampal CA2 region discriminates social threat from social safety.

The dorsal cornu ammonis 2 (dCA2) region of the hippocampus enables the discrimination of novel from familiar conspecifics. However, the neural bases for more complex social-spatial episodic memories are unknown. Here we report that the spatial and social contents of an aversive social experience require distinct hippocampal regions. While dorsal CA1 (dCA1) pyramidal neurons mediate the memory of an aversive location, dCA2 pyramidal neurons enable the discrimination of threat-associated (CS+) from safety-associated (CS-) conspecifics in both female and male mice. Silencing dCA2 during encoding or recall trials disrupted social fear discrimination memory, resulting in fear responses toward both the CS+ and CS- mice. Calcium imaging revealed that the aversive experience strengthened and stabilized dCA2 representations of both the CS+ and CS- mice, with the incorporation of an abstract representation of social valence into representations of social identity. Thus, dCA2 contributes to both social novelty detection and the adaptive discrimination of threat-associated from safety-associated individuals during an aversive social episodic experience.

Longitudinal association between depressive symptoms and cognitive function: the neurological mechanism of psychological and physical disturbances on memory.

The neural correlates underlying late-life depressive symptoms and cognitive deterioration are largely unclear, and little is known about the role of chronic physical conditions in such association. This research explores both concurrent and longitudinal associations between late-life depressive symptoms and cognitive functions, with examining the neural substrate and chronic vascular diseases (CVDs) in these associations. A total of 4109 participants (mean age = 65.4, 63.0% females) were evaluated for cognitive functions through various neuropsychological assessments. Depressive symptoms were assessed by the Geriatric Depression Scale and CVDs were self-reported. T1-weighted magnetic resonance imaging (MRI), diffusion tensor imaging, and functional MRI (fMRI) data were acquired in a subsample (n = 791). Cognitively, higher depressive symptoms were correlated with poor performance across all cognitive domains, with the strongest association with episodic memory (r = ‒0.138, p < 0.001). Regarding brain structure, depressive symptoms were negatively correlated with thalamic volume and white matter integrity. Further, white matter integrity was found to mediate the longitudinal association between depressive symptoms and episodic memory (indirect effect = -0.017, 95% CI -0.045 to -0.002) and this mediation was only significant for those with severe CVDs (β = -0.177, p = 0.008). This study is one of the first to provide neural evidence elucidating the longitudinal associations between late-life depressive symptoms and cognitive dysfunction. Additionally, the severity of CVDs strengthened these associations, which enlightens the potential of managing CVDs as an intervention target for preventing depressive symptoms-related cognitive decline.

The impact of living environmental factors on cognitive function and mild cognitive impairment: evidence from the Chinese elderly population

ObjectivesMild cognitive impairment represents a pivotal stage in the cognitive decline of older adults, with a considerable risk of advancing to dementia. Recognizing how living environmental factors affect cognition is crucial for crafting effective prevention and intervention strategies. This study seeks to elucidate the relationship between various living environmental factors and cognitive function, with a specific focus on mild cognitive impairment, within a Chinese elderly population.MethodsThis is a cross-section and longitudinal study. Utilizing data from CHARLS, our cross-sectional analysis included 4,401 participants, while the cohort study comprised 3,177 individuals. We assessed living environmental factors based on household fuel types, water sources, indoor temperatures, residential building types, and ambient PM2.5 levels. We employed multiple linear regression for cross-sectional analyses and Cox proportional hazards regression models for longitudinal assessments to determine the effects of living environments on cognitive function and MCI risk. Stratified analyses, interaction tests, and sensitivity analyses were conducted to further validate our findings.ResultsThe findings revealed that, compared to those in high-risk environments, participants in low-risk settings exhibited higher cognitive scores (β = 1.25, 95%CI: 0.85, 1.65), better mental status (β = 0.70, 95%CI: 0.48, 0.92), and improved episodic memory (β = 0.27, 95%CI: 0.13, 0.41). Over a 7-year follow-up, the use of low-risk living environments (HR = 0.67, 95%CI: 0.49, 0.91), including clean fuels (HR = 0.74, 95%CI: 0.57, 0.95) and tap water (HR = 0.84, 95%CI: 0.71, 1.00), demonstrated a protective effect against MCI development. This correlation remained significant regardless of age, gender, residence, education level, smoking, alcohol consumption, and depression.ConclusionThis research provides substantial evidence that living environmental factors significantly affect cognitive function and MCI risk in Chinese older adults. Enhancing living conditions may be a key strategy for promoting cognitive health and preventing MCI in this demographic. Further research is necessary to explore the long-term impacts and potential intervention strategies to optimize living environments for better cognitive outcomes in aging populations.

Prediction errors lead to updating of memories for conversations

ABSTRACT Previous research has established that the brain uses episodic memories to make continuous predictions about the world and that prediction errors, so the mismatch between generated predictions and reality, can lead to memory updating. However, it remains unclear whether prediction errors can stimulate updating in memories for naturalistic conversations. Participants encoded naturalistic dialogues, which were later presented in a modified form. We found that larger modifications were associated with increased learning of the modified statement. Moreover, memory for the original version of the statement was weakened after medium-strong prediction errors, which resulted from the interplay of modification extent and strength of previous memory. After strong prediction errors, both original and modification were well-remembered. Prediction errors thus play a role in keeping representations of statements and therefore socially relevant knowledge about others up to date.

The validity of studying healthy aging with cognitive tests measuring different constructs

A clinically useful characterization of the cognitive aging process requires the development of valid and robust behavioral tests, with an emphasis on explaining and understanding typical inter-individual variability in cognition. Here, using a dataset that includes behavioral scores collected with the National Institute of Health Toolbox Cognition Battery (NIHTB-CB) and other auxiliary tests, we examined (1) the differences between young and old adults across different cognitive domains, (2) the strength of across-subject correlations in behavioral test scores, (3) the consistency of low-dimensional behavioral representations across age using factor analysis, and (4) the accuracy of behavioral scores in predicting participants’ age. Our results revealed that (1) elderly females had better verbal episodic memory scores than elderly males, (2) across-subject correlations between behavioral tests varied with age group, (3) although a three-factor model explained the behavioral data in both age groups, some tasks loaded to different factors between the two groups, and (4) age-performance relationship (i.e. a regression model linking age to cognitive scores) in one group cannot be extrapolated to predict age in the other group, indicating an inconsistency in age-performance relationships across groups. These findings suggest that executive function tests might tap into different cognitive processes in different age groups, which might ultimately suggest that a statistically significant between-group difference in test performance might not always reflect differences in the same underlying cognitive processes. Overall, this study calls for more caution when interpreting age-related differences and similarities between age groups with different cognitive abilities even when the same tests are used.

Adherence to high-frequency ecological momentary assessment in persons with moderate-to-severe traumatic brain injury.

Ecological momentary assessment (EMA) involves repeated collection of real-time self-report data, often multiple times per day, nearly always delivered electronically by smartphone. While EMA has shown promise for researching internal states, behaviors, and experiences in multiple populations, concerns remain regarding its feasibility in samples with cognitive impairments, like those associated with chronic moderate-to-severe traumatic brain injury (TBI). This study examines adherence to a 7-week high-frequency (5x daily) EMA protocol in individuals with moderate-to-severe TBI, considering changes in response rate over time, as well as individual participant characteristics (memory function, education, injury severity, and age). In the sample of 39 participants, the average overall response rate was 65% (range: 5%-100%). Linear mixed-effects modeling revealed a small but statistically significant linear decay in response rate over 7 weeks of participation. Individual trajectories were variable, as evidenced by the significant effect of random slope. A better response rate was positively associated with greater educational attainment and better episodic memory function (statistical trend), whereas the effects of age and injury severity were not significant. These findings shed light on the potential of EMA in TBI studies but underscore the need for tailored strategies to address individual barriers to adherence.

What guides the judgment of learning: Memory or heuristics? An event-related potential study

Memory monitoring ability is essential for the effectiveness of learning processes. Judgment of Learning (JOL), a metacognitive judgment, is commonly used to measure this ability. An ongoing debate questions whether JOL is an outcome of an inferential or recollective experience, as suggested by different hypotheses regarding the underlying cognitive mechanisms of this judgment. To address this question through a neuroscientific perspective, we aimed to investigate the temporal dynamic of JOL adopting event-related potential (ERP) methodology. Seventy-two young adults participated in an episodic memory task involving word-pairs as stimuli. Their JOLs were obtained through categorical choices in a delayed condition. Additionally, their memory performance was tested in the recognition phase. ERP components were compared for different JOL levels, as well as for the hit responses in the recognition test according to their JOL levels. The analyses showed that JOL processes are observable within an early time window after stimulus presentation, as evidenced by elicitation of the P100, N100, P200, N200, and P300 components across all JOL levels. However, only the amplitude of the N100 varied among these levels. A negative ERP component with 330–500 ms latency was also evident for all JOL levels in the central and parietal electrodes, which did not differ in amplitude. The analyses of the recognition phase ERPs showed that the hit responses did not exhibit a significant difference in the familiarity-related mid-frontal old/new effect (FN400) amplitude; however, those with high level of JOL elicited recollection-related parietal old-new effect with a smaller amplitude. These findings support both hypotheses suggesting that JOL is influenced by heuristics and the retrievability of information.

Motifs of human hippocampal and cortical high frequency oscillations structure processing and memory of naturalistic stimuli.

The discrete events of our narrative experience are organized by the neural substrate that underlies episodic memory. This narrative process is segmented into discrete units by event boundaries. This permits a replay process that acts to consolidate each event into a narrative memory. High frequency oscillations (HFOs) are a potential mechanism for synchronizing neural activity during these processes. Here, we use intracranial recordings from participants viewing and freely recalling a naturalistic stimulus. We show that hippocampal HFOs increase following event boundaries and that coincident hippocampal-cortical HFOs (co-HFOs) occur in cortical regions previously shown to underlie event segmentation (inferior parietal, precuneus, lateral occipital, inferior frontal cortices). We also show that event-specific patterns of co-HFOs that occur during event viewing re-occur following the subsequent three event boundaries (in decaying fashion) and also during recall. This is consistent with models that support replay as a mechanism for memory consolidation. Hence, HFOs may coordinate activity across brain regions serving widespread event segmentation, encode naturalistic memory, and bind representations to assemble memory of a coherent, continuous experience.

The impact of disgust learning on memory processes for neutral stimuli: a classical conditioning approach

ABSTRACT Disgust is a basic emotion that promotes pathogen avoidance and can contaminate nearby neutral stimuli. This study investigates how neutral stimuli, which have acquired disgust value through classical conditioning, are processed in episodic memory. The Category Conditioning paradigm was utilised to assign emotional significance to neutral stimuli, followed by a recognition test conducted immediately or 24 h after conditioning (Experiment 1). The results revealed that neutral stimuli that acquired disgust value were recognised with greater accuracy and higher liberal bias compared to other neutral stimuli in the recognition test conducted after 24 h, but not immediately. Present study also indicates that the memory enhancement observed with disgust did not manifest in the context of fear (Experiment 2). Additionally, the results varied when neutral stimuli associated with disgust were presented with disgusting stimuli in recognition test (Experiment 3). Thus, the present study demonstrates that the memory advantage of disgust extends to associated stimuli when they are presented in a list without disgusting stimuli.

Distinct effects of slow and fast theta tACS in enhancing temporal memory

Abstract Temporal memory plays a crucial role in organizing real-life events into meaningful segments. Previous research suggests that the clustering of temporally related information builds on the neural correlates of associative memory, including theta oscillations. Transcranial alternating current stimulation (tACS) provides a means of modulating theta oscillations within associative memory networks, possibly including hippocampal modulation when targeting parietal cortex. Theta oscillations are not limited to a single frequency range, but instead, exhibit functional specialization, with slow theta (3 Hz) implicated in short-term episodic memory formation and fast theta (8 Hz) involved in spatial navigation. This study aimed to investigate the distinct effects of slow and fast theta stimulation on temporal memory. Participants encoded visual objects paired with frame color while receiving tACS stimulation at 8 Hz, 3 Hz, or sham targeting the left parietal cortex. The frame color would change for every eight objects, establishing a context boundary with each color change. Subsequently, participants performed a timeline task to assess temporal memory performance. Results showed that slow, but not fast, theta stimulation led to an enhancement in temporal accuracy (absolute temporal error) compared to sham tACS, in support of our main hypothesis. Under sham stimulation, participants consistently underestimated the temporal position of items presented further away from boundary, compared to those presented at boundary. This finding resembled temporal compression observed during event segmentation. Interestingly, fast, but not slow, theta stimulation reduced this temporal bias (rated position— actual position). This study represents the first tACS evidence for differential contributions of slow versus fast theta to temporal memory formation in humans. We speculate that parietal theta tACS may modulate the hippocampus and facilitate temporal memory formation.