Abstract Background When forecasting the future, people often underestimate the likelihood of adverse life events, a phenomenon known as optimism bias. While transcranial alternating current stimulation (tACS) over frontal regions has been employed to modulate various cognitive and emotional functions, its potential impact on optimism bias remains unexplored. Results Using a single-blind, sham-controlled, between-subjects design, we investigated the effects of alpha- and gamma-tACS on optimism bias. Three groups of participants received 15-min of either individualized alpha frequency (IAF)-tACS, 40 Hz-tACS, or sham stimulation over the right frontal cortex during rest. To assess how tACS impacted the optimism bias, participants completed a belief update task before and immediately after the tACS. To assess potential delayed effect of the tACS, participants completed a delay estimation task 24 hours later. We found that across all three groups, participants showed the classic optimism bias, such that they were more likely to update their beliefs toward desirable than undesirable feedback. Notably, compared to the sham and IAF-tACS groups, 40 Hz-tACS further enhanced optimism biases after 24 hours. Conclusion These findings suggest that right frontal gamma- but not alpha-tACS could effectively modulate the long-term optimistic belief updating. Our study highlights the potential of non-invasive brain stimulation as a promising tool for altering optimism biases, which may benefit individuals with pessimistic outlooks.
Abstract Memory consolidation stabilizes newly acquired information. Understanding how individual memories are reactivated during sleep is essential in theorizing memory consolidation. Via unobtrusively re-playing auditory memory cues to sleeping human participants, we identified the reactivation of individual memories during slow-wave sleep (SWS). Using representational similarity analysis (RSA) on cue-elicited electroencephalogram (EEG), we found functionally segregated item-specific representations: the early post-cue EEG activity (0-2 seconds) contained comparable representations for memory cues and for non-memory control cues, thus reflecting sensory processing. Critically, the later EEG activity (2.5-3 s) showed greater item-specific representations for post-sleep remembered items than for forgotten and control cues, demonstrating the reactivation and consolidation of individual memories. Moreover, spindles preferentially supported item-specific memory reactivation for items that were not tested before sleep. These findings delineated how cue-triggered item-specific memory reactivation, subserved by spindles during SWS, contributed to memory consolidation. These results will benefit future research aiming to perturb specific memory episodes during sleep.
Abstract Variability in visual perception in response to consistent stimuli is a fundamental phenomenon linked to fluctuations in prestimulus low-frequency neural oscillations—particularly in the alpha (8–13 Hz) and beta (13–30 Hz) bands—typically measured by their power in electroencephalography (EEG) signals. However, the causal role of these prestimulus alpha and beta power fluctuations in visual perception remains unestablished. In this study, we investigated whether prestimulus alpha and beta power causally affect visual perception using transcranial random noise stimulation (tRNS). In a sham-controlled, single-blind, within-subject design, 29 participants performed a visual detection task while receiving occipital tRNS. Online functional near-infrared spectroscopy (fNIRS) was used to measure cortical excitability during stimulation, and offline EEG signals were collected after stimulation. Mental fatigue was incorporated as a state-dependent factor influencing tRNS effects. Our findings demonstrate that, primarily under low fatigue states, tRNS increased cortical excitability during stimulation (indicated by increased fNIRS oxyhemoglobin amplitude), decreased subsequent prestimulus EEG alpha and beta power, and consequently reduced the visual contrast threshold (VCT), indicating enhanced visual perception. Sensitivity analysis revealed that alpha oscillations contributed more significantly to visual perception than beta oscillations under low fatigue. Additionally, the state-dependent effects of tRNS may result from different sensitivities of VCT to neural oscillations across fatigue states. These results provide causal evidence linking prestimulus alpha and beta power to visual perception and underscore the importance of considering brain states in neuromodulation research. Our study advances the understanding of the neural mechanisms underlying visual perception and suggests potential therapeutic applications targeting neural oscillations. Significance statement Understanding why we perceive identical visual stimuli differently is a fundamental question in neuroscience. This study provides causal evidence that prestimulus alpha and beta neural oscillations directly influence visual perception, particularly under low mental fatigue state. By using tRNS alongside fNIRS and EEG recordings, we demonstrate that modulating neural excitability can alter perceptual outcomes. Our findings highlight the importance of considering brain state—such as fatigue levels—in neuromodulation research. This work advances our understanding of the neural mechanisms underlying visual perception and opens avenues for developing targeted interventions to enhance sensory processing and cognitive functions, potentially benefiting individuals with perceptual or attentional disorders.
People readily change their behavior to comply with others. However, to which extent they will internalize the social influence remains elusive. In this preregistered electroencephalogram (EEG) study, we investigated how learning from one's in-group or out-group members about facial attractiveness would change explicit attractiveness ratings and spontaneous neural representations of facial attractiveness. Specifically, we quantified the neural representational similarities of learned faces with prototypical attractive faces during a face perception task without overt social influence and intentional evaluation. We found that participants changed their explicit attractiveness ratings to both in-group and out-group influences. Moreover, social conformity updated spontaneous neural representation of facial attractiveness, an effect particularly evident when participants learned from their in-group members and among those who perceived tighter social norms. These findings offer insights into how group affiliations and individual differences in perceived social norms modulate the internalization of social influence. Upon learning others' opinions on facial attractiveness, both participants' explicit behavioral ratings and spontaneous neural representation of facial attractiveness changed accordingly.
Daily planning and goal-directed behavior rely on accurate judgments of the duration of past experience. Although retrospective duration judgments are often shorter than the actual time elapsed, how episodic memory changes may impact duration judgments remains unclear. Here, participants watched videos depicting daily events with clear boundaries segmenting each subevent. Participants then completed recall and duration judgment tasks both immediately and after 7 days. Results showed that the recall of the event structure, specifically the number of subevents, significantly influenced immediate and delayed duration judgments. In contrast, memories of gist and number of details had no major impact. However, subevent duration judgments differ, with immediate judgments linked to gist and detail richness, while delayed judgments tend to average out. Together, these results provide new knowledge on the relationship between retrospective duration judgments and memories of naturalistic events, and how such relationship changes over time for different event structures.
The intricate relationship between prestimulus alpha oscillations and visual contrast detection variability has been the focus of numerous studies. However, the causal impact of prestimulus alpha traveling waves on visual contrast detection remains largely unexplored. In our research, we sought to discern the causal link between prestimulus alpha traveling waves and visual contrast detection across different levels of mental fatigue. Using electroencephalography alongside a visual detection task with 30 healthy adults (13 females; 17 males), we identified a robust negative correlation between prestimulus alpha forward traveling waves (FTWs) and visual contrast threshold (VCT). Inspired by this correlation, we utilized 45/-45° phase-shifted transcranial alternating current stimulation (tACS) in a sham-controlled, double-blind, within-subject experiment with 33 healthy adults (23 females; 10 males) to directly modulate these alpha traveling waves. After the application of 45° phase-shifted tACS, we observed a substantial decrease in FTW and an increase in backward traveling waves, along with a concurrent increase in VCT, compared with the sham condition. These changes were particularly pronounced under a low fatigue state. The findings of state-dependent tACS effects reveal the potential causal role of prestimulus alpha traveling waves in visual contrast detection. Moreover, our study highlights the potential of 45/-45° phase-shifted tACS in cognitive modulation and therapeutic applications.
Abstract People tend to view themselves through rose-tinted glasses, as evidenced by preferential recall of positive personality traits. We asked whether reactivating positive personality traits during sleep could enhance peoples’ positive self-evaluative memories. After a baseline self-referential encoding task in which participants endorsed positive and negative traits as self-descriptive, participants were trained to give timely responses to positive traits in a cue-approach training (CAT) task. Once participants had entered slow-wave sleep during a subsequent nap, half of the trained positive traits were unobtrusively re-played to them to promote consolidation (targeted memory reactivation, TMR). Participants completed free-recall tasks about self-descriptive traits to measure their self-evaluative memories. Our findings revealed that TMR prioritized the recall of positive traits that were strongly memorized before sleep, while impairing the recall of intermediate traits. The results suggest pre-TMR self-evaluative memory strength modulated the TMR benefits. Sleep EEG analyses revealed that compared with weak/intermediate/control traits, re-playing strongly memorized traits during sleep elicited greater sigma power changes, which likely reflect preferential memory reactivation. Our results demonstrate the potential implication of wakeful cue-approach training and sleep-based memory reactivation in strengthening positive self-evaluative memories.
Abstract Understanding how individual memory traces are reactivated during sleep is instrumental to the theorizing of memory consolidation, a process during which newly acquired information becomes stabilized and long-lasting. Via targeted memory reactivation (TMR), a technique that unobtrusively delivers learning-related memory cues to sleeping participants, we examined the reactivation of individual memories during slow-wave sleep and how canonical neural oscillations support item-specific memory reactivation. Furthermore, we investigated how pre-sleep testing, which presumably induces fast consolidation before sleep, would modulate sleep-mediated memory reactivation. Applying multivariate representational similarity analysis (RSA) to the cue-elicited electroencephalogram (EEG), we identified significant item-specific representations in two post-cue time windows (620-1350 ms and 2270-3190 ms) for post-sleep remembered items, with only the later item-specific representations contributing to memory consolidation. Untested items (i.e., items that were not tested pre-sleep), but not tested items, elicited higher spindles that predicted stronger item-specific representations and post-sleep memories. Notably, for untested items, the strengths of memory reactivation and spindles were temporally coupled to the up-state of the slow oscillation activity. Together, our results unveiled how item-specific memory reactivation and its link with neural oscillations during sleep contributed to memory consolidation. This knowledge will benefit future research aiming to perturb specific memory episodes during sleep.
Abstract When people are confronted with feedback that counters their prior beliefs, they preferentially rely on desirable rather than undesirable feedback in belief updating, i.e. an optimism bias. In two pre-registered EEG studies employing an adverse life event probability estimation task, we investigated the neurocognitive processes that support the formation and the change of optimism biases in immediate and 24 h delayed tests. We found that optimistic belief updating biases not only emerged immediately but also became significantly larger after 24 h, suggesting an active role of valence-dependent offline consolidation processes in the change of optimism biases. Participants also showed optimistic memory biases: they were less accurate in remembering undesirable than desirable feedback probabilities, with inferior memories of undesirable feedback associated with lower belief updating in the delayed test. Examining event-related brain potentials (ERPs) revealed that desirability of feedback biased initial encoding: desirable feedback elicited larger P300s than undesirable feedback, with larger P300 amplitudes predicting both higher belief updating and memory accuracies. These results suggest that desirability of feedback could bias both online and offline memory-related processes such as encoding and consolidation, with both processes contributing to the formation and change of optimism biases.
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