Biology subjects

Akyurek, E.

Publications and source records attributed to Akyurek, E..

9 recordsLinked to original sources

bioRxiv2026

Sleep spindles enhance latent working memory representations

Working memory (WM) allows recently encountered information to be maintained over short periods, yet neural mechanisms supporting this short-term accessibility remain debated. Recent work suggests that WM representations can be maintained without persistent neural firing, in latent synaptic states often termed "activity-silent" memory. Such states can be reactivated by brief perturbations of cortical networks ("pinging"), providing a way to probe otherwise hidden representations. If such latent states rely on synaptic plasticity, they may be sensitive to sleep-dependent recalibration of cortical circuits. Here, we test whether sleep spindles, transient thalamo-cortical oscillations linked to synaptic plasticity, shape post-sleep accessibility of WM representations. Thirty participants performed a visual WM task before and after a daytime nap while high-density EEG was recorded. During the post-nap task, brief visual impulses were used to probe latent WM states, enabling multivariate decoding of memorised content. We show that longer spindle duration during prior NREM sleep predicts both improved post-sleep WM performance and higher-fidelity impulse-evoked decoding of item-specific representations, even when controlling for pre-sleep WM ability. These relationships were selective to spindles; slow-oscillation duration and other oscillatory metrics showed no corresponding effects. Together, our findings link sleep spindle dynamics to the neural readout of activity-silent WM and suggest that sleep-dependent synaptic recalibration optimises cortical circuits for subsequent, short-term information processing.

neuroscience↗

bioRxiv2026

Neural acceleration drives adaptations in working memory encoding speed

Humans and non-human animals adaptively boost their encoding speed when they expect limited sensory exposure time, so that they can capture essential information before it is gone. However, it is unclear how the brain implements this crucial adaptation. Using multivariate pattern analysis of human EEG data, we found that an accelerated neural code underlies adaptations in visual working memory encoding speed.

neuroscience↗

bioRxiv2026

Attentional prioritization enhances the accessibility of neural representations during working memory maintenance

Given the limited capacity of working memory (WM), prioritization is essential for efficient information processing. Whether prioritization acts primarily at encoding, or dynamically shapes representations during maintenance, is currently unclear. Here, we employed a two-item delayed-match-to-sample task and compared prioritization conditions in which the testing order of items was either known in advance or not. Behaviorally, prioritization selectively reduced guess rates, without affecting precision. Using multivariate pattern analysis, we decoded stimulus information from EEG voltage and indexed internal attention using alpha-band patterns. Prioritization did not alter decodable representations during encoding. During maintenance, however, prioritization enhanced both voltage-based decodability and alpha power-based decodability for the currently prioritized item. Mediation analyses further indicated that alpha-based attentional signals influenced behavior indirectly, via voltage-based representational strength, which is consistent with the idea that internal attention supports performance by strengthening prioritized representations during memory maintenance. Significance StatementWM is capacity-limited, requiring the prioritization of information most relevant to current task demands. Whether prioritization is established at encoding or emerges during maintenance, and how it improves working memory performance, remains unclear. Comparing conditions with and without advance priority knowledge, we found that prioritization occurred primarily during maintenance rather than encoding. We also found that prioritization improved performance by directing internal attention to prioritized items, strengthening their neural representations and increasing their accessibility. This finding provides insight into the flexibility of working memory in the updating of already-encoded information.

neuroscience↗

bioRxiv2024

Featural and spatial interference with functionally active and passive items in working memory

Functionally active and passive states in working memory have been related to different neural mechanisms. Memoranda in active states might be maintained by persistent neural firing, whereas memoranda in passive states might be maintained through short-term synaptic plasticity. We reasoned that this might make these items differentially susceptible to interference during maintenance, in particular that passively maintained items might be more robust. To test this hypothesis, we gave our participants a working memory task in which one item was prioritised (active) by always probing it first, while the other item was deprioritised (passive) by always probing it second. In two experiments, on half the trials, we presented an interfering task during memory maintenance, in which the stimuli matched either the feature dimension of the memory items (colour or orientation), or their spatial location. Whether the interfering task appeared on a given trial was unpredictable. In a third experiment where participants were given prior knowledge of the interference condition, and finally in a fourth experiment we used a reward-based prioritisation cue. Across experiments, we found that both active and passive memory items were affected by interference to a similar extent, with overall performance being closely matched in all experiments. We further investigated precision and probability of target response parameters from the standard mixture model, which also showed no differences between states. We conclude that active and passive items, although potentially stored in different neuronal states, do not show differential susceptibility to interference. Public significance statementThe ability to briefly remember information is critical to human cognition. Our so-called working memory is nevertheless rather limited, able to hold only a few items at any one time, and prone to forgetting when we are briefly distracted. Yet, there is reason to believe that not all information in working memory is equally vulnerable. Items that are more passively stored, because they will only be required after some time, might be more resilient to interference. Items that are stored actively, for more immediate recall, might be more easily disrupted. Here, we investigated the effect of an interference task on the retention of both active and passive items in working memory. Our results showed that active and passive items are equally affected by interference, suggesting that resilience in working memory does not depend on the functional state of the items therein.

neuroscience↗

bioRxiv2023

Maintenance of colour memoranda in activity-quiescent working memory states: Evidence from impulse perturbation

The neural mechanisms underlying working memory maintenance pose a challenge for investigation, as sustained neural activity may not always be observable. To address this, the method of impulse perturbation has been employed to examine memorized information during activity-quiescent periods. However, this approach has mainly focused on spatially localized or referenced stimuli, leaving it unclear whether non-spatial memoranda share similar neural maintenance mechanisms. This study aimed to fill this gap by applying the impulse perturbation method to working memory for colours, which are inherently non-spatial stimuli. EEG data from 30 participants performing a delayed match-to-sample task were analysed, with one of the presented items being retro-cued as task-relevant. Our findings indicate that both cued and uncued colours could be decoded from impulse-evoked activity, in contrast to previous reports on working memory for orientation gratings. Additionally, we explored colour decoding from ongoing oscillations in the alpha band and discovered that cued items could be decoded, potentially influenced by attention, whereas uncued items could not. These results suggest subtle differences between the representation of colours and stimuli with spatial properties. However, they also demonstrate that both types of information can be accessed through visual impulse perturbation, regardless of their specific neural states.

neuroscience↗

bioRxiv2023

Impulse perturbation reveals cross-modal access to sensory working memory through learned associations

We investigated if learned associations between visual and auditory stimuli can afford full cross-modal access to working memory. Previous research using the impulse perturbation technique has shown that cross-modal access to working memory is one-sided; visual impulses reveal both auditory and visual memoranda, but auditory impulses do not seem to reveal visual memoranda (Wolff et al., 2020b). Our participants first learned to associate six auditory pure tones with six visual orientation gratings. Next, a delayed match-to-sample task for the orientations was completed, while EEG was recorded. Orientation memories were recalled either via their learned auditory counterpart, or were visually presented. We then decoded the orientation memories from the EEG responses to both auditory and visual impulses presented during the memory delay. Working memory content could always be decoded from visual impulses. Importantly, through recall of the learned associations, the auditory impulse also evoked a decodable response from the visual WM network, providing evidence for full cross-modal access. We also observed that after a brief initial dynamic period, the representational codes of the memory items generalized across time, as well as between perceptual maintenance and long-term recall conditions. Our results thus demonstrate that accessing learned associations in long-term memory provides a cross-modal pathway to working memory that seems to be based on a common coding scheme.

neuroscience↗

bioRxiv2022

Concurrent maintenance of both veridical and transformed working memory representations

In the dynamic environment we live in, the already limited information that human working memory can maintain needs to be constantly updated to optimally guide behaviour. Indeed, previous studies showed that leading up to a response, representations maintained in working memory representations are transformed continuously. This goes hand-in-hand with the removal of task-irrelevant items. However, does such removal also include the representations of stimuli as they were originally, prior to transformation? Here we assessed the neural representation of task-relevant transformed representations, and the no-longer-relevant veridical representations they originated from. We applied multivariate pattern analysis to electroencephalographic data during maintenance of orientation gratings with and without mental rotation. During maintenance, we perturbed the representational network by means of a visual impulse stimulus, and were thus able to successfully decode veridical as well as imaginary, transformed orientation gratings from impulse-driven activity. The impulse response reflected only task-relevant (cued), but not task-irrelevant (uncued) items, suggesting that the latter were quickly discarded from working memory. By contrast, even though the original cued orientation gratings were also no longer task-relevant after mental rotation, these items continued to be represented next to the rotated ones, in different representational formats. This seemingly inefficient use of scarce working memory capacity was associated with reduced probe response times and may thus serve to increase precision and flexibility in guiding behaviour in dynamic environments.

neuroscience↗

bioRxiv2022

Adaptive Encoding Speed in Working Memory

Humans can adapt when complex patterns unfold at a faster or slower pace, for instance when remembering a grocery list that is dictated at an increasingly fast pace. Integrating information over such timescales crucially depends on working memory, but although recent findings have shown that working memory capacity can be flexibly adapted, such adaptations have not yet been demonstrated for encoding speed. In a series of experiments, we found that young adults encoded at a faster rate when they were adapted to overall and recent rate of incoming information. Interestingly, our participants were unable to use explicit cues to speed up encoding, even though these cues were objectively more informative than statistical information. Our findings suggest that adaptive tuning of encoding speed in working memory is a fundamental but largely implicit mechanism underlying our ability to keep up with the pace of our surroundings. Significance StatementHumans can store information very quickly. For instance, when we hear someone speak twice as fast as normal, we can still follow quite well. How is this possible? We hypothesized that when humans expect limited time to store a piece of information (e.g. when listening to a sped-up podcast) they would ideally store that information more quickly before its gone. Indeed, we found that young adults encoded more information per second when they implicitly expect that they have little time to do so. However, they were unable to use explicit cues about how much time they have. It seems that young adults can, at least implicitly, tune the pace at which they store information.

neuroscience↗

bioRxiv2021

Concealed identity information detection with pupillometry in rapid serial visual presentation

The concealed information test (CIT) relies on bodily reactions to stimuli that are hidden in mind. However, people can use countermeasures, such as purposely focusing on irrelevant things, to confound the CIT. A new method designed to prevent countermeasures uses rapid serial visual presentation (RSVP) to present stimuli on the fringe of awareness. Previous studies that used RSVP in combination with electroencephalography (EEG) showed that participants exhibit a clear reaction to their real first name, even when they try to prevent such a reaction (i.e., when their name is concealed information). Since EEG is not easily applicable outside the laboratory, we investigated here whether pupil size, which is easier to measure, can also be used to detect concealed identity information. In our first study, participants adopted a fake name, and searched for this name in an RSVP task, while their pupil sizes were recorded. Apart from this fake name, their real name and a control name also appeared in the task. We found pupil dilation in response to the task-irrelevant real name, as compared to control names. However, while most participants showed this effect qualitatively, it was not statistically significant for most participants individually. In a second study, we preregistered the proof-of-concept methodology and replicated the original findings. Taken together, our results show that the current RSVP task with pupillometry can detect concealed identity information at a group level. Further development of the method is needed to create a valid and reliable concealed identity information detector at the individual level.

physiology↗