Biology subjects

Kotchoubey, B.

Publications and source records attributed to Kotchoubey, B..

13 recordsLinked to original sources

bioRxiv2026

One digit too many: brain rhythms and autonomic responses at the limits of working memory capacity

Physiological measures vary with working memory load, but whether they identify when demands exceed a person's working memory capacity remains unclear. We assessed neural and autonomic responses to exceeding digit span by one digit. During an adaptive digit span task, we recorded EEG, pupillometry, and photoplethysmography from 123 participants. We compared each participant's digit span (approximately 70% correct full-sequence recall) with sequences one digit longer (span+1), operationally defined as overload. Full-sequence accuracy decreased from 74.1% to 51.5%, and subjective mental demand increased. Baseline-normalized pulse wave amplitude (PWA) was lower in span+1 from the first digit through terminal retention period. PWA was lower on correctly recalled than erroneous span+1 trials. Phasic pupil responses increased across serial positions but were smaller in span+1 at late span-matched positions; responses did not differ between conditions at their final digits. Non-baseline-corrected pupil diameter was larger in span+1 before sequence onset and during terminal retention, whereas non-baseline-corrected PWA did not differ. Frontal midline theta increased with serial position and was greater during terminal retention in span+1. Alpha and beta power decreased with serial position, and differed between conditions only at late positions. Terminal beta suppression was greater on correctly recalled span+1 trials. Thus, exceeding calibrated span impaired recall without producing a common physiological breakpoint. The findings suggest that reaching this limit does not immediately lead to resource exhaustion or disengagement. Physiological responses showed shifts in timing consistent with adjustments in preparation for recall of the longer sequence, along with increased effort before and during longer sequences.

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bioRxiv2025

Elusive scent of fear: no evidence of olfactory reversal conditioning in humans

Reversal learning offers a window into how associations are acquired, updated, and overwritten. Because olfactory inputs bypass much of the thalamus and are tightly linked to emotion, we examined whether humans can flexibly form and subsequently reverse aversive associations to smells. Thirty healthy adults underwent an olfactory reversal conditioning protocol in which one neutral odor (CS+) was followed by a 90 dB aversive sound (US) and a second odor (CS-) was not. After five blocks the contingencies were reversed. Throughout 300 trials we collected ratings of pleasantness and intensity together with autonomic physiological indices (skin conductance, ECG, photoplethysmography, respiration), facial EMG, and 64-channel EEG. Contrary to expectations, pleasantness, intensity, and all autonomic or facial muscle measures failed to differentiate CS+ and CS-either before or after reversal (all p > .01). Event-related potentials, alpha suppression, heart rate and pulse wave responses likewise showed no CS specificity. Only multivariate classifiers: trained (i) on the time-domain EEG signal and (ii) on alpha-band activity, separately, distinguished CS+ from CS-at above-chance levels in late post-stimulus intervals. These neural signatures did not translate into overt physiological or behavioural differences. The pattern suggests that, at least with neutral odors and an auditory US, olfactory fear learning is subtle, spatially variable across the cortex, and easily masked in group-level averages. Our findings highlight both the promise of multivariate EEG for detecting fragile olfactory associations and the challenge of eliciting robust conditioned responses with cross-modal (odor-sound) pairings.

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bioRxiv2025

Alpha activity during verbal working memory retention depends on the stimulus presentation mode

Previous studies of verbal working memory (WM) have reported inconsistent changes in alpha power during retention, with both increases and decreases observed. We asked whether these discrepancies arise from how stimuli are presented. Thirty adults memorized seven digits presented in four modes: Simultaneous (all digits for 2800 ms) or sequential presentations at Fast (400 ms per digit), Slow (1000 ms per digit), and Fast+delay (400 ms per digit plus a 600 ms free time in between). We analyzed EEG during encoding and a 6 s retention period in theta (4-7 Hz), alpha (8-13 Hz), and beta (18-24 Hz) frequency bands. Encoding produced parametric load-related theta increase and beta decrease, possibly reflecting growing executive control demands and motor program formation, respectively. Alpha power did not scale with load during encoding. Single trial models linked stronger encoding theta and deeper alpha suppression to better recall, whereas retention power did not predict accuracy. During retention, theta and beta were unaffected by presentation mode. Alpha power did not differ significantly when all sequential modes were grouped together compared to the simultaneous mode. However, the Fast+delay mode uniquely showed below-baseline alpha in the first half of the retention. Our findings suggest that alpha dynamics are sensitive to the temporal structure of encoding and retention periods, particularly the presence or absence of free intervals between stimulus presentations. We propose that alpha modulation during WM retention may reflect processes beyond the simple gating of irrelevant sensory information.

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bioRxiv2024

Missing what is right under your nose: failed appetitive and aversive audio-olfactory conditioning in humans

The comparison of physiological mechanisms underlying appetitive and aversive conditioning is often challenging due to the involvement of stimuli from different modalities with potentially disparate effective mechanisms (e.g., pain stimuli versus monetary rewards). The olfactory system offers a unique opportunity to examine both types of conditioning in humans, as isointense odors can serve as comparably pleasant and unpleasant stimuli. To study physiological and behavioral responses during appetitive and aversive learning, we employed odors as unconditioned stimuli (US) in a within-subjects design, measuring various conditioned physiological responses including skin conductance, heart rate, pulse wave amplitude, respiration, fear-potentiated startle, postauricular reflex, facial electromyography as well as event-related potentials, and auditory steady-state responses (ASSR) derived from electroencephalography. We conducted four experiments with a total of 95 participants, presenting three neutral sounds paired with either a pleasant odor, unpleasant odor, or odorless air. The first experiment involved uninstructed participants and frequency-modulated conditioned stimuli (CS) for ASSR analysis. In the second experiment, we omitted the frequency modulation and startle probe. The third experiment included pre-experiment instruction on CS-US contingencies, while the fourth employed a delayed conditioning paradigm in contrast to the other three experiments. Our results revealed differences between CS+ and CS-only in the fear-potentiated startle response in Experiment 3. No other effects were found. The minimal or absent learning effects observed across multiple peripheral and neural physiological measures may be attributed to the extra-thalamic nature of olfactory pathways and the subsequent difficulty in forming associations with auditory stimuli. Impact statementIn a series of 4 experiments, we explored the neurophysiological differences between appetitive and aversive conditioning. Yet, none of the experiments showed effective conditioning. We hypothesize that the lack of learning effects is attributed to the inherent difficulty in forming associations between auditory and olfactory inputs.

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bioRxiv2024

Contingency awareness shapes neural responses in fear conditioning

Contingency awareness refers to an observers ability to identify the association between a conditioned (CS) and an unconditioned stimulus (US). A widely held belief in human fear conditioning is that this form of associative learning may occur independently of contingency awareness. To test this hypothesis, in this preregistered study (https://osf.io/vywq7), we recorded electroencephalography (EEG) during a task, where participants were presented with compounds of a word (drawn from two semantic categories) and tactile stimulation (vibration), followed by either a neutral sound (US-) or a loud noise (US+). Based on interviews, participants were divided into an aware (N=50) and an unaware (N=31) group. Only the aware group showed evidence of learning at the neural level, notably a larger stimulus-preceding negativity developing before US+ and a stronger theta response to vibrations predicting US+. The aware group also showed stronger alpha and beta suppression around the vibrations and a weaker theta response to US+, possibly indicating heightened attention to the cue and the violation/confirmation of expectation. Group differences in alpha and beta suppression were already present before the aversive learning began, suggesting that elevated attention may precede and facilitate awareness. Personality tests showed that elevated anxiety, neuroticism, higher intolerance of uncertainty, or harm avoidance are not predictive to the acquisition of contingency awareness. Our findings support the notion that fear conditioning, as reflected in cortical measures, cannot occur without contingency awareness.

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bioRxiv2023

Task-evoked pulse wave amplitude tracks cognitive load

Cognitive load is a crucial factor in mentally demanding activities and holds significance across various research fields. This study aimed to investigate the effectiveness of pulse wave amplitude (PWA) as a measure for tracking cognitive load and associated mental effort in comparison to heart rate (HR) during a digit span task. The data from 78 participants were included in the analyses. Participants performed a memory task in which they were asked to memorize sequences of 5, 9, or 13 digits, and a control task where they passively listened to the sequences. PWA and HR were quantified from photoplethysmography (PPG) and electrocardiography (ECG), respectively. Pupil dilation was also assessed as a measure of cognitive load. We found that PWA showed a strong suppression with increasing memory load, indicating sensitivity to cognitive load. In contrast, HR did not show significant changes with task difficulty. Moreover, when memory load exceeded the capacity of working memory, a reversal of the PWA pattern was observed, indicating cognitive overload. In this respect, changes in PWA in response to cognitive load correlated with the dynamics of pupil dilation, suggesting a potential shared underlying mechanism. Additionally, both HR and PWA demonstrated a relationship with behavioral performance, with higher task-evoked HR and lower PWA associated with better memory performance. Our findings suggest that PWA is a more sensitive measure than HR for tracking cognitive load and overload. PWA, measured through PPG, holds significant potential for practical applications in assessing cognitive load due to its ease of use and sensitivity to cognitive overload. The findings contribute to the understanding of psychophysiological indicators of cognitive load and offer insights into the use of PWA as a non-invasive measure in various contexts.

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bioRxiv2022

Fear memory in humans is consolidated over time independent of sleep

Fear memories can be altered after acquisition by processes such as fear memory consolidation or fear extinction, even without further exposure to the fear-eliciting stimuli, but factors contributing to these processes are not well understood. Sleep is known to consolidate, strengthen and change newly acquired declarative and procedural memories. However, evidence on the role of time and sleep in the consolidation of fear memories is inconclusive. Here, we used highly sensitive electrophysiological measures to examine the development of fear-conditioned responses over time and sleep in humans. We assessed event-related brain potentials (ERP) in 18 healthy young individuals during fear conditioning before and after a 2-hour afternoon nap or a corresponding wake interval in a counterbalanced within-subject design. The procedure involved pairing a neutral tone (CS+) with a highly unpleasant sound (US). As a control, another neutral tone (CS-) was paired with a neutral sound. Fear responses were examined before the interval during a habituation phase and an acquisition phase as well as after the interval during an extinction phase and a re-acquisition phase. Differential fear conditioning during acquisition was evidenced by a more negative slow ERP component (stimulus-preceding negativity) developing before the unconditioned stimulus (loud noise). This differential fear response was even stronger after the interval during re-acquisition compared to initial acquisition, but this effect was similarly pronounced after sleep and wakefulness. These findings suggest that fear memories are consolidated over time, with this effect being independent of intervening sleep.

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bioRxiv2021

Temporally distinct oscillatory codes of retention and manipulation of verbal working memory

Most psychophysiological studies of working memory (WM) target only the short-term memory construct, while short-term memory is only a part of the WM responsible for the storage of sensory information. Here, we aimed to further investigate oscillatory brain mechanisms supporting the executive components of WM - the part responsible for the manipulation of information. We conducted an exploratory reanalysis of a previously published EEG dataset where 156 participants (82 females) performed tasks requiring either simple retention or retention and manipulation of verbal information in WM. A relatively long delay period (>6s) was employed to investigate the temporal trajectory of the oscillatory brain activity. Compared to baseline, theta activity was significantly enhanced during encoding and the delay period. Alpha-band power decreased during encoding and switched to an increase in the first part of the delay before returning to the baseline in the second part; beta-band power remained below baseline during encoding and the delay. The difference between the manipulation and retention tasks in spectral power had diverse temporal trajectories in different frequency bands. The difference maintained over encoding and the first part of the delay in theta, during the first part of the delay in beta, and during the whole delay period in alpha. Our results suggest that task-related modulations in theta power co-vary with the demands on the executive control network; beta suppression during mental manipulation can be related to the activation of motor networks; alpha is likely to reflect the activation of language areas simultaneously with sensory input blockade.

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bioRxiv2020

The electrophysiological index of the central executive determines verbal working memory capacity

Working memory (WM) consists of short-term storage and executive components. We studied cortical oscillatory correlates of these two components in a large sample of 156 participants to assess separately the contribution of them to individual differences in WM. The participants were presented with WM tasks of above-average complexity. Some of the tasks required only storage in WM, others required storage and mental manipulations. Our data indicate a close relationship between frontal midline theta, central beta activity and the executive components of WM. The oscillatory counterparts of the executive components were associated with individual differences in verbal WM performance. In contrast, alpha activity was not related to the individual differences. The results demonstrate that executive components of WM, rather than short-term storage capacity, play the decisive role in individual WM capacity limits.

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bioRxiv2018

Aversive conditioning in oddball paradigm modulates multisensory integration, attention and emotional processing

The nature of cortical plasticity in the course of learning is one of the most intriguing questions of the modern cognitive neuroscience. Aversive conditioning is a type of associative learning produced by continuous pairing of neutral and aversive stimuli. Aversive conditioning and electroencephalography together provide a good framework for expanding our knowledge about fast learning-related cortical changes. In our experiment we tested a novel paradigm to study associative learning where aversive conditioning was combined with passive oddball. We employed conditioned auditory neutral stimuli and unconditioned aversive electrical shocks and used time-frequency, connectivity and event-related potentials (ERP) analyses to explore their interaction. First, we observed changes in the cortical activity in the form of conditioning-induced multisensory integration. The integration manifested itself in (1) desynchronization of lower beta activity in the contralateral to expected electrical shocks hemisphere and (2) enhanced functional connectivity between auditory and somatosensory cortex in the gamma frequency band. Second, we found a larger amplitude of P3a and the late posterior positivity (LPP) components of ERP to conditioned stimuli, which may be related to increased attentional and emotional significance of these stimuli. Our results reproduced and extended previous findings about multisensory integration in classical conditioning and demonstrated the improved discriminability of ERP responses through incorporation of the oddball paradigm in associative learning.

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bioRxiv2018

A Signature of Passivity? An Explorative Study of the N3 Event-Related Potential Component in Passive Oddball Tasks

Many passive oddball experiments show a negative deflection N3 peaking between 400 and 500 ms, but this wave has never been analyzed properly. We conducted five passive oddball experiments, in which the number of deviants (i.e., one or two), their alleged meaning and their distinctiveness varied. Mastoid- or common-referenced waveforms showed a fronto-central N3 in all experiments. The data were CSD (Current Source Density) transformed and underwent a Principal Component Analysis (PCA). The PCA revealed N3 containing two subcomponents with very stable peak latencies of about 415 and 455 ms, respectively. Both topography of the subcomponents and their variation with experimental conditions were very similar but different from other negative ERP components N1 and N2. The two N3 subcomponents were maximally negative over midfrontal areas but positive over the parietal and particularly over the posterior temporal cortex. Both frontal negativity and posterior positivity exhibited clear oddball effects, i.e., they were larger to deviants than to standards. Positive components P3a and P3b were also analyzed, which replicated the previously known effects. In the Discussion, we speculate about possible meaning of N3; on this basis, specific hypotheses are formulated and further studies are suggested to test these hypotheses.

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bioRxiv2017

Name Conditioning in Event-Related Brain Potentials

Four experiments are reported in which two harmonic tones (CS+ and CS-) were paired with a participants own name (SON) and different names (DN), respectively. A third tone was not paired with any other stimulus and served as a standard (frequent stimulus) in a three-stimuli oddball paradigm. The larger posterior positivity (P3) to SON than DN, found in previous studies, was replicated in all experiments. Conditioning of the P3 response was albeit observed in two similar experiments (1 and 3), but the obtained effects were weak and not identical in the two experiments. Only Experiment 4, where the number of CS/UCS pairings and the Stimulus-Onset Asynchrony between CS and UCS were increased, showed clear CS+/CS- differences both in time and time-frequency domains. Surprisingly, differential responses to CS+ and CS- were also obtained in Experiment 2, although SON and DN in that experiment were masked and never consciously recognized as meaning words (recognition rate 0/63 participants). The results are discussed in the context of other ERP conditioning experiments and, particularly, the studies of non-conscious effect on ERP. Several further experiments are suggested to replicate and extend the present findings and to remove the remaining methodological limitations.

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bioRxiv2017

EEG correlates of working memory performance in females

BackgroundThe study investigates oscillatory brain activity during working memory (WM) tasks. The tasks employed varied in two dimensions. First, they differed in complexity from average to highly demanding. Second, we used two types of tasks, which required either only retention of stimulus set or retention and manipulation of the content. We expected to reveal EEG correlates of temporary storage and central executive components of WM and to assess their contribution to individual differences.\n\nResultsGenerally, as compared with the retention condition, manipulation of stimuli in WM was associated with distributed suppression of alpha1 activity and with the increase of the midline theta activity. Load and task dependent decrement of beta1 power was found during task performance. Beta2 power increased with the increasing WM load and did not significantly depend on the type of the task.\n\nAt the level of individual differences, we found that the high performance (HP) group was characterized by higher alpha rhythm power. The HP group demonstrated task-related increment of theta power in the left anterior area and a gradual increase of theta power at midline area. In contrast, the low performance (LP) group exhibited a drop of theta power in the most challenging condition. HP group was also characterized by stronger desynchronization of beta1 rhythm over the left posterior area in the manipulation condition. In this condition, beta2 power increased in the HP group over anterior areas, but in the LP group over posterior areas.\n\nConclusionsWM performance is accompanied by changes in EEG in a broad frequency range from theta to higher beta bands. The most pronounced differences in oscillatory activity between individuals with high and low WM performance can be observed in the most challenging WM task.

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