Biology subjects

Filipovic, S.

Publications and source records attributed to Filipovic, S..

5 recordsLinked to original sources

bioRxiv2026

Baseline cognitive abilities shape the effects of tDCS, tACS, and otDCS on object-location memory

Transcranial electrical stimulation (tES) can modulate neural dynamics, yet its effects on memory are heterogeneous. Individual differences in cognitive profiles, may well be one of the potential causes by setting boundary conditions on the extent and mode of the tES-induced modulation of network dynamics. In a sham-controlled, within-subject study (N = 42), we compared the effects of tDCS (1.5 mA), tACS ({+/-}1.0 mA at individual theta frequency, ITF), and otDCS (1.5 mA {+/-} 0.5 mA at ITF) over the left posterior parietal cortex on object-location (OL) associative memory, and examined whether six cognitive abilities (figural reasoning, semantic, visuospatial, processing speed, working memory, mnemonic binding) moderate stimulation outcomes. Associative memory recognition improved selectively under theta-otDCS, whereas tDCS and tACS showed no significant group-level effects. Yet all tES protocols exhibited considerable interindividual variability. Relative to cognitive abilities, processing speed moderated tES effects in line with neural efficiency predictions, yielding greater gains in cognitively faster individuals. In contrast, mnemonic binding and figural reasoning moderated benefits in a compensatory manner, with larger improvements in lower-ability individuals. Overall, the effects of tES on associative memory were specific to the tES protocol and outcome measure while being strongly shaped by cognitive profile via complementing magnification and compensation mechanisms.

neuroscience↗

bioRxiv2025

EEG Microstates Reveal Differential Network Dynamics under Constant Current and Oscillatory Brain Stimulation

BackgroundEEG microstates are brief, quasi-stable scalp topographies that index large-scale network dynamics and may sensitively capture the net effects of transcranial electrical stimulation (tES). ObjectiveTo evaluate differential effects of three types of tES - tDCS, tACS and oscillatory tDCS - (otDCS), on canonical EEG microstates (A-D) in healthy adults. MethodsIn a randomized, sham-controlled, crossover study, 42 participants completed four sessions (tDCS, tACS, otDCS, sham). Stimulation (20 min) used a P3-cheek montage: tDCS +1.5 mA; tACS at individualized theta frequency (ITF, 4-8 Hz), {+/-}1 mA; otDCS anodal with {+/-}0.5 mA oscillation around +1.5 mA at ITF. A five-minute resting EEG (eyes closed then eyes open) was recorded pre- and post-intervention. Microstates were extracted (A-D), back-fitted, and assessed on duration, occurrence, contribution, and mean GFP using linear mixed-effects models with sham and pre/post adjustments. ResultsFour canonical microstates explained ~80% variance with stable topographies across conditions. Modulation patterns were modality-specific. MS A (sensory/arousal) increased across all active protocols, strongest after otDCS. MS B (visual-autobiographical) was consistently suppressed, again most following otDCS. MS C (self-referential) decreased selectively after oscillatory stimulation (tACS, otDCS) only. MS D (executive/attention) diverged by waveform: enhanced by tACS and otDCS but reduced by tDCS. Across outcomes, otDCS produced the largest and most widespread effects, overlapping features of both tDCS (tonic/stabilizing) and tACS (oscillatory/entraining) influences. ConclusionsResting-state EEG microstates provide a sensitive systems-level assay of tES aftereffects. Constant and oscillatory current waveforms reorganize network states in dissociable ways, with otDCS exerting the most robust, comprehensive modulation. These findings support microstates as practical biomarkers for differentiating, optimizing, and monitoring neuromodulation strategies.

neuroscience↗

bioRxiv2025

Individual-specific effects of transcranial electrical stimulation on 40-Hz auditory steady-state responses

Transcranial electrical stimulation (tES) has shown promise for modulating brain function and related behavioral performance, but evidence has been mixed thus far. The possibility of tracking brain activity changes following tES via neurophysiological markers would benefit a better understanding of tES effects and the future development of tES protocols. One promising marker is the auditory steady-state response (ASSR), an externally controlled oscillatory brain activity, typically at 40 Hz, evoked by a periodic auditory stimulus. This study examined the offline effects of different types of tES on 40-Hz ASSR. Participants underwent four conditions of tES, which were applied over the left posterior parietal cortex: transcranial direct current (tDCS), transcranial alternating current (tACS), oscillatory transcranial direct current (otDCS) and sham stimulation. Individually determined theta frequency was delivered in the tACS and otDCS protocols. Following the tES application, electroencephalogram (EEG) was recorded during 40-Hz auditory click stimulation. Mixed-effects modeling revealed no significant group-level differences in phase locking or evoked amplitude between stimulation conditions. However, both baseline (sham) ASSR and the change in ASSR following tES had a substantial interindividual variability. Exploratory analysis showed that individuals with lower baseline ASSR had increased synchronization following tES. Furthermore, the increase in ASSR synchronization was linked to higher memory gain; however, the relationship was observed only in otDCS condition. The findings encourage future research focusing on individual factors that may contribute to tES outcomes.

neuroscience↗

bioRxiv2022

Extraction of individual associative memory related dominant theta frequency for personalized transcranial brain stimulation

Non-invasive brain stimulation (NIBS) has gained increased interest in research and therapy of associative memory (AM) and its impairments. However, the one-size-fits-all approach yields inconsistent findings, thus putting forward the need for the development of personalized frequency-modulated NIBS protocols to increase the focality and the effectiveness of the interventions. There have been only a few attempts to deliver theta frequency-personalized tES. The current study explores the feasibility of determining dominant individual theta-band frequency (ITF) based on AM task evoked EEG activity. In a sample of 42 healthy young adults, we extracted the frequencies (2-15 Hz, in 0.5 Hz steps) with the highest event-related spectral perturbation from the EEG recorded during successful encoding in the AM task. The developed method for extraction of the dominant theta-band frequency based on the AM-evoked EEG changes is able to reliably determine the AM-related ITF and can be used for personalization of the oscillatory NIBS techniques.

neuroscience↗

bioRxiv2019

How Reliable are Prefrontal tDCS Effects - Zero-effects on the Keep-track Task?

Recent neuroimaging studies showed that in addition to the dorsolateral prefrontal cortex (dlPFC), the posterior parietal cortex (PPC) plays a significant role in higher cognitive processes such as executive functions. In this study we aimed to explore the neural underpinnings of executive function of updating by exploring the effects of transcranial direct current stimulation (tDCS) over dlPFC and PCC. Nineteen healthy right-handed participants took part in a cross-over sham-controlled experiment. All participants underwent three tDCS conditions (active tDCS over the left dlPFC; active tDCS over the left PPC; and sham) in counterbalanced order. Following tDCS participants completed the keep-track task, with parallel forms being used in different test-sessions. As a control measure, we used a choice reaction time task. Results showed no significant effects of tDCS regardless of the localization of stimulation. Our results are in contrast with results of other studies exploring prefrontal tDCS effects on updating and do not allow for deriving conclusions about the role of the left PPC in the ability to update information in working memory.

neuroscience↗