Biology subjects

Fiene, M.

Publications and source records attributed to Fiene, M..

7 recordsLinked to original sources

bioRxiv2026

Phase-lag-dependent modulation of interhemispheric β-band functional connectivity by dual-site tACS

Dual-site transcranial alternating current stimulation (ds-tACS) is a promising tool for causally manipulating interhemispheric communication; nevertheless, how different stimulation phase-lags selectively modulate functional connectivity (FC) remains unclear. We recruited 29 healthy participants and included 23 in the final analyses. Participants received 20 Hz ds-tACS over the bilateral primary motor cortices (M1s) using four phase-lags (0, pi/2, pi, 3pi/2) and sham stimulation, combined with recording of high-density EEG before and after stimulation. We quantified the interhemispheric FC using the debiased weighted phase-lag index. No significant differences were found in the average FC changes between overall active stimulation and sham. However, the phase-lag associated with maximum absolute FC changes varied substantially across participants. Accordingly, the assessment of phase-lag-dependency of FC using the Kullback-Leibler distance (DKL) revealed a significant phase-lag-dependent modulation of FC that was transient (limited to the first 5 s after stimulation), restricted to frequencies around the stimulation frequency (18-22 Hz), and occurred without corresponding phase-lag-dependent modulation of the spectral power. In an exploratory analysis, the modulation magnitude showed a quadratic relationship with the individual {beta}-peak FC frequency, where participants with {beta}-peak frequencies farther from the 20 Hz stimulation frequency exhibited stronger effects. These findings indicate that ds-tACS can induce time- and frequency-specific modulation of interhemispheric FC across phase-lags. Given the observed association with individual {beta}-peak connectivity frequency and the variability in the phase-lag associated with maximal FC change, our findings motivate further investigation of personalised neuromodulation protocols.

neuroscience↗

bioRxiv2026

Causal modulation of cortical amplitude coupling through dual-site amplitude-modulated tACS

BackgroundIntrinsic functional coupling at multiple temporal scales is a hallmark of human brain dynamics. Among these coupling modes, slow co-fluctuations of oscillatory amplitudes, termed amplitude coupling, are thought to represent a key organizing principle of the large-scale functional architecture, constraining and gating network activity. Yet, despite extensive correlational evidence, direct causal access to amplitude coupling remains limited, restricting insight into its functional relevance. ObjectivesHere, we investigated whether dual-site amplitude-modulated transcranial alternating current stimulation (AM-tACS) can selectively modulate interhemispheric amplitude coupling in human resting-state networks. MethodsTwenty-eight participants received AM-tACS with a carrier frequency in the beta-band whose amplitude was modulated by low-frequency, scale-free dynamics. By applying dual-site AM-tACS either coherently or incoherently across bilateral parieto-occipital cortices, we tested whether stimulation could systematically enhance or disrupt amplitude co-fluctuations in the electrophysiological aftereffect. ResultsIncoherent AM-tACS significantly reduced interhemispheric amplitude coupling between targeted parieto-occipital cortices, with the strongest effects observed in the stimulated beta-band carrier frequency range. This modulation occurred independently of changes in local power or inter-areal phase coupling, indicating a selective effect of AM-tACS on amplitude-based connectivity. Moreover, reductions in amplitude coupling were correlated with the induced electric field strength, suggesting a dose-dependent relationship between stimulation intensity and coupling modulation. ConclusionsOur findings demonstrate that dual-site AM-tACS can causally and selectively modulate amplitude coupling in the human brain. By establishing causal control over lasting amplitude coupling dynamics, this work provides a methodological foundation for future investigations into the functional and behavioral relevance of amplitude coupling in both healthy and pathological brain states. HighlightsO_LIDual-site AM-tACS selectively modulates amplitude coupling in humans C_LIO_LIAM-tACS was designed to mimic natural, scale-free amplitude fluctuations C_LIO_LIStimulation effects are spatially confined to interactions between target regions C_LIO_LIE-field strength predicts the change in amplitude coupling, suggesting a dose-response relationship C_LIO_LIAmplitude coupling modulations are not mediated by band-limited power changes C_LI

neuroscience↗

bioRxiv2024

Delta phase-dependent modulation of temporal predictions by parietal transcranial alternating current stimulation

BackgroundPrevious research has shown that temporal prediction processes are associated with phase resets of low-frequency delta oscillations in a network of parietal, sensory and frontal areas during non-rhythmic sensory stimulation. Transcranial alternating current stimulation (tACS) modulates perceptually relevant brain oscillations in a frequency and phase-specific manner, allowing the assessment of their functional qualities in certain cognitive functions like temporal prediction. ObjectiveWe addressed the relation between oscillatory activity and temporal prediction by using tACS to manipulate brain activity in a sinusoidal manner. This enables the investigation of the relevance of low-frequency oscillations phase for temporal prediction. MethodsDelta tACS was applied over the left and right parietal cortex in two separate unimodal and crossmodal experiments. Participants judged either the visual or the tactile reappearance of a uniformly moving visual stimulus, which shortly disappeared behind and occluder. Using an intermittent electrical stimulation protocol, tACS was applied with six different phase shifts relative to sensory stimulation in both experiments while participants performed a temporal prediction task. Additionally, a computational model was developed and analysed to elucidate oscillation-based functional principles for the generation of temporal predictions. ResultsOnly in the unimodal experiment, the application of delta tACS resulted in a phase-dependent modulation of temporal prediction performance. By considering the effect of sustained tACS in the computational model, we demonstrate that the entrained dynamics can phase-specifically modulate temporal prediction accuracy. ConclusionOur findings suggest that phase-specific neuromodulation through delta tACS can influence temporal prediction accuracy in a unimodal context. This provides support to the notion that low-frequency delta oscillations are of causal relevance for temporal prediction.

neuroscience↗

bioRxiv2023

Transcranial electrical stimulation over premotor cortex mimics attentional modulation of visual processing

Attentional control over sensory processing has been linked to neural alpha oscillations and related pulsed inhibition of the human cortex. Despite the wide consensus on the functional relevance of alpha oscillations for attention, precise neural mechanisms of how alpha oscillations shape perception and how this top-down modulation is implemented in cortical networks remain unclear. Here, we tested the hypothesis that alpha oscillations in premotor cortex are causally involved in top-down regulation of visual cortex responsivity to contrast. We applied intermittent transcranial alternating current stimulation (tACS) over bilateral premotor cortex to manipulate attentional preparation in a visual discrimination task. tACS was applied at 10 Hz (alpha) and controlled with 40 Hz (gamma) and sham stimulation. Importantly, we used a novel linear mixed modeling approach for statistical control of neurosensory side-effects of the electric stimulation. We found a frequency-specific effect of alpha tACS on the slope parameter, leading to enhanced low-contrast perception and decreased perception of high-contrast stimuli. Side-effects affected both threshold and slope parameters, leading to high variability in parameter estimates. Controlling the impact of side-effects on psychometric parameters by linear mixed model analysis reduced variability and clarified the existing effect. We conclude that alpha tACS over premotor cortex mimicked a state of increased endogenous attention potentially by modulation of fronto-occipital connectivity in the alpha band. We speculate that this network modulation allowed for improved sensory readout from visual cortex which led to a decrease in psychometric slope, effectively broadening the dynamic range for contrast perception. Significance statementAttention is fundamental to voluntary control of perception and behavior. Yet, despite extensive scientific efforts, precise underlying neural mechanisms remain elusive. We contribute to this ongoing discussion by providing evidence for a vital role of frontal alpha oscillations in regulating the responsivity of visual cortex. By controlled neuromodulation with intermittent transcranial alternating current stimulation (tACS), we show that alpha tACS modulates psychometric properties of visual contrast perception. This study fills an important gap between work on alpha oscillations in spatial attention and studies on the psychometrics of attention. Furthermore, we pioneered an approach for the statistical control of tACS side-effects with linear mixed modeling and thereby add to the ongoing debate on outcome variability in studies using transcranial neurostimulation methods.

neuroscience↗

bioRxiv2023

Personalized alpha-tACS targeting left posterior parietal cortex modulates visuo-spatial attention and posterior evoked EEG activity

BackgroundCovert visuo-spatial attention is marked by the anticipatory lateralization of neuronal alpha activity in the posterior parietal cortex. Previous applications of transcranial alternating current stimulation (tACS) at the alpha frequency, however, were inconclusive regarding the causal contribution of oscillatory activity during visuo-spatial attention. ObjectiveAttentional shifts of behavior and electroencephalography (EEG) after-effects were assessed in a cued visuo-spatial attention paradigm. We hypothesized that parietal alpha-tACS facilitates attention in the ipsilateral visual hemifield. Furthermore, we assumed that modulations of behavior and neurophysiology are related to individual electric field simulations. MethodsWe applied personalized tACS at alpha and gamma frequencies to elucidate the role of oscillatory neuronal activity for visuo-spatial attention. Personalized tACS montages were algorithmically optimized to target individual left and right parietal regions that were defined by an EEG localizer. ResultsBehavioral performance in the left hemifield was specifically increased by alpha-tACS compared to gamma-tACS targeting the left parietal cortex. This hemisphere-specific effect was observed despite the symmetry of simulated electric fields. In addition, visual event-related potential (ERP) amplitudes showed a reduced lateralization over posterior sites induced by left alpha-tACS. Neuronal sources of this effect were localized in the left premotor cortex. Interestingly, accuracy modulations induced by left parietal alpha-tACS were directly related to electric field magnitudes in the left premotor cortex. ConclusionOverall, results corroborate the notion that alpha lateralization plays a causal role in covert visuo-spatial attention and indicate an increased susceptibility of parietal and premotor brain regions of the left dorsal attention network to subtle tACS-neuromodulation.

neuroscience↗

bioRxiv2021

Electrical neuromodulation biases brightness perception of flickering light

BackgroundVisual phenomena like brightness illusions impressively demonstrate the highly constructive nature of perception. In addition to physical illumination, the subjective experience of brightness is related to temporal neural dynamics in visual cortex. ObjectiveHere, we asked whether biasing the temporal pattern of neural excitability in visual cortex by transcranial alternating current stimulation (tACS) modulates brightness perception of concurrent rhythmic visual stimuli. MethodsParticipants performed a brightness discrimination task of two flickering lights, one of which was targeted by same-frequency electrical stimulation at varying phase shifts. tACS was applied with an occipital and a periorbital active control montage, based on simulations of electrical currents using finite-element head models. ResultsExperimental results reveal that flicker brightness perception is modulated dependent on the phase shift between sensory and electrical stimulation, solely under occipital tACS. Phase-specific modulatory effects by tACS were dependent on flicker-evoked neural phase stability at the tACS-targeted frequency, recorded prior to electrical stimulation. The optimal timing of tACS application leading to enhanced brightness perception was further correlated with the neural phase delay of the cortical flicker response. ConclusionsOur results corroborate the role of temporally coordinated neural activity in visual cortex for brightness perception of rhythmic visual input in humans. Phase-specific behavioral modulations by tACS emphasize its efficacy to transfer perceptually relevant temporal information to the cortex. These findings provide an important step towards understanding the basis of visual perception and further confirm electrical stimulation as a tool for advancing controlled modulations of neural activity and related behavior.

neuroscience↗

bioRxiv2019

Manipulation of Oscillatory Phase by Transcranial Alternating Current Stimulation

BackgroundOscillatory phase has been proposed as a key parameter defining the spatiotemporal structure of neural activity. To enhance our understanding of brain rhythms and improve clinical outcomes in pathological conditions, phase-specific modulation of oscillations by transcranial alternating current stimulation (tACS) emerged as a promising approach. However, the effectiveness of tACS in humans is still critically debated. ObjectiveHere, we investigated the phase-specificity of tACS effects on visually evoked steady state responses (SSRs) in 24 healthy human participants of either sex. MethodsTo this end, we used an intermittent electrical stimulation protocol and assessed the influence of tACS on SSR amplitude in the interval immediately following tACS. ResultsWe observed that the phase shift between flicker and tACS modulates evoked SSR amplitudes. The tACS effect size was dependent on the strength of flicker-evoked oscillatory activity, with larger effects in participants showing weaker locking of neural responses to flicker phase. Neural sources of phase-specific effects were localized in the parieto-occipital cortex within flicker-entrained regions. Importantly, the optimal phase shift between flicker and tACS associated with strongest SSRs was correlated with cortical SSR onset delays over the visual cortex. ConclusionsOverall, our data provide electrophysiological evidence for phase-specific modulations of oscillatory activity by tACS in humans. As the optimal timing of tACS application was dependent on neural conduction times as measured by SSR onset delays, data suggest that the interaction between tACS effect and SSR was cortical in nature. These findings corroborate the physiological efficacy of tACS and highlight its potential for controlled modulations of brain signals.

neuroscience↗