Biology subjects

Baechinger, M.

Publications and source records attributed to Baechinger, M..

10 recordsLinked to original sources

bioRxiv2026

Reward Reduces Motor Fatigability by Increasing Movement Vigour

Reward can enhance motor performance. However, its potential to counteract motor fatigability, a reduction in motor performance during sustained movements, remains underinvestigated. This could be particularly relevant in neurological conditions such as multiple sclerosis, where increased motor fatigability is a prominent symptom. One form of motor fatigability is motor slowing, a decline in movement speed over time evoked by fast, repetitive movements. In this study, we investigated whether the possibility to earn reward attenuates motor slowing, and examined associated changes in muscle activity and pupil size, a putative marker of physical effort. Participants performed a wrist tapping task at maximal voluntary speed with or without the possibility of earning a reward. We found that wrist tapping induced motor slowing and that slowing was significantly reduced by reward. Over time, tapping became more costly as indicated by higher muscle activity and coactivation per tap. This was accompanied by a sustained pupil dilation, which could not solely be explained by tapping speed. These findings suggest that, rather than restoring efficient motor control, reward attenuates motor slowing by allowing participants to access a performance reserve and invest more resources into the task, reflected by increased muscle activation per tap and sustained pupil dilation.

neuroscience↗

bioRxiv2022

Contrast detection is enhanced by non-stochastic, high-frequency transcranial alternating current stimulation with triangle and sine waveform.

Stochastic Resonance (SR) describes a phenomenon where an additive noise (stochastic carrier-wave) enhances the signal transmission in a nonlinear system. In the nervous system, nonlinear properties are present from the level of single ion channels all the way to perception and appear to support the emergence of SR. For example, SR has been repeatedly demonstrated for visual detection tasks, also by adding noise directly to cortical areas via transcranial random noise stimulation (tRNS). We mathematically show that high-frequency, non-stochastic, periodic signals can yield resonance-like effects with linear transfer and infinite signal-to-noise ratio at the output. Here we tested this prediction empirically and investigated whether non-random, high-frequency, transcranial alternating current stimulation (hf-tACS) applied to visual cortex could induce resonance-like effects and enhance performance on a visual detection task. We demonstrated in 28 participants that applying 80 Hz triangular-waves or sine-waves with hf-tACS reduced visual contrast detection threshold for optimal brain stimulation intensities. The influence of hf-tACS on contrast sensitivity was equally effective to tRNS-induced modulation, demonstrating that both hf-tACS and tRNS can reduce contrast detection thresholds. Our findings suggest that a resonance-like mechanism can also emerge when non-stochastic electrical waveforms are applied via hf-tACS. New & NoteworthyOur findings extend our understanding of neuromodulation induced by noninvasive electrical stimulation. We provide first evidence showing acute online benefits of hf-tACStriangle and hf-tACSsine targeting the primary visual cortex (V1) on visual contrast detection in accordance with the resonance-like phenomenon. The non-stochastic hf-tACS and stochastic hf-tRNS are equally effective in enhancing visual contrast detection.

neuroscience↗

bioRxiv2022

Through the eye to the brain: Modulating LC-mediated arousal via pupil-based neurofeedback

The brains arousal state is controlled by several neuromodulatory nuclei known to substantially influence cognition and mental well-being. Here, we investigate whether human participants can gain volitional control of their arousal state using a pupil-based biofeedback approach. Our approach inverts a mechanism suggested by previous literature that links activity of the locus coeruleus (LC), one of the key regulators of central arousal, and pupil dynamics. We show that pupil-based biofeedback enables participants to acquire volitional control of pupil size. Applying pupil self-regulation systematically modulates activity of the LC and other brainstem structures involved in arousal control. Further, it modulates cardiovascular measures such as heart rate, and behavioural and psychophysiological responses during an oddball task. We provide evidence that pupil-based biofeedback makes the brains arousal system accessible to volitional control, a finding that has tremendous potential for translation to behavioral and clinical applications across various domains, including stress-related and anxiety disorders.

neuroscience↗

bioRxiv2022

Transcranial random noise stimulation of the primary visual cortex but not retina modulates visual contrast sensitivity.

Transcranial random noise stimulation (tRNS) has been shown to significantly improve visual perception. Previous studies demonstrated that tRNS delivered over cortical areas acutely enhances visual contrast detection of stimuli when tRNS intensity is optimized for the individual. However, it is currently unknown whether tRNS-induced signal enhancement could be achieved within different neural substrates along the retino-cortical pathway and whether the beneficial effect of optimal tRNS intensities can be reproduced across sessions. In 3 experimental sessions, we tested whether tRNS applied to the primary visual cortex (V1) and/or to the retina improves visual contrast detection. We first measured visual contrast detection threshold (VCT; N=24, 16 females) during tRNS delivery separately over V1 (no tRNS, 0.75, 1, 1.5mA) and over the retina (no tRNS, 0.1, 0.2, 0.3mA), determined the optimal tRNS intensities for each individual (ind-tRNS), and retested the effects of ind-tRNS within the sessions. We further investigated whether we could reproduce the ind-tRNS-induced modulation on a different session (N=19, 14 females). Finally, we tested whether the simultaneous application of ind-tRNS to the retina and V1 causes additive effects. We found that at the group level tRNS of 0.75mA decreases VCT compared to baseline when delivered to the V1. Beneficial effects of ind-tRNS could be replicated when retested within the same experimental session but not when retested in a separate session. Applying tRNS to the retina did not cause a systematic reduction of VCT, irrespective of whether the individually optimized intensity was considered or not. We also did not observe consistent additive effects of V1 and retina stimulation. Our findings demonstrate that V1 seems to be more sensitive than the retina to tRNS-induced modulation of visual contrast processing. Significance statementOur findings confirm previous evidence showing acute online benefits of tRNS of V1 on visual contrast detection in accordance with the stochastic resonance phenomenon. We further extend it, demonstrating that the optimal tRNS intensity varies among participants, but when individually tailored it can improve visual processing when re-tested within the experimental session. The tRNS-induced enhancement in visual sensitivity seems to be specific for cortical contrast processing as stimulation of the retina did not lead to systematic effects.

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bioRxiv2020

Transcranial Random Noise Stimulation acutely lowers the response threshold of human motor circuits

AO_SCPLOWBSTRACTC_SCPLOWTranscranial random noise stimulation (tRNS) over cortical areas has been shown to acutely improve performance in sensory detection tasks. One explanation for this behavioural effect is stochastic resonance, a mechanism that explains how signal processing in non-linear systems can benefit from added noise. While acute noise benefits of electrical random noise stimulation have been demonstrated at the behavioural level as well as in in vitro preparations of neural tissue, it is currently largely unknown whether similar effects can be shown at the neural population level using neurophysiological readouts of human cortex. Here we hypothesized that acute tRNS will increase the responsiveness of primary motor cortex (M1) when probed with transcranial magnetic stimulation. Neural responsiveness was operationalized via the well-known concept of the resting motor threshold (RMT). We showed that tRNS acutely decreases RMT. This effect was small, but it was consistently replicated across four experiments including different cohorts (total N=81, 46 females, 35 males), two tRNS electrode montages, and different control conditions. Our experiments provide critical neurophysiological evidence that tRNS can acutely generate noise benefits by enhancing the neural population response of human M1. SO_SCPLOWIGNIFICANCEC_SCPLOWO_SCPCAP C_SCPCAPO_SCPLOWSTATEMENTC_SCPLOWA hallmark feature of stochastic resonance is that signal processing can benefit from added noise. This has mainly been demonstrated at the single-cell level in vitro where the neural response to weak input signals can be enhanced by simultaneously applying random noise. Our finding that tRNS acutely increases the excitability of corticomotor circuits extends the principle of noise benefits to the neural population level in human cortex. Our finding is in line with the notion that tRNS might affect cortical processing via the stochastic resonance phenomenon. It suggests that enhancing the response of cortical populations to an external stimulus might be one neurophysiological mechanism mediating performance improvements when tRNS is applied to sensory cortex during perception tasks.

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bioRxiv2020

No modulatory effect of rhythmic visual alpha/gamma stimulation in a bistable motion illusion

The motion quartet, also called stroboscopic alternative motion (SAM), is a bistable apparent motion paradigm where dots are perceived as moving either horizontally or vertically. These two percepts are known to switch randomly depending on both alpha (8 - 12 Hz) and gamma (30 - 80 Hz) oscillations within and between hemispheres, respectively. However, whether these oscillations play a causal role in triggering perceptual switches remains unknown. Here, we aimed to entrain brain oscillations in the visual system by presenting flickering stimuli. Two LEDs were flickering either at 10 Hz, 40 Hz or corresponding jittered stimulation frequencies on the left and right sides of the visual field during the presentation of a motion quartet. In our control condition (no stimulation), we show that interhemispheric gamma connectivity (spectral coherence) between the visual cortices of both hemispheres is important for sensory feature integration. On the other hand, alpha power did not predict perceptual switches for the motion quartet. Rhythmic visual stimulation with 10 Hz and 40 Hz evoked resonance-like neural responses but did not alter visual perception. Thus, although sensory stimuli seem to entrain ongoing brain rhythms, the effect on human behavior differs from the principles observed for endogenous brain oscillations.

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bioRxiv2019

Modulation of tactile detection threshold with rhythmic somatosensory entrainment

Ongoing neural activity in human somatosensory cortex has a strong impact on the detectability of weak tactile stimuli. Recent studies suggest that brain oscillations, which determine the state of excitability of a cortical area, play a crucial role in this process. Mainly two frequency bands have been reported to be involved in conscious sensory perception: alpha (8 - 12 Hz) and beta (15 - 30 Hz). In addition to correlative findings, more recent studies investigated causality by measuring the extent to which directly modulating brain oscillations affects sensory perception. While most of these studies use transcranial alternating current stimulation (tACS), rhythmic sensory stimulation has been suggested as a simple and safe alternative to entrain ongoing neural activity. However, convincing findings demonstrating the modulation of neural signals and related behavioral function are scarce.\n\nHere, we investigated whether rhythmically induced brain oscillations by means of vibrotactile stimulation (i.e. sensory entrainment) modulate tactile detection. In line with previous findings, we show in trials without sensory entrainment that preceding alpha power and phase-angles in beta oscillations predict the detection rate of a weak tactile stimulus. Further, we reveal a masking effect induced by sensory entrainment stimulation resulting in higher perception thresholds. Intriguingly, we find that the masking effect is modulated by the strength of neural entrainment resulting from 20 Hz stimulation. Our data provide evidence for the possibility to modulate sensory processing with rhythmic sensory stimulation. However, in light of the induced masking effects, the feasibility of this entrainment method to modulate human behavior remains questionable.

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bioRxiv2019

Steady-state responses in the somatosensory system interact with endogenous beta activity

Brain oscillations have been related to many aspects of human behavior. To understand a potential causal relationship, it is of great importance to develop methods for modulating ongoing neural activity. It has been shown that external rhythmic stimulation leads to an oscillatory brain response that follows the temporal structure of the presented stimulus and is assumed to reflect the synchronization of ongoing neural oscillations with the stimulation rhythm. This interaction between individual brain activity and so called steady-state evoked potentials (SSEPs) is the fundamental requirement of neural entrainment. Here, we investigate whether neural responses to rhythmic vibrotactile stimulation, measured with EEG, are dependent on ongoing individual brain oscillations, and therefore reflect entrained oscillatory activity. For this, we measured phase synchronization in response to rhythmic stimulation across various frequencies in the alpha and beta band. Three different stimulation intensities were applied for each frequency relative to the individual sensory threshold. We found that a higher stimulation intensity, compared to lower intensities, resulted in a more pronounced phase synchronization with the stimulation signal. Moreover, EEG responses to low stimulation frequencies closer to individual beta peak frequencies revealed a higher degree of entrainment, compared to stimulation conditions with frequencies that were more distant to endogenous oscillations. Our findings provide evidence that the efficacy of vibrotactile rhythmic beta stimulation to evoke a SSEPs is dependent on ongoing brain oscillations.

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bioRxiv2019

Motor fatigability as evoked by repetitive movements results from a gradual breakdown of surround inhibition

Motor fatigability emerges when demanding tasks are executed over an extended period of time. Here, we used repetitive low-force movements that cause a gradual reduction in movement speed (or \"motor slowing\") to study the central component of fatigability in healthy adults. We show that motor slowing is associated with a gradual increase of net excitability in the motor network and, specifically, in primary motor cortex (M1), which results from overall disinhibition. Importantly, we link performance decrements to a breakdown of surround inhibition in M1, which is associated with high coactivation of antagonistic muscle groups. This is consistent with the model that a loss of inhibitory control might broaden the tuning of population vectors such that movement patterns become more variable, ill-timed and effortful. We propose that the release of inhibition in M1 is an important mechanism underpinning motor fatigability and, potentially, also pathological fatigue as frequently observed in patients with brain disorders.

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bioRxiv2017

Concurrent tACS-fMRI Reveals Causal Influence Of Power Synchronized Neural Activity On Resting State fMRI Connectivity

Resting state fMRI (rs-fMRI) is commonly used to study the brains intrinsic neural coupling, which reveals specific spatiotemporal patterns in the form of resting state networks (RSN). It has been hypothesized that slow rs-fMRI oscillations (<0.1 Hz) are driven by underlying electrophysiological rhythms that typically occur at much faster timescales (>5 Hz); however, causal evidence for this relationship is currently lacking. Here we measured rs-fMRI in humans while applying transcranial alternating current stimulation (tACS) to entrain brain rhythms in left and right sensorimotor cortices.\n\nThe two driving tACS signals were tailored to the individuals alpha rhythm (8-12 Hz) and fluctuated in amplitude according to a 1 Hz power envelope. We entrained the left versus right hemisphere in accordance to two different coupling modes where either alpha oscillations were synchronized between hemispheres (phase-synchronized tACS) or the slower oscillating power envelopes (power-synchronized tACS).\n\nPower-synchronized tACS significantly increased rs-fMRI connectivity within the stimulated RSN compared to phase-synchronized or no tACS. This effect outlasted the stimulation period and tended to be more effective in individuals who exhibited a naturally weak interhemispheric coupling. Using this novel approach, our data provide causal evidence that synchronized power fluctuations contribute to the formation of fMRI-based RSNs. Moreover, our findings demonstrate that the brains intrinsic coupling at rest can be selectively modulated by choosing appropriate tACS signals, which could lead to new interventions for patients with altered rs-fMRI connectivity.\n\nSignificance StatementResting state fMRI has become an important tool to estimate brain connectivity. However, relatively little is known about how slow hemodynamic oscillations measured with fMRI relate to electrophysiological processes.\n\nIt was suggested that slowly fluctuating power envelopes of electrophysiological signals synchronize across brain areas and that the topography of this activity is spatially correlated to resting state networks derived from rs-fMRI. Here we take a novel approach to address this problem and establish a causal link between the power fluctuations of electrophysiological signals and rs-fMRI via a new neuromodulation paradigm, which exploits these power-synchronization mechanisms.\n\nThese novel mechanistic insights bridge different scientific domains and are of broad interest to researchers in the fields of Medical Imaging, Neuroscience, Physiology and Psychology.

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