Biology subjects

Van Hoornweder, S.

Publications and source records attributed to Van Hoornweder, S..

8 recordsLinked to original sources

bioRxiv2026

Opposing modulation of cortical and corticospinal excitability across movement-related beta stages

Discrete voluntary movement depends on rapid changes in neural excitability across cortical and corticospinal circuits, yet how intrinsic movement-related neural states shape multi-level excitability remains unclear. Here, we combined individualized, state-targeted transcranial magnetic stimulation (TMS) with electroencephalography and electromyography recordings during visually cued finger movements to probe excitability across movement-related beta-band dynamics during two complementary experiments. Immediate transsynaptic cortical excitability closely tracked intrinsic beta dynamics, with attenuation of the second immediate TMS-evoked potential during beta desynchronization and recovery during the post-movement beta rebound. In contrast, corticospinal excitability showed the opposite pattern, with larger motor-evoked potentials during beta desynchronization and reduced responses during beta rebound. Together, these findings identify endogenous beta-state dynamics as a key regulator of movement-related cortical excitability and reveal a fundamental dissociation between how intrinsic brain activity tunes local cortical excitability and corticospinal output in humans.

neuroscience↗

bioRxiv2026

Resting-state and task-related neurometabolite levels differentially relate to cortical excitability in the sensorimotor and prefrontal cortex

BackgroundNormal brain function requires a dynamic balance between inhibition and excitation. While magnetic resonance spectroscopy (MRS) quantifies the chief inhibitory and excitatory neurometabolites, GABA and glutamate-glutamine (Glx), the combination of transcranial magnetic stimulation and electroencephalography (TMS-EEG) provides a complementary measure of cortical inhibition-excitation dynamics via transcranial evoked potentials (TEPs). However, the relationship between neurometabolite concentrations and TEPs is unclear. ObjectiveTo characterize the relationship between neurometabolite concentrations and TEPs, as a function of TEP component, TMS pulse type, brain region, neurometabolite, and MRS brain state. MethodsTwenty-five young healthy adults completed a 4-day protocol. Sessions 1 and 2 involved screening, anatomical MRI, and functional MRI localization of DLPFC. In session 3, single- and paired-pulse TMS-EEG were applied over SM1 and DLPFC. Session 4 included resting-state and motor-task-related MRS of SM1 and DLPFC. ResultsIn SM1, task-related GABAergic tone strongly predicted early to mid-latency TEPs. In DLPFC, local early to mid-latency TEPs showed no relationship to neurometabolites, whereas late and global TEP outcomes revealed some links. The later N100 TEP was the only component consistently modulated by paired-pulse TMS. Task-related MRS measures consistently outperformed resting-state measures in predicting TEPs for SM1, while the opposite was true for DLPFC. ConclusionsSingle-pulse TEPs reliably index the local inhibitory tone in SM1, with limited added value from paired-pulse paradigms. These findings support the use of single-pulse TEPs as accessible markers of cortical inhibition, especially for SM1, and may inform biomarkers and strategies for individualized neuromodulation. Key point summaryO_LINormal brain function relies on a balance between inhibition and excitation, yet the relationship between local cortical neurometabolite levels and cortical excitability in humans remains poorly understood. C_LIO_LIWe measured inhibitory and excitatory neurometabolites using magnetic resonance spectroscopy and assessed cortical excitability responses to non-invasive stimulation using combined transcranial magnetic stimulation - electroencephalography (TMS-EEG). C_LIO_LIIn the primary sensorimotor cortex (SM1), local cortical responses to stimulation were best explained by inhibitory GABA levels during motor task performance. In the dorsolateral prefrontal cortex (DLPFC), global cortical responses were best predicted by resting-state neurometabolite levels. C_LIO_LIOverall, paired-pulse TMS paradigms offered little additional value over single-pulse paradigms for informing on neurometabolite levels. C_LIO_LIBy demonstrating region- and state-dependent links between neurometabolite levels and cortical excitability, our findings position TMS-EEG as an accessible biomarker of cortical inhibition, particularly in SM1. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=79 SRC="FIGDIR/small/701225v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@132b3faorg.highwire.dtl.DTLVardef@1c5ebeeorg.highwire.dtl.DTLVardef@1048a75org.highwire.dtl.DTLVardef@11e1a4f_HPS_FORMAT_FIGEXP M_FIG C_FIG Abstract figure legendThe left panel provides a stepwise overview of the study protocol, including (i) participant screening, (ii) functional and anatomical magnetic resonance imaging (MRI) scanning for individualization purposes, (iii) single- and paired-pulse transcranial magnetic stimulation-electroencephalography (TMS-EEG), and (iv) magnetic resonance spectroscopy (MRS) acquired at rest and during a bimanual motor task. The middle and right panels show the grand-average EEG responses to single-pulse TMS over the sensorimotor cortex (SM1, red) and dorsolateral prefrontal cortex (DLPFC, blue), respectively. The topographical maps below each EEG response depict the averaged scalp distributions corresponding to each canonical transcranial evoked potential. Per region, the top left illustration shows the group-level MRS voxel placement, whereas the top right illustration shows the simulated TMS-induced electric fields. While early to mid-latency local cortical responses were best predicted by task-related GABAergic inhibition in SM1, global cortical responses following DLPFC stimulation were best predicted by resting-state neurometabolite levels.

neuroscience↗

bioRxiv2025

Not two sides of the same coin: Divergent effects of motor state on corticospinal and cortical responses to TMS of motor cortex

BackgroundTranscranial magnetic stimulation (TMS) of the motor cortex can elicit motor evoked potentials (MEPs) in target muscles, reflecting corticospinal excitability. MEP amplitudes increase with TMS intensity and can be facilitated by tonic muscle pre-activation. Since conventional transcranial evoked potentials (TEPs) also grow with increasing TMS intensity, cortical and corticospinal responses are often considered two facets of the same process. If this were true, changes in physiological motor state should modulate TEPs and MEPs in a similar manner. MethodsTo compare the state-dependency of cortical and corticospinal responses to single-pulse TMS, we simultaneously recorded TEPs and MEPs in 16 healthy young adults during relaxation and isometric contraction of the right first dorsal interosseous (FDI) muscle. For each condition, 100 biphasic TMS pulses were delivered to the left primary motor hand area at five different intensities centered around the resting motor threshold. ResultsTEP and MEP amplitudes increased with stimulation intensity. As predicted, tonic muscle contraction consistently facilitated MEP. On the contrary, muscle contraction attenuated two key peaks of the TEP (N15 and N100). The state-dependent effects of corticospinal and cortical responses were not correlated. DiscussionBoth TEPs and MEPs are reliably modulated by motor state, yet they differ in direction and their magnitudes do not scale with each other. These findings challenge the assumption that cortical and corticospinal responses are two aspects of the same process. MEP facilitation during contraction likely reflects increased spinal excitability, whereas TEP attenuation may reflect reduced responsiveness of cortico-cortical or cortico-subcortical networks.

neuroscience↗

bioRxiv2024

The Causal Role Of Beta Band Desynchronization: Individualized High-Definition Transcranial Alternating Current Stimulation Improves Bimanual Motor Control

ObjectiveTo unveil if 3 mA peak-to-peak high-definition {beta} transcranial alternating current stimulation (tACS) applied over C4 -the area overlaying the right sensorimotor cortex- enhances bimanual motor control and affects movement-related {beta} desynchronization (MR{beta}D), thereby providing causal evidence for the polymorphic role of MR{beta}D in motor control. MethodsIn this sham-controlled, crossover study, 36 participants underwent 20 minutes of fixed 20 Hz tACS; tACS individualized to peak {beta} activity during motor planning at baseline; and sham tACS randomized over three consecutive days. Before, during, and after tACS, participants performed a bimanual tracking task (BTT) and 64-channel electroencephalography (EEG) data was measured. Spatiotemporal and temporal clustering statistics with underlying linear mixed effect models were used to test our hypotheses. ResultsIndividualized tACS significantly improved bimanual motor control, both online and offline, and increased online MR{beta}D during motor planning compared to fixed tACS. No offline effects of fixed and individualized tACS on MR{beta}D were found compared to sham, although tACS effects did trend towards the hypothesized MR{beta}D increase. Throughout the course of the study, MR{beta}D and bimanual motor performance improved. Exclusively during motor planning, MR{beta}D was positively associated to bimanual motor performance improvements, emphasizing the functionally polymorphic role of MR{beta}D. tACS was well tolerated and no side-effects occurred. ConclusionIndividualized {beta}-tACS improves bimanual motor control and enhances motor planning MR{beta}D online. These findings provide causal evidence for the importance of MR{beta}D when planning complex motor behavior.

neuroscience↗

bioRxiv2024

Head And Shoulders - The Impact Of An Extended Head Model On The Simulation And Optimization Of Transcranial Electric Stimulation

Electric field calculations are increasingly used for dose characterization of transcranial electrical stimulation (tES), but existing open-source head models are inaccurate for extracephalic montages that include electrodes placed on the neck or shoulder. We introduce the "Ernie Extended" model, an MRI- and CT-derived open-source head model extending to the upper shoulder region. Simulations of extracephalic tES targeting the cerebellum and supplementary motor area show significant differences in electric fields when using Ernie Extended compared to the non-extended Ernie model. Additionally, we propose an electrode layout that complements the electroencephalography 10- 20 system with extracephalic electrode positions. We demonstrate the use of this layout for optimizing multi-electrode tES montages for cerebellar stimulation, enhancing focality and reducing off-target stimulation, particularly of the spinal cord. Our results highlight the practical value of the Ernie Extended model for accurately characterizing doses produced by extracephalic tES montages and when targeting more caudal brain regions.

neuroscience↗

bioRxiv2023

The effects of prefrontal tDCS on working memory associate with the magnitude of the individual electric field in the brain

Transcranial direct current stimulation (tDCS) over the prefrontal cortex has the potential to enhance working memory by means of a weak direct current applied to the scalp. However, its effects are highly variable and possibly dependent on individual variability in cortical architecture and head anatomy. Unveiling sources of heterogeneity might improve fundamental and clinical application of tDCS in the field. Therefore, we investigated sources of tDCS variability of prefrontal 1.5mA tDCS, 3mA tDCS and sham tDCS in 40 participants (67.5% women, mean age 24.7 years) by associating simulated electric field (E-field) magnitude in brain regions of interest (dorsolateral prefrontal cortex, anterior cingulate cortex (ACC) and subgenual ACC) and working memory performance. Emotional and non-emotional 3-back paradigms were used. In the tDCS protocol analysis, effects were only significant for the 3mA group, and only for the emotional tasks. In the individual E-field magnitude analysis, faster responses in non-emotional, but not in the emotional task, were associated with stronger E-fields in all brain regions of interest. A follow-up analysis showed that people with higher (vs. lower) E-fields magnitude in the left DLPFC were faster in the both tasks, and more accurate in the emotional task. Concluding, individual E-field distribution might explain part of the variability of prefrontal tDCS effects on working memory performance and in clinical samples. Our results suggest that tDCS effects can be more consistent or improved by applying personalizing current intensity, although this hypothesis should be confirmed by further studies.

neuroscience↗

bioRxiv2023

From scalp to cortex, the whole isn't greater than the sum of its parts: introducing GetTissueThickness (GTT) to assess age and sex differences in tissue thicknesses

Noninvasive techniques to record and stimulate the brain rely on passing through the tissues in between the scalp and cortex. Currently, there is no method to obtain detailed information about these scalp-to-cortex distance (SCD) tissues. We introduce GetTissueThickness (GTT), an open-source, automated approach to quantify SCD, and unveil how tissue thicknesses differ across age groups, sexes and brain regions (n = 250). We show that men have larger SCD in lower scalp regions and women have similar-to-larger SCD in regions closer to the vertex, with aging resulting in increased SCD in fronto-central regions. Soft tissue thickness varies by sex and age, with thicker layers and greater age-related decreases in men. Compact and spongy bone thickness also differ across sexes and age groups, with thicker compact bone in women in both age groups and an age-related thickening. Older men generally have the thickest cerebrospinal fluid layer and younger women and men having similar cerebrospinal fluid layers. Aging mostly results in grey matter thinning. Concerning SCD, the whole isnt greater than the sum of its parts. GTT enables rapid quantification of the SCD tissues. The distinctive sensitivity of noninvasive recording and stimulation modalities to different tissues underscores the relevance of GTT.

neuroscience↗

bioRxiv2023

A Systematic Review and Large-Scale tES and TMS Electric Field Modeling Study Reveals How Outcome Measure Selection Alters Results in a Person- and Montage-Specific Manner

BackgroundElectric field (E-field) modeling is a potent tool to examine the cortical effects of transcranial magnetic and electrical stimulation (TMS and tES, respectively) and to address the high variability in efficacy observed in the literature. However, outcome measures used to report E-field magnitude vary considerably and have not yet been compared in detail. ObjectivesThe goal of this two-part study, encompassing a systematic review and modeling experiment, was to provide an overview of the different outcome measures used to report the magnitude of tES and TMS E-fields, and to conduct a direct comparison of these measures across different stimulation montages. MethodsThree electronic databases were searched for tES and/or TMS studies reporting E-field magnitude. We extracted and discussed outcome measures in studies meeting the inclusion criteria. Additionally, outcome measures were compared via models of four common tES and two TMS modalities in 100 healthy younger adults. ResultsIn the systematic review, we included 118 studies using 151 outcome measures related to E-field magnitude. Structural and spherical regions of interest (ROI) analyses and percentile-based whole-brain analyses were used most often. In the modeling analyses, we found that there was an average of only 6% overlap between ROI and percentile-based whole-brain analyses in the investigated volumes within the same person. The overlap between ROI and whole-brain percentiles was montage- and person-specific, with more focal montages such as 4x1 and APPS-tES, and figure-of-eight TMS showing up to 73%, 60%, and 52% overlap between ROI and percentile approaches respectively. However, even in these cases, 27% or more of the analyzed volume still differed between outcome measures in every analyses. ConclusionsThe choice of outcome measures meaningfully alters the interpretation of tES and TMS E-field models. Well-considered outcome measure selection is imperative for accurate interpretation of results, valid between-study comparisons, and depends on stimulation focality and study goals. We formulated four recommendations to increase the quality and rigor of E-field modeling outcome measures. With these data and recommendations, we hope to guide future studies towards informed outcome measure selection, and improve the comparability of studies.

neuroscience↗