Biology subjects

Heida, T.

Publications and source records attributed to Heida, T..

3 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

Weak electric fields of deep brain stimulation can entrain spiking in multi-compartment cortical neuron models

Background: Deep brain stimulation (DBS) is widely used to treat neurological disorders, but how it exerts its therapeutic effects remains an open question. Although DBS primarily acts through stimulated subcortical structures and their networks, recent studies have demonstrated that cortical electric field (E-field) strengths generated during DBS are comparable to, and can exceed, those shown to modulate neuronal activity with transcranial alternating current stimulation. We therefore investigated whether and how these weak DBS fields can directly modulate cortical spike timing. Methods: We used multi-compartment computational models of five neuron types across all cortical layers and exposed them to E-fields modeled as DBS pulses. E-field amplitudes spanned the typical range of cortical E-field strengths during DBS, while frequency and orientation were varied. Entrainment was assessed using peri-stimulus time histograms and quantified by the phase locking value (PLV). Results: Weak DBS fields modulated spike timing of some neurons by either increasing or decreasing the likelihood of firing immediately following the stimulation pulse. This modulation reflected entrainment to the stimulation, with the PLV increasing with E-field amplitude and frequency. The magnitude and direction of spike-timing modulation varied across neuron types and depended on the orientation of the field. Conclusion: These findings suggest that cortical E-fields of DBS may directly influence activity of some cortical neurons, alongside the established indirect cortical effects mediated by subcortical targets and their networks. This provides a new perspective on how DBS may influence cortical activity and offers insights into its potential mechanisms of therapeutic and/or side effects.

neuroscience↗

bioRxiv2018

Standardized microgel beads as elastic cell mechanical probes

Cell mechanical measurements are gaining increasing interest in biological and biomedical studies. However, there are no standardized calibration particles available that permit the cross-comparison of different measurement techniques operating at different stresses and time-scales. Here we present the rational design, production, and comprehensive characterization of poly-acylamide (PAAm) microgel beads mimicking biological cells. We produced mono-disperse beads at rates of 20 - 60 kHz by means of a microfluidic droplet generator, where the pre-gel composition was adjusted to tune the beads elasticity in the range of cell and tissue relevant mechanical properties. We verified bead homogeneity by optical diffraction tomography and Brillouin microscopy. Consistent elastic behavior of microgel beads at different shear rates was confirmed by AFM-enabled nanoindentation and real-time deformability cytometry (RT-DC). The remaining inherent variability in elastic modulus was rationalized using polymer theory and effectively reduced by sorting based on forward-scattering using conventional flow cytometry. Our results show that PAAm microgel beads can be standardized as mechanical probes, to serve not only for validation and calibration of cell mechanical measurements, but also as cell-scale stress sensors.\n\nSignificance StatementOften vastly different cell mechanical properties are reported even for the same cell type when employing different measurement techniques. This discrepancy shows the urgent need for standardized calibration particles to cross-compare and validate techniques. Microgel beads can serve this purpose, but they have to fulfil specific requirements such as homogeneity, sizes and elasticities in the range of the cells, and they have to provide comparable results independent of the method applied. Here we demonstrate the standardized production of polyacrylamide microgel beads with all the features an elastic cell-mimic should have. These can not only be used as method calibration particles, but can also serve as cell-scale sensors to quantify normal and shear stresses exerted by other cells and inside tissues, enabling many new applications.

biophysics↗