Biology subjects

Stecher, H. I.

Publications and source records attributed to Stecher, H. I..

3 recordsLinked to original sources

bioRxiv2026

Effect of stimulation parameters for transcranial temporal interference stimulation to enhance occipital alpha-oscillations in healthy participants

Transcranial temporal interference stimulation (tTIS) has recently emerged as a non-invasive method for modulating neural activity using interfering high-frequency electric fields. Although behavioral and neuroimaging effects of tTIS have been reported, evidence for electrophysiological modulation remains inconsistent, and it is unclear whether observed effects are attributable to temporal interference itself or to other components of the signal, e.g. high-frequency carrier signals. We therefore investigated whether tTIS at to the individual alpha frequency (IAF) modulates occipital alpha power compared with both sham stimulation and an active high-frequency carrier control. Eighteen healthy participants were enrolled in a randomized, double-blind, within-subject crossover study; 17 participants were included in the final analysis. Each participant completed three stimulation sessions consisting of three conditions (tTIS, carrier control, sham stimulation). tTIS was delivered for 20 minutes using two high-frequency signals at 1000 Hz and 1000 Hz + IAF, whereas the carrier control used two 1000-Hz signals without an envelope modulation. EEG was recorded before and after stimulation during a visual vigilance task. Individual electric-field distributions in the occipital cortex were estimated using structural MRI-based finite-element simulations. A significant main effect of stimulation condition on the change in occipital alpha power was observed (F(2,32) = 5.69, p = .008, eta2p = .26). Post-hoc comparisons showed a significantly greater increase in alpha power following tTIS compared with both the carrier control (mean difference = 0.30, adjusted p = .036, Cohens d = 0.686) and sham stimulation (mean difference = 0.31, adjusted p = .037, Cohens d = 0.683). Carrier and sham conditions did not differ (adjusted p = 1.000). No behavioral effects were observed. The magnitude of the alpha-power change was not significantly associated with simulated electric-field strength in the occipital target region. tTIS was well tolerated, with no stimulation-related study discontinuations. tTIS targeting the occipital cortex therefore produced significant post-stimulation enhancement of alpha power beyond both sham and high-frequency carrier stimulation. The absence of an effect in the carrier condition supports the interpretation that the electrophysiological aftereffect depends on temporal interference rather than high-frequency stimulation components alone. These findings provide evidence for frequency-specific modulation of cortical oscillations by tTIS and support further investigation of its underlying mechanisms and stimulation parameters.

neuroscience↗

bioRxiv2025

In-ear-tACS: Auditory Perception and Side Effects depend on Electrode Montage, Frequency, and DC-Offset

BackgroundNon-invasive transcranial alternating current stimulation (tACS) of the cochlea might be a promising new therapeutic option for patients with chronic tinnitus. However, electric stimulation of small, sensitive target regions, such as the inner ear, can cause adverse side effects (SEs). ObjectiveTo identify stimulation parameters with low side-effect profiles while reliably stimulating the cochlea, thereby improving patient comfort and safety and paving the way for the development of a medical device for treating patients with chronic tinnitus. ApproachHearing-healthy participants were stimulated with electrodes in the ear canal. Stimulation of the cochlea elicits a soft hearing impression (HI) in participants, indicating successful stimulation of the early auditory pathway. We systematically compare HS and SEs across distinct electrode configurations and stimulation parameters, including stimulation frequency and the presence of a Direct Current (DC)-offset. We record SE occurrence via visual analog scales after stimulation. Main ResultsWe find that tACS stimulation between 250 Hz and 2000 Hz reliably elicits HIs in participants. SEs are generally low. No occurrence of SEs resulted in participant withdrawal or severe adverse events, with only phosphenes, skin tingling, and a sense of vibration being reported as impactful. The addition of a slight DC-offset increases the occurrence and magnitude of SEs considerably. SignificanceOur results demonstrate the feasibility of tACS in non-invasively stimulating the auditory pathway with minimal adverse SE. Stimulation parameters with a low SE profile can be applied in further studies with tinnitus patients.

neuroscience↗

bioRxiv2025

Carbonized rubber electrodes can cause a DC-offset in transcranial alternating current stimulation

IntroductionCarbonized rubber electrodes are widely used in non-invasive brain stimulation studies. Due to their polarizable nature, however, they can cause a voltage offset, which might be problematic for concurrent EEG studies. ObjectiveIn this study, we aim to describe the voltage offset and ensure that the offset does not alter the intended waveform of applied stimulation. MethodsUsing data from 2 human studies and phantom measurements, which employed carbonized rubber electrodes, we quantify the magnitude and frequency of DC-offsets and contrast this against pilot-measurements using Ag/AGCl-electrodes. In a further phantom study, we record the offset-voltage that arises from the electrode/electrolyte interface and compare this to the voltage put out by the stimulation device. ResultsA non-zero voltage offset is present in all human and phantom studies employing carbonized rubber electrodes, while the offset using Ag/AgCl electrodes is close to zero. Direct measurements of the stimulator output in the presence of a measurable voltage offset at the stimulation electrodes shows that the offset originates from the electrodes and not from the current provided by the stimulation device. ConclusionUsing carbonized rubber-electrodes for stimulation can result in the emergence of a measurable voltage offset, due to their polarizable nature. We argue that this offset can be problematic in concurrent EEG recordings, as they pose the risk of amplifier saturation and distortions of the recorded stimulation waveform.

neuroscience↗