Biology subjects

Witt, K.

Publications and source records attributed to Witt, K..

7 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↗

bioRxiv2026

Structural Connectivity Between the Locus Coeruleus and Nucleus Basalis of Meynert Relates to Dual-Task Performance

The noradrenergic locus coeruleus (LC) and the cholinergic nucleus basalis of Meynert (nBM) are key hubs of ascending neuromodulatory systems that shape large-scale brain dynamics. However, the behavioral relevance of the structural and functional connectivity between these nuclei remains poorly understood. Here, we investigated whether LC-nBM structural or functional connectivity is related to cognitive-motor dual-task performance in healthy younger and older adults. Fifty-four participants (36 older, 18 younger) underwent diffusion MRI, resting-state fMRI, and behavioral assessment using an MRI-compatible cognitive-motor dual-task paradigm. LC-nBM structural connectivity was estimated using tractography, whereas resting-state functional connectivity was quantified as Fisher z-transformed correlations between LC and nBM time series. LC-nBM structural connectivity was better explained by a quadratic rather than a linear or cubic age model, indicating non-linear age-related variation, whereas functional connectivity showed no significant age-related association. Higher LC-nBM structural connectivity was associated with greater cognitive dual-task cost, but not with motor dual-task cost or single- or dual-task reaction times. This association was not moderated by age group and was not statistically explained by attentional and executive performance as measured by the Test of Attentional Performance. These findings suggest that LC-nBM structural connectivity is selectively associated with cognitive-motor interference, potentially reflecting a neuromodulatory pathway that constrains the balance between task-specific stabilization and flexible cross-domain coordination during a cognitive-motor dual-tasking.

neuroscience↗

bioRxiv2025

Domain-Specific Functional Network Adaptations Supporting Dual-Task Performance in Older Adults

Aging is associated with declines in both motor and cognitive functions, which are well captured by dual-task gait paradigms. However, the functional brain network mechanisms supporting motor and cognitive aspects of dual-task performance in aging remain unclear. We examined 40 older adults (50-80 years) and 20 younger adults (20-40 years) who performed a motor single-task (pedaling), a cognitive single-task (Go/NoGo), and a combined cognitive-motor dual-task during functional magnetic resonance Imaging (fMRI) using a custom-built MRI-compatible pedaling device. Behaviorally, older adults showed significant dual-task costs in motor performance, while cognitive performance was preserved. Neurally, older adults showed selective increases in connectivity within executive and motor-planning regions of cognitive networks, consistent with compensatory recruitment, whereas motor networks underwent broader reorganization, with strengthened frontoparietal control circuits but weakened cerebello-parietal and sensorimotor pathways. Multivariate analyses further revealed age-related differences in latent connectivity- behavior relationships: motor-network patterns in older adults were more dispersed, reflecting heterogeneous reorganization, whereas cognitive-network patterns were more overlapping across groups, suggesting relative preservation. These findings suggest that aging involves a domain-specific balance of resilience and vulnerability across brain networks and highlight motor-network adaption as a promising target for understanding why some older adults maintain function while others decline.

neuroscience↗

bioRxiv2025

Apomorphine susceptibility and prenatal infection alter neurodevelopment, synaptic density and anticipatory behavior in rats

Schizophrenia is a complex psychiatric disorder, driven by genetic and environmental factors. While individual risk genes have limited impact, polygenic susceptibility increases the likelihood of schizophrenia and heightens sensitivity to environmental stressors, such as prenatal immune activation. Yet, preclinical studies often focused on single-gene mutations, leaving polygenic influences largely unexplored. Using the apomorphine-susceptible (APO-SUS) rat model, which exhibits schizophrenia-like features, we investigated how polygenic susceptibility influences early neurodevelopment, synaptic density, and behavior, and how these effects are modulated by prenatal immune activation. APO-SUS rats demonstrated early neurodevelopmental abnormalities, including a reduced number and duration of separation-induced ultrasonic vocalizations (USVs), increased principal frequency of USVs, and reduced heart rate variability (HRV), indicative of heightened sympathetic dominance commonly seen in psychiatric disorders. These effects were particularly pronounced in females. Male APO-SUS rats exhibited elevated synaptophysin levels, a presynaptic marker for synaptic density, in the frontal cortex during adolescence and in the hippocampus during adulthood. Interestingly, prenatal immune activation counteracted some of these changes, preventing HRV reduction and normalizing synaptophysin levels. Male and female APO-SUS rats, as well as Wistar male rats exposed to prenatal immune activation, showed anticipatory behavior during adolescence, but not in adulthood. Our results suggest that polygenic susceptibility induces early neurodevelopmental changes and that genetic and environmental risk factors do not always act synergistically; sometimes counterbalancing each other. Future studies should explore how early neurodevelopmental changes, such as alterations in USVs and HRV, influence later behavioral outcomes in polygenic models of schizophrenia. HighlightsO_LIApomorphine-susceptible rats show altered vocalizations and heart rate variability C_LIO_LIApomorphine susceptibility increases synaptophysin in frontal cortex and hippocampus C_LIO_LIPrenatal immune activation reduces synaptophysin in the adult frontal cortex C_LIO_LIPrenatal immune activation prevents apomorphine-susceptible brain and behavior changes C_LI

animal behavior and cognition↗

bioRxiv2023

Longitudinal Observations of the Effects of Ischemic Stroke on Binaural Perception

Acute ischemic stroke, characterized by a localized reduction in blood flow to specific areas of the brain, has been shown to affect binaural auditory perception. In a previous study conducted during the acute phase of ischemic stroke, two tasks of binaural hearing were performed: binaural tone-in-noise detection, and lateralization of stimuli with interaural time- or level differences (Dietze et al., 2022, Front. Neurosci. 16:1022354). Various lesion-specific, as well as individual, differences in binaural performance between patients in the acute phase of stroke and a control group were demonstrated. For the current study, we re-invited the same group of patients, whereupon a subgroup repeated the experiments during the subacute and chronic phases of stroke. Similar to the initial study, this subgroup consisted of patients with lesions in different locations, including cortical and subcortical areas. At the group level, the results from the tone-in-noise detection experiment remained consistent across the three measurement phases, as did the number of deviations from normal performance in the lateralization task. However, the performance in the lateralization task exhibited variations over time among individual patients. Some patients demonstrated improvements in their lateralization abilities, indicating recovery, whereas others lateralization performance deteriorated during the later stages of stroke. Notably, our analyses did not reveal consistent patterns for patients with similar lesion locations. These findings suggest that recovery processes are more individual than the acute effects of stroke on binaural perception. Individual impairments in binaural hearing abilities after the acute phase of ischemic stroke have been demonstrated and should therefore also be targeted in rehabilitation programs.

neuroscience↗

bioRxiv2020

Replicability, repeatability, and long-term reproducibility of cerebellar morphometry

To identify robust and reproducible methods of cerebellar morphometry that can be used in future large-scale structural MRI studies, we investigated the replicability, repeatability, and longterm reproducibility of three fully-automated software tools: FreeSurfer, CERES, and ACAPULCO. Replicability was defined as computational replicability, determined by comparing two analyses of the same high-resolution MRI data set performed with identical analysis software and computer hardware. Repeatability was determined by comparing the analyses of two MRI scans of the same participant taken during two independent MRI sessions on the same day for the Kirby-21 study. Long-term reproducibility was assessed by analyzing two MRI scans of the same participant in the longitudinal OASIS-2 study. We determined percent difference, the image intraclass correlation coefficient, the coefficient of variation, and the intraclass correlation coefficient between two analyses. Our results show that CERES and ACAPULCO use stochastic algorithms that result in surprisingly high differences between identical analyses for ACAPULCO and small differences for CERES. Changes between two consecutive scans from the Kirby-21 study were less than {+/-}5% in most cases for FreeSurfer and CERES (i.e., demonstrating high repeatability). As expected, long-term reproducibility was lower than repeatability for all software tools. In summary, CERES is an accurate, as demonstrated before, and reproducible tool for fully-automated segmentation and parcellation of the cerebellum. We conclude with recommendations for the assessment of replicability, repeatability, and longterm reproducibility in future studies on cerebellar structure.

neuroscience↗

bioRxiv2019

Model-based and model-free analyses of the neural correlates of tongue movements

The tongue performs movements in all directions to subserve its diverse functions in chewing, swallowing, and speech production. The aims of the present study were twofold: using task-based functional MRI in a group of 17 healthy young participants, we studied (1) potential differences in the cerebral control of frontal, horizontal, and vertical tongue movements and (2) potential inter-individual differences in tongue motor control. To investigate differences between different tongue movements, we performed voxel-wise multiple linear regressions. To investigate inter-individual differences, we applied a novel approach, spatio-temporal filtering of independent components. For this approach, individual functional data sets were decomposed into spatially independent components and corresponding time courses using ICA. A temporal filter (correlation with the expected brain response) was used to identify independent components time-locked to the tongue motor task. A spatial filter (cross-correlation with established neurofunctional systems) was used to identify brain activity not time-locked to the task. Our results confirm the importance of an extended bilateral cortical and subcortical network for the control of tongue movements, including the lateral primary sensorimotor cortex, supplementary motor cortex, anterior cingulate gyrus, insula, basal ganglia, thalamus, and cerebellum. Frontal tongue movements, highly overlearned movements related to speech production, showed less activity in parts of the frontal and parietal lobes compared to horizontal and vertical movements and greater activity in parts of the left frontal and temporal lobes compared to vertical movements. The investigation of inter-individual differences revealed a component representing the tongue primary sensorimotor cortex time-locked to the task in all participants. Using the spatial filter, we found the default mode network in 16 of 17 participants, the left fronto-parietal network in 16, the right fronto-parietal network in 8, and the executive control network in 4 participants. Further detailed analyses of speech-related tongue movements are warranted to increase our understanding of tongue motor control as a crucial part of articulation. Spatio-temporal filtering of independent components appears to be a powerful approach to study inter-individual differences in task-based functional MRI. This approach may be particularly useful for the assessment of individual patients and may be related to individual clinical, behavioral, and genetic information.

neuroscience↗