Biology subjects

Radecke, J.-O.

Publications and source records attributed to Radecke, J.-O..

5 recordsLinked to original sources

bioRxiv2024

Personalized tDCS targeting visual motion area V5 modulates smooth pursuit initiation

Transcranial direct current stimulation (tDCS) for the modulation of ongoing eye movements provides an ideal model for investigating sensorimotor integration. Within neural networks subserving smooth pursuit eye movements, visual motion area V5 is a core hub to integrate visual motion information with oculomotor control. Here, we applied personalized tDCS explicitly targeting individual V5 in healthy human participants using algorithmic optimization informed by functional magnetic resonance imaging and combined electro- and magnetencephalography. We hypothesized subtle modulation of sensorimotor integration during pursuit and assessed the gain by personalized tDCS targeting V5, compared to personalized tDCS targeting the frontal eye field, as well as conventional normative tDCS over V5. Indeed, pursuit initiation was specifically delayed during personalized cathodal tDCS targeting right V5 indicating the involvement of distinct functional subregions of V5 in the initial sensorimotor integration of visual motion information with pursuit eye movements, but not the maintenance of ongoing pursuit. The results were well-controlled by anodal and sham tDCS, different pursuit tasks, finite-element simulations of individual electric fields, and by two additional control experiments, one that applied personalized tDCS targeting frontal eye field and another that applied normative tDCS over V5. Importantly, in contrast to personalized tDCS targeting FEF and normative tDCS over V5, personalized tDCS targeting V5 effectively modulated pursuit by adapting electric fields to individual anatomical and functional V5 properties. Our results provide evidence for the specific involvement of area V5 in sensorimotor integration during pursuit initiation and the ability of (targeted) tDCS to specifically introduce subtle modulation of the brain network underlying smooth pursuit eye movements. Further, our results indicate the potential of personalized tDCS to alter behavior as the main aspect of interest in human neuromodulation.

neuroscience↗

bioRxiv2023

Transcranial electrical stimulation over premotor cortex mimics attentional modulation of visual processing

Attentional control over sensory processing has been linked to neural alpha oscillations and related pulsed inhibition of the human cortex. Despite the wide consensus on the functional relevance of alpha oscillations for attention, precise neural mechanisms of how alpha oscillations shape perception and how this top-down modulation is implemented in cortical networks remain unclear. Here, we tested the hypothesis that alpha oscillations in premotor cortex are causally involved in top-down regulation of visual cortex responsivity to contrast. We applied intermittent transcranial alternating current stimulation (tACS) over bilateral premotor cortex to manipulate attentional preparation in a visual discrimination task. tACS was applied at 10 Hz (alpha) and controlled with 40 Hz (gamma) and sham stimulation. Importantly, we used a novel linear mixed modeling approach for statistical control of neurosensory side-effects of the electric stimulation. We found a frequency-specific effect of alpha tACS on the slope parameter, leading to enhanced low-contrast perception and decreased perception of high-contrast stimuli. Side-effects affected both threshold and slope parameters, leading to high variability in parameter estimates. Controlling the impact of side-effects on psychometric parameters by linear mixed model analysis reduced variability and clarified the existing effect. We conclude that alpha tACS over premotor cortex mimicked a state of increased endogenous attention potentially by modulation of fronto-occipital connectivity in the alpha band. We speculate that this network modulation allowed for improved sensory readout from visual cortex which led to a decrease in psychometric slope, effectively broadening the dynamic range for contrast perception. Significance statementAttention is fundamental to voluntary control of perception and behavior. Yet, despite extensive scientific efforts, precise underlying neural mechanisms remain elusive. We contribute to this ongoing discussion by providing evidence for a vital role of frontal alpha oscillations in regulating the responsivity of visual cortex. By controlled neuromodulation with intermittent transcranial alternating current stimulation (tACS), we show that alpha tACS modulates psychometric properties of visual contrast perception. This study fills an important gap between work on alpha oscillations in spatial attention and studies on the psychometrics of attention. Furthermore, we pioneered an approach for the statistical control of tACS side-effects with linear mixed modeling and thereby add to the ongoing debate on outcome variability in studies using transcranial neurostimulation methods.

neuroscience↗

bioRxiv2023

Personalized alpha-tACS targeting left posterior parietal cortex modulates visuo-spatial attention and posterior evoked EEG activity

BackgroundCovert visuo-spatial attention is marked by the anticipatory lateralization of neuronal alpha activity in the posterior parietal cortex. Previous applications of transcranial alternating current stimulation (tACS) at the alpha frequency, however, were inconclusive regarding the causal contribution of oscillatory activity during visuo-spatial attention. ObjectiveAttentional shifts of behavior and electroencephalography (EEG) after-effects were assessed in a cued visuo-spatial attention paradigm. We hypothesized that parietal alpha-tACS facilitates attention in the ipsilateral visual hemifield. Furthermore, we assumed that modulations of behavior and neurophysiology are related to individual electric field simulations. MethodsWe applied personalized tACS at alpha and gamma frequencies to elucidate the role of oscillatory neuronal activity for visuo-spatial attention. Personalized tACS montages were algorithmically optimized to target individual left and right parietal regions that were defined by an EEG localizer. ResultsBehavioral performance in the left hemifield was specifically increased by alpha-tACS compared to gamma-tACS targeting the left parietal cortex. This hemisphere-specific effect was observed despite the symmetry of simulated electric fields. In addition, visual event-related potential (ERP) amplitudes showed a reduced lateralization over posterior sites induced by left alpha-tACS. Neuronal sources of this effect were localized in the left premotor cortex. Interestingly, accuracy modulations induced by left parietal alpha-tACS were directly related to electric field magnitudes in the left premotor cortex. ConclusionOverall, results corroborate the notion that alpha lateralization plays a causal role in covert visuo-spatial attention and indicate an increased susceptibility of parietal and premotor brain regions of the left dorsal attention network to subtle tACS-neuromodulation.

neuroscience↗

bioRxiv2021

Electrical neuromodulation biases brightness perception of flickering light

BackgroundVisual phenomena like brightness illusions impressively demonstrate the highly constructive nature of perception. In addition to physical illumination, the subjective experience of brightness is related to temporal neural dynamics in visual cortex. ObjectiveHere, we asked whether biasing the temporal pattern of neural excitability in visual cortex by transcranial alternating current stimulation (tACS) modulates brightness perception of concurrent rhythmic visual stimuli. MethodsParticipants performed a brightness discrimination task of two flickering lights, one of which was targeted by same-frequency electrical stimulation at varying phase shifts. tACS was applied with an occipital and a periorbital active control montage, based on simulations of electrical currents using finite-element head models. ResultsExperimental results reveal that flicker brightness perception is modulated dependent on the phase shift between sensory and electrical stimulation, solely under occipital tACS. Phase-specific modulatory effects by tACS were dependent on flicker-evoked neural phase stability at the tACS-targeted frequency, recorded prior to electrical stimulation. The optimal timing of tACS application leading to enhanced brightness perception was further correlated with the neural phase delay of the cortical flicker response. ConclusionsOur results corroborate the role of temporally coordinated neural activity in visual cortex for brightness perception of rhythmic visual input in humans. Phase-specific behavioral modulations by tACS emphasize its efficacy to transfer perceptually relevant temporal information to the cortex. These findings provide an important step towards understanding the basis of visual perception and further confirm electrical stimulation as a tool for advancing controlled modulations of neural activity and related behavior.

neuroscience↗

bioRxiv2019

Simulating individually targeted transcranial electric stimulation for experimental application

Transcranial electric stimulation (tES) induces electric fields that are subject to a complex interaction with individual anatomical properties, such as the low-conducting human skull, the distribution of cerebrospinal fluid or the sulcal depth, as well as stimulation target location and orientation. This complex interaction might contribute to the heterogenous results that are commonly observed in applications of tES in humans. Targeted tES, on the other hand, might be able to account for some of these individual factors. In the present study, we used the finite-element method (FEM) and head models of twenty-one participants to evaluate the effect of individually targeted tES on simulated intracranial current densities. Head models were based on an automated segmentation algorithm to facilitate processing in experimental sample sizes. We compared a standard stimulation montage to two individually optimized tES montages using an Alternating Direction Method of Multipliers (ADMM) and a Constrained Maximum Intensity (CMI) approach. A right parietal target was defined with three different orientations. Individual current densities showed varying intensity and spatial extent near the lower limit at which physiological efficacy of electric fields can be assumed. Both individually optimized targeting algorithms were able to control the electric field properties, with respect to intensities and/or spatial extent of the electric fields. Still, across head models, intensity in the stimulation target was constrained by individual anatomical properties. Thus, our results underline the importance of targeted tES in enhancing the effectiveness of future tES applications and in elucidating the underlying mechanisms.

neuroscience↗