Abstract
Objective. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique to modify neural excitability. Using multi-array tDCS, we investigate the influence of inter-individually varying head tissue conductivity profiles on optimal electrode configurations for an auditory cortex stimulation. Approach. In order to quantify the uncertainty of the optimal electrode configurations, multi-variate generalized polynomial chaos expansions of the model solutions are used based on uncertain conductivity profiles of the compartments skin, skull, gray matter, and white matter. Stochastic measures, probability density functions, and sensitivity of the quantities of interest are investigated for each electrode and the current density at the target with the resulting stimulation protocols visualized on the head surface. Main results. We demonstrate that the optimized stimulation protocols are only comprised of a few active electrodes, with tolerable deviations in the stimulation amplitude of the anode. However, large deviations in the order of the uncertainty in the conductivity profiles could be noted in the stimulation protocol of the compensating cathodes. Regarding these main stimulation electrodes, the stimulation protocol was most sensitive to uncertainty in skull conductivity. Finally, the probability that the current density amplitude in the auditory cortex target region is supra-threshold was below 50%. Significance. The results suggest that an uncertain conductivity profile in computational models of tDCS can have a substantial influence on the prediction of optimal stimulation protocols for stimulation of the auditory cortex. The investigations carried out in this study present a possibility to predict the probability of providing a therapeutic effect with an optimized electrode system for future auditory clinical and experimental procedures of tDCS applications.
Highlights
Transcranial direct current stimulation is a non-invasive method, which modulates cortical excitability in the human brain [1]
The results suggest that an uncertain conductivity profile in computational models of Transcranial direct current stimulation (tDCS) can have a substantial influence on the prediction of optimal stimulation protocols for stimulation of the auditory cortex
Regarding the effect on the current density, the largest effects were on the zcomponent for gray matter and white matter conductivity, while those for skin and skull conductivity were similar in all components
Summary
Transcranial direct current stimulation (tDCS) is a non-invasive method, which modulates cortical excitability in the human brain [1]. Computer simulation studies of the induced current flow pattern in detailed MRI-derived finite element (FE) head models demonstrated that the cortical current flow pattern is rather broad with often maximal stimulation in non-target brain regions [2, 3]. Taking into account Helmholtz reciprocity, the reported results were in agreement with a simulation study comparing PEM and CEM for source analysis and reconstruction in electroencephalography (EEG) modeling [10]. Both studies suggest that the application of PEM in the current study allows for a sufficiently accurate modeling of the current density within brain regions compared to CEM. While a guideline for efficient yet accurate volume conductor modeling in tDCS has been presented [2], the influence of interindividually varying conductivity profiles is rather unclear
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