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Session: Neurophysiology: Clinical Neurophysiology
Session starts: Thursday 24 January, 13:30
Presentation starts: 14:45
Room: Lamoraalzaal

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Sumientra Rampersad ()
Thom Oostendorp ()
Dick Stegeman ()

Abstract:
Transcranial direct current stimulation (tDCS) entails sending a weak current through the head via two large planar electrodes attached to the scalp. This non-invasive stimulation painlessly induces polarity dependent cortical excitability modulations, making tDCS a promising technique for neurostimulation. Transcranial DC stimulation has been shown propitious in improving brain function in patients with neurological diseases like chronic pain, stroke, Parkinson’s disease, depression and epilepsy. Unfortunately, the effects are still too small and short-lived for tDCS to be used as a clinical therapy. Increasing the effect size of tDCS could possibly be achieved by better targeting the current, both in direction and amplitude. Volume conduction modeling studies have shown that the areas with the highest electric fields strengths do not, as is often assumed, lie beneath the electrodes. In order to find an electrode configuration that does result in maximum and more focal stimulation at the target area, we propose an inverse modeling approach. We simulate tDCS for ~7000 configurations and afterward determine which configuration leads to a maximal electric field at several target locations that are commonly used in tDCS research. A highly detailed finite element model of the complete head of a 25-year-old male was created by automatic segmentation of MR images followed by manual corrections. The model contains over 4 million tetrahedral elements and eleven tissue types. Special attention was given to the skull, the main barrier for the stimulation current, by including the spongiosa layer and skull holes. Anisotropy was derived from DTI measurements. To our knowledge, this is currently the most detailed model used for simulating tDCS. From the surface of this model, 86 equally spaced nodes were selected. For each combination of two points from this set, we placed 5 x 5 cm electrode patches onto the head model, centred on the two points, and simulated 1 mA tDCS. By comparing the direction and amplitude of the resulting electric field in the target area in all configurations, we determined the optimal stimulation configurations for motor cortex, dorsolateral prefrontal cortex, inferior frontal gyrus, occipital cortex and cerebellum stimulation. This approach can be used to optimize stimulation for any target location. We found different optimal configurations by looking at either strength or direction of the field. Comparing these configurations experimentally will not only verify our modeling approach, but also provide valuable information on the mechanisms behind tDCS.