Meta-analytic electric field modeling and developing multi-scale models

Abstract

Abstract In this talk, I will present two recent developments of my lab using electric field modeling. First, I will talk about our efforts in combining electric field modeling with traditional meta-analysis on the effects of tDCS on working memory. Due to differences in electrode montages and stimulation intensities across different studies, results are difficult to aggregate for meta-analytic inferences. To overcome these limitations, we have developed a novel meta-analytic method relating behavioral effect sizes to electric field strength, to identify brain regions underlying the largest tDCS-induced WM improvement. Simulations on 69 studies targeting left prefrontal cortex showed that tDCS electric field strength in lower dorsolateral prefrontal cortex (Brodmann area 45/47) relates most strongly to improved WM performance. This brain region could be a target area for future tDCS studies. Our metanalytic framework can be applied to other stimulation modalities and behavioral measures. In the second part, I will talk about our efforts developing multi-scale models for TMS. While the induced electric field is the key factor to determine dosing and target engagement, it is only a first step to model the physiological response. To advance these efforts we have developed a new multi-scale pipeline (NeMo-TMS) for modeling TMS effects across spatial scales. On the macro-scale, we simulate TMS electric fields using SimNIBS. Afterwards, simulated electric fields from the previous step are coupled with morphologically realistic neuronal models in the NEURON environment. These neuron-scale simulations allow the investigation of membrane voltage (depolarization/hyperpolarization), action potential initiation and propagation, field intensity, and orientation necessary for modulating neuron response, etc. Finally, we incorporate the membrane voltage data to simulate the calcium concentration induced by voltage-gated calcium-channels at the subcellular scale by solving the calcium dynamics equations. This allows us to model effects of rTMS protocols on somatic calcium accumulation, important for neural plasticity.