Evaluating the Effects of Model-Based Optimal Bipolar tDCS Configurations on Cortical Excitability

Sumientra Rampersad¹, Vincent Jansen², Edwin van Asseldonk³, Dick Stegeman4
¹Northeastern University, ²Radboud University Nijmegen Medical Centre, ³University of Twente, 4Radboud University Nijmegen Medical Centre

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique. Many positive effects of tDCS have been demonstrated in both healthy adults and neurological patients, but these effects are often small of short-lived. Volume conduction modeling results have suggested that the effects of tDCS may improve by using different electrode placements. Some novel configurations have been put forward, but experimental validation is scare. In a recent modeling study, we found optimal configurations for maximizing either the electric field strength or the electric field strength in the presumably most effective direction in a cortical target area. In the current study, these optimal configurations were compared with the conventional configuration for motor cortex stimulation for their effects on neuronal excitability. Three tDCS configurations were compared in a randomized crossover design with twenty healthy subjects. Corticospinal excitability was evaluated from electromyography of the right first dorsal interosseous muscle using single-pulse transcranial magnetic stimulation. Excitability was measured before and until 25 minutes after 15 minutes of 2 mA tDCS. The configuration that was optimized for field strength in the most effect direction produced significantly larger effects on group level than the configuration optimized for absolute field strength, and slightly larger effects than the conventional configuration. However, individual differences were large and should be taken into account.

Keywords: tDCS, Brain Stimulation, Modeling, FEM


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