• Hsiao-I Kuo, Marom Bikson, Abhishek Datta, Preet Minhas, Walter Paulus, Min-Fang Kuo, and Michael A Nitsche.
• Department of Clinical Neurophysiology, Georg-August-University Göttingen, Göttingen, Germany.
• Brain Stimul. 2013 Jul 1; 6 (4): 644-8.

BackgroundTranscranial direct current stimulation (tDCS) induces long-lasting NMDA receptor-dependent cortical plasticity via persistent subthreshold polarization of neuronal membranes. Conventional bipolar tDCS is applied with two large (35 cm(2)) rectangular electrodes, resulting in directional modulation of neuronal excitability. Recently a newly designed 4 × 1 high-definition (HD) tDCS protocol was proposed for more focal stimulation according to the results of computational modeling. HD tDCS utilizes small disc electrodes deployed in 4 × 1 ring configuration whereby the physiological effects of the induced electric field are thought to be grossly constrained to the cortical area circumscribed by the ring.ObjectiveWe aim to compare the physiological effects of both tDCS electrode arrangements on motor cortex excitability.MethodstDCS was applied with 2 mA for 10 min. Fourteen healthy subjects participated, and motor cortex excitability was monitored by transcranial magnetic stimulation (TMS) before and after tDCS.ResultsExcitability enhancement following anodal and a respective reduction after cathodal stimulation occurred in both, conventional and HD tDCS. However, the plastic changes showed a more delayed peak at 30 min and longer lasting after-effects for more than 2 h after HD tDCS for both polarities, as compared to conventional tDCS.ConclusionThe results show that this new electrode arrangement is efficient for the induction of neuroplasticity in the primary motor cortex. The pattern of aftereffects might be compatible with the concept of GABA-mediated surround inhibition, which should be explored in future studies directly.Copyright © 2013 Elsevier Inc. All rights reserved.

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