Effects of neuroplasticity by repetitive anodal transcranial direct current stimulation on the human motor cortex

Aim of the study was to investigate the effects of repeated anodal tDCS on the human motor-cortex. tDCS is a non-invasive brain stimulation techniques, which is able to produce neuroplasticity changes in humans. So far anodal tDCS was able to produce cortical excitability-ehancement stable for one hour after the end of the stimulation in humans. We tried to induce prolonged excitability changes via spaced anodal transcranial direct current stimulation. Spaced stimulation protocols in animals or slice preparations could produce long-lasting neuroplastic alterations, stable for several hours or even days, called late-phase long-term potentiation (l-LTP). These changes in synaptic strength seem to be important for the formation of learning and memory processes. In 15 healthy subjects 13 minutes repetitive anodal tDCS of 1mA with an interstimulation interval of 0 min, 3 min, 20 min, 3 hours or 24 hours was performed. Repeated anodal tDCS with short breaks (3 min, 20 min) led – after an initial slight reduction – to an enhancement of cortical excitability which was present more than 24 hours after tDCS. The stimulation protocols making use of long breaks (3 hours, 24 hours) resulted in the formation of homeostatic plasticity changes. Doubling the stimulation duration (26 min) induced a reduction of cortical excitability, which could be abolished in a second experiment via use of calcium channel antagonist flunarizin. In conclusion, repetitive anodal tDCS with an interstimulation interval of several minutes is able to induce l-LTP-like plasticity in the human motor cortex. The results might help to improve learning protocols in humans and the efficacy of tDCS in clinical studies to optimize the treatment of patients with neuropsychiatric disease.2013-02-0