After-effects of anodal transcranial direct current stimulation on the excitability of the motor cortex in rats

Purpose: Transcranial direct current stimulation (tDCS) is increasingly seen as a useful tool for noninvasive cortical neuromodulation. A number of studies in humans have shown that when tDCS is applied to the motor cortex it can modulate cortical excitability. It is especially interesting to note that when applied with sufficient duration and intensity, tDCS can enable long-lasting neuroplastic effects. However, the mechanism by which tDCS exerts its effects on the cortex is not fully understood. We investigated the effects of anodal tDCS under urethane anesthesia on field potentials in in vivo rats. Methods: These were measured on the skull over the right motor cortex of rats immediately after stimulating the left corpus callosum. Results: Evoked field potentials in the motor cortex were gradually increased for more than one hour after anodal tDCS. To induce these long-lasting effects, a sufficient duration of stimulation (20 minutes or more) was found to may be required rather than high stimulation intensity. Conclusion: We propose that anodal tDCS with a sufficient duration of stimulation may modulate transcallosal plasticity.