Subdural recordings from an awake human brain for measuring current intensity during transcranial direct current stimulation.

Transcranial direct current stimulation (tDCS) is an emerging method, used for non-invasively stimulating the brain in normal healthy subjects and in patients with neurological disorders. However, the pattern of the spatial distribution of the current intensity induced by tDCS is poorly understood. In this study, we directly measured the spatial characteristics of the current intensity induced by tDCS using an intracranial strip electrode array implanted over the motor cortex in patients with Parkinson's disease undergoing deep brain stimulation lead placement surgery. We used a bilateral stimulation configuration for the tDCS electrode placement and measured the amount of electric current passing through the contacts along the implanted strip electrode contacts. Our results showed significant changes of the current flow induced by the tDCS in some of the contacts during stimulation with respect to baseline activities. These results may provide vital information regarding the biophysical effects of tDCS stimulation and might be potentially useful for developing more effective stimulation strategies.