Direct Measurement of Motor Cortical Responses to tDCS

Subjects will enter the EEG lab and be seated in a chair. The 26-electrode EEG array will be placed using a conductive paste. The electrodes will be connected to a clinical grade EEG machine used in standard of care routine EEG monitoring. Next, a soft cloth cap will be placed over the subject's head with the tDCS electrodes pre-positioned in place. The cap will be positioned so that the tDCS electrodes cover the scalp without disturbing the underlying EEG electrodes. Conducting gel will be applied in direct contact with the scalp to facilitate stimulation. In addition, lidocaine jelly will be added topically to provide local anesthesia. The tDCS electrodes will be connected to a low-current generator. Participants receive 2.0 milliamps in electrical stimulation from the tDCS machine for 20 minutes. The device will be manually controlled by study personnel assisting with the experiment. A virtual reality environment will be utilized to collect kinematic data during the study.

Subjects receiving sham undergo the same setup as the stimulation group with the exception that sham subjects experience stimulation for one minute only (30 second ramp-up to 2 milliamps immediately followed by 30 second ramp-down to 0 milliamps for the remaining 19 minutes). This provides similar sensory feedback to sham subjects that treatment subjects experience. The same electrode array, soft cloth cap, conducting gel application, and lidocaine are applied as in a stimulation subject. The tDCS electrodes will be connected to a low-current generator. A virtual reality environment will be utilized to collect kinematic data during the study.

Subjects are brought into the operating room. The scalp is prepped with a sterilizing solution. Following infiltration with local anesthetic and incision, a 6-contact electrocorticography strip is inserted into the burr hole covering primary motor cortex. Electrocorticography strip terminals are connected to an amplifier for signal recording. Gas-sterilized transcranial direct current stimulation electrodes are placed on the scalp directly overlying primary motor cortex. tDCS electrodes are connected to a low-current generator. During electrocorticographic recording, stimulation is turned on while subjects are asked to flex each arm. At the conclusion of the experiment, the electrocorticography strip and tDCS electrodes are removed and the surgery proceeds as planned.