- Experiment 2: Participants will have DC brain polarization performed with transcranial magnetic stimulation (TMS), which uses magnetic pulses to activate nerve cells in the brain. We will use TMS to help us understand how far the effect of DC polarization spreads in the brain. After attaching electrodes to a point on the scalp above the ear, researchers will give about 50 TMS pulses to five different places near this area. These pulses will produce some painless muscle twitches in the hand or arm. The TMS pulses will be followed by the DC brain polarization, and then by another set of TMS pulses to see if there are any differences in muscle response.