Electrical stimulation also uses electrical current to affect tissue healing. It is set up using either two or four electrode patches that are arranged on the skin like the four corners of a square. Once turned on, two electrical currents are passed through the electrodes, and the patient experiences a tingling or mild needle prick feeling. There may be a small muscular contraction under the electrode patches. This type of treatment is based upon the Gate Control Theory of pain perception. Depending upon the settings, the doctor can use electrical stimulation to decrease pain, increase circulation, decrease muscle spasm, re-educate the muscle fibers, reduce edema, and speed wound or fracture healing.