All subjects complete a questionnaire regarding their mood and alertness and then perform tests of thumb or wrist movement. For this test, a small electrical stimulus is applied to the side of the hand and the subject must respond to the stimulus as quickly as possible by making a thumb or wrist movement. This is repeated several times over about 3 minutes. A second test follows in which the subject moves the thumb or wrist in response to a beep from a speaker. This test is repeated several times over about 8 minutes. Some measurements are taken using single-pulse TMS during the beginning, middle and end of this test. In two of the four sessions, theta burst stimulation is applied after the single-pulse TMS and in the other two sessions, sham theta burst stimulation is applied.