- Paired-pulse transcranial magnetic stimulation: This test measures changes in brain activity. A wire coil is held on the scalp and a brief electrical current is passed through the coil, creating a magnetic pulse that stimulates the brain. The subject hears a click and may fee a pulling sensation on the skin under the coil, and there may be a twitch in the muscles of the face, arm or leg. Subjects may be asked to tense certain muscles slightly or perform other simple actions.