title: Intracranial measurement of current densities induced by transcranial magnetic stimulation in the human brain.
abstract: Transcranial magnetic stimulation (TMS) is a non-invasive technique that uses the principle of electromagnetic induction to generate currents in the brain via pulsed magnetic fields. The magnitude of such induced currents is unknown. In this study we measured the TMS induced current densities in a patient with implanted depth electrodes for epilepsy monitoring. A maximum current density of 12 microA/cm2 was recorded at a depth of 1 cm from scalp surface with the optimum stimulation orientation used in the experiment and an intensity of 7% of the maximal stimulator output. During TMS we recorded relative current variations under different stimulating coil orientations and at different points in the subject's brain. The results were in accordance with current theoretical models. The induced currents decayed with distance form the coil and varied with alterations in coil orientations. These results provide novel insight into the physical and neurophysiological processes of TMS.
authors.affiliation: Laboratory for Magnetic Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave KS-454, Boston, MA 02215, USA.
authors.forename: Tim
authors.initials: T
authors.lastname: Wagner
authors.forename: Massimo
authors.initials: M
authors.lastname: Gangitano
authors.forename: Rafael
authors.initials: R
authors.lastname: Romero
authors.forename: Hugo
authors.initials: H
authors.lastname: Théoret
authors.forename: Masahito
authors.initials: M
authors.lastname: Kobayashi
authors.forename: David
authors.initials: D
authors.lastname: Anschel
authors.forename: John
authors.initials: J
authors.lastname: Ives
authors.forename: Neil
authors.initials: N
authors.lastname: Cuffin
authors.forename: Donald
authors.initials: D
authors.lastname: Schomer
authors.forename: Alvaro
authors.initials: A
authors.lastname: Pascual-Leone
mesh_terms: D000328:Adult; D016477:Artifacts; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D001930:Brain Injuries / Q000150:complications / Q000503:physiopathology; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods*; D004567:Electrodes, Implanted; D004574:Electromagnetic Fields; D017029:Epilepsy, Complex Partial / Q000209:etiology / Q000503:physiopathology; D005260:Female; D006801:Humans; D008959:Models, Neurological; D012886:Skull / Q000033:anatomy & histology / Q000502:physiology; D050781:Transcranial Magnetic Stimulation