Exp Brain Res (2006) 175:702–709 DOI 10.1007/s00221-006-0588-2 123 RESEARCH ARTICLE Modulation of steady-state auditory evoked potentials by cerebellar rTMS Maria A. Pastor · Gregor Thut · Alvaro Pascual-Leone Received: 7 March 2006 / Accepted: 2 June 2006 / Published online: 7 July 2006  Springer-Verlag 2006 Abstract Steady-state auditory evoked responses (SSAER) obtained via electroencephalography (EEG) co-vary in amplitude with blood Xow changes in the auditory area of the cerebellum. The aim of the present EEG study was to probe the cerebellar role in the con- trol of such SSAER. For this purpose, we investigated changes in SSAERs due to transient disruption of the cerebellar hemisphere by repetitive transcranial mag- netic stimulation (rTMS). SSAERs to click-trains of three diVerent frequencies in the gamma-band (32, 40 and 47 Hz) were recorded from 45 scalp electrodes in six healthy volunteers immediately after 1-Hz rTMS and compared to baseline SSAERs assessed prior to magnetic stimulation. Cerebellar rTMS contralateral to the stimulated ear signiWcantly reduced the amplitude of steady-state responses to 40-Hz click-trains and showed a tendency to reduce the amplitude to 32-Hz click-trains. No eVects were observed for 47-Hz click- trains, nor for magnetic stimulation of the cerebellum ipsilateral to auditory stimulation or after sham stimu- lation. Our results suggest that interference with cere- bellar output by rTMS modiWes functional activity associated with cortical auditory processing. The Wnd- ing of maximum eVects on 40-Hz SSAERs provides support to the notion that the cerebellum is part of a distributed network involved in the regulation of corti- cal oscillatory activity and points at some frequency- speciWcity for the control of auditory-driven neuronal oscillations. Keywords Steady state auditory evoked potentials · EEG · Repetitive TMS · Cerebellum Introduction Oscillatory responses of the brain, induced by rhythmic stimulation of a sensory pathway (steady-state poten- tials), follow the stimulation frequency and show a peak response at around 40 Hz for the auditory system, as revealed both via electroencephalography (EEG) and magnetoencephalography (MEG) using trains of auditory clicks or frequency-modulated tones (Regan 1966; Stapells et al. 1984; Ross et al. 2000; Simpson et al. 2005). Also, when a tone modulated in amplitude at increasing frequencies or chirp is presented, the maximal energies in EEG are found at stimulation fre- quencies around 40 Hz (Artieda et al. 2004). The source of this steady-state auditory evoked response (SSAER) has been localized in the primary auditory cortex, supratemporal gyrus, and brainstem via EEG, M. A. Pastor · G. Thut · A. Pascual-Leone Center for Noninvasive Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA M. A. Pastor (&) Center for Applied Medical Research and Department of the Neurological Sciences, University of Navarra, Medical School, Pamplona 31008, Spain e-mail: mapastor@unav.es Present Address: G. Thut Functional Brain Mapping Laboratory, Department of Neurology, University Hospital Geneva, Geneva, Switzerland A. Pascual-Leone Institut Guttman, Universitat Autónoma de Barcelona, Barcelona, Spain