166 Boutros et al. © 2000 WILEY-LISS, INC. DEPRESSION AND ANXIETY 12:166–169 (2000) ELECTROENCEPHALOGRAM AND REPETITIVE TRANSCRANIAL MAGNETIC STIMULATION Nashaat N. Boutros, M.D., 1,2 * Robert M. Berman, M.D., 1,3 Ralph Hoffman, M.D., 1,4 Alexander P. Miano, M.D., 1,3 Duane Campbell, B.A., 1,2 and Risto Ilmoniemi, Ph.D. 5 Scalp recordings of the electroencephalogram (EEG) have been used in associa- tion with repetitive transcranial magnetic stimulation (rTMS) investigations as a safety measure in monitoring ongoing EEG activity and as a neurophysiologic tool in examining the specific effects induced by the magnetic stimulus on the EEG or evoked potentials (EPs). Medline review on the use of EEG or EPs with rTMS reveals that this area has been largely unexplored. Limited available stud- ies attest to the potential for studies combining EEG/EPs and rTMS to be useful in further elucidating the normal brain physiology. Herein, we report on our experience with continuous EEG sampling combined with rTMS in patients with major depression (n = 14), schizophrenia (n = 7), and obsessive–compulsive disor- der (n = 5). Our data support the practice of using continuous EEG monitoring when the stimulation parameters fall outside established safety guidelines. De- pression and Anxiety, 12:166–169, 2000. © 2000 Wiley-Liss, Inc. Key words: electroencephalogram; EEG; evoked potentials; repetitive transcranial magnetic stimulation; rTMS; depression; schizophrenia; obsessive–compulsive disorder INTRODUCTION In the last few years, repetitive transcranial magnetic stimulation (rTMS) has emerged as both a potential therapeutic modality and an investigative tool. RTMs seems to hold a significant promise for contributing to the understanding of the basic brain neurophysiology as well as the pathophysiology of neuropsychiatric dis- orders. To date, scalp recordings of the electroen- cephalogram (EEG) have been used in association with rTMS investigations in two ways: as a safety measure in monitoring ongoing EEG activity and as a neuro- physiologic tool in examining the specific effects in- duced by the magnetic stimulus on the EEG or evoked potentials (EPs). Herein, we will first review currently available literature on the coupling of EEG or EPs technology with rTMS. Additionally, we will present data from our experience with continuous EEG sam- pling in patients with major depression, schizophrenia, and obsessive–compulsive disorder (OCD). EEG AND EPS AS TOOLS FOR EXAMINING THE EFFECTS OF RTMS Examination of the effects of rTMS on the EEG and EPs remains in its infancy. Before this field can rapidly 1 Department of Psychiatry, Yale University School of Medi- cine, New Haven, Connecticut 2 VA Connecticut Healthcare System, West Haven Campus, West Haven, Connecticut 3 Connecticut Mental Health Center, New Haven, Connecticut 4 Yale Psychiatric Institute, New Haven, Connecticut 5 Biomag Laboratory, Medical Engineering Centre, Helsinki University Central Hospital, Helsinki, Finland Contract grant sponsor: Veterans Administration; Contract grant sponsor: NARSAD; Contract grant sponsor: TEKES Foundation and Helsinki University Central Hospital. *Correspondence to: Dr. Nashaat N. Boutros, Department of Psy- chiatry, Yale University School of Medicine and VA-Connecticut Healthcare System, 950 Campbell Avenue, West Haven CT 06516. E-mail: nash.boutros@yale.edu Received for publication 21 August 2000; Accepted 21 August 2000 expand, some of the technical difficulties associated with the influence of magnetic stimulators on EEG recording systems need to be resolved. Information processing and stimulus conduction in the central nervous system (CNS) are extremely fast processes. Most of the neuronal com- munication within the CNS occurs in milliseconds. If standard EEG amplifiers are used during magnetic