Functional magnetic resonance imaging and transcranial magnetic stimulation: Effects of motor imagery, movement and coil orientation D.M. Niyazov a, * , A.J. Butler b , Y.M. Kadah a , C.M. Epstein c , X.P. Hu a a Department of Biomedical Engineering, Emory University School of Medicine, Hospital Annex, 531 Asbury Circle, Suite N305, Atlanta, GA 30322, USA b Department of Rehabilitation Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA c Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322, USA Accepted 21 February 2005 Available online 27 April 2005 Abstract Objective: To compare fMRI activations during movement and motor imagery to corresponding motor evoked potential (MEP) maps obtained with the TMS coil in three different orientations. Methods: fMRI activations during executed (EM) and imagined (IM) movements of the index finger were compared to MEP maps of the first dorsal interosseus (FDI) muscle obtained with the TMS coil in anterior, posterior and lateral handle positions. To ensure spatial registration of fMRI and MEP maps, a special grid was used in both experiments. Results: No statistically significant difference was found between the TMS centers of gravity (TMS CoG) obtained with the three coil orientations. There was a significant difference between fMRI centers of gravity during IMs (IM CoG) and EMs (EM CoG), with IM CoGs localized on average 10.3 mm anterior to those of EMs in the precentral gyrus. Most importantly, the IM CoGs closely matched cortical projections of the TMS CoGs while the EM CoGs were on average 9.5 mm posterior to the projected TMS CoGs. Conclusions: TMS motor maps are more congruent with fMRI activations during motor imagery than those during EMs. These findings are not significantly affected by changing orientation of the TMS coil. Significance: Our results suggest that the discrepancy between fMRI and TMS motor maps may be largely due to involvement of the somatosensory component in the EM task. q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: fMRI; BOLD; TMS; CoG; Motor cortex; Motor imagery 1. Introduction Transcranial magnetic stimulation (TMS) is a method that allows for noninvasive stimulation of neurons in localized regions of cortex (Lazzaro et al., 2004). It is widely used as a research tool in neurosciences and therapeutic management of patients with a variety of neuro-psychiatric disorders (Schlaepfer et al., 2003; Tassinari et al., 1990). However, with almost two decades of TMS use since it was introduced by Barker et al. (1985), the exact stimulation site on the cortex remains under debate despite multiple attempts to define it (Epstein et al., 1990; Terao et al., 1998; Thielscher and Kammer, 2002). This stimulation site, or TMS maximum, is the point of maximum electric field, running along the line perpendicular to the center of the figure-of-eight coil (Kobayashi and Pascual-Leone, 2003). Knowledge of TMS maximum is crucial to accurate positioning of the coil in studying normal and pathological cerebral functions. Functional magnetic resonance imaging (fMRI) has been used to study the cortical effects of TMS noninvasively because of its high spatial and temporal resolution (Brett et al., 2002). fMRI measures the hemodynamic correlates of neural activity (Ogawa et al., 1992) and allows for mapping functional activity and connectivity in humans (Matthews and Jezzard, 2004). In fMRI experiments, fast sequences Clinical Neurophysiology 116 (2005) 1601–1610 www.elsevier.com/locate/clinph 1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2005.02.028 * Corresponding author. Tel.: C1 404 712 2618; fax: C1 404 712 2707. E-mail address: dniyazov@bme.emory.edu (D.M. Niyazov).