Cerebral Cortex Advance Access originally published online on February 20, 2009
Cerebral Cortex 2009 19(11):2605-2615; doi:10.1093/cercor/bhp013
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Stimulus–Response Profile during Single-Pulse Transcranial Magnetic Stimulation to the Primary Motor Cortex
1 Department of Cortical Function Disorders, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Kodaira 187-8502, Japan, 2 PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan, 3 Human Brain Research Center, Kyoto University Graduate School of Medicine, Kyoto 606-8507, Japan, 4 Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto 606-8507, Japan, 5 Musashino Hospital, Ageo 362-0033, Japan, 6 CREST, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan
Address correspondence to Takashi Hanakawa, MD, PhD, Department of Cortical Function Disorders, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187-8502, Japan. Email: hanakawa{at}ncnp.go.jp.
We examined the stimulus–response profile during single-pulse transcranial magnetic stimulation (TMS) by measuring motor-evoked potentials (MEPs) with electromyographic monitoring and hemodynamic responses with functional magnetic resonance imaging (fMRI) at 3 Tesla. In 16 healthy subjects, single TMS pulses were irregularly delivered to the left primary motor cortex at a mean frequency of 0.15 Hz with a wide range of stimulus intensities. The measurement of MEP proved a typical relationship between stimulus intensity and MEP amplitude in the concurrent TMS-fMRI environment. In the population-level analysis of the suprathreshold stimulation conditions, significant increases in hemodynamic responses were detected in the motor/somatosensory network, reflecting both direct and remote effects of TMS, and also the auditory/cognitive areas, perhaps related to detection of clicks. The stimulus–response profile showed both linear and nonlinear components in the direct and remote motor/somatosensory network. A detailed analysis suggested that the nonlinear components of the motor/somatosensory network activity might be induced by nonlinear recruitment of neurons in addition to sensory afferents resulting from movement. These findings expand our basic knowledge of the quantitative relationship between TMS-induced neural activations and hemodynamic signals measured by neuroimaging techniques.
Key Words: functional connectivity • functional MRI • motor-evoked potentials • multidisciplinary brain mapping • transcranial magnetic stimulation