Interindividual variability of the modulatory effects of repetitive transcranial magnetic stimulation on cortical excitability

• Published in: Experimental brain research Vol. 133; no. 4; pp. 425 - 430
• Main Authors: MAEDA, F, KEENAN, J. P, TORMOS, J. M, TOPKA, H, PASCUAL-LEONE, A
• Format: Journal Article
• Language: English
• Published: Berlin Springer 04.08.2000
• Subjects: Biological and medical sciences; Cerebral Cortex - physiology; Electric Stimulation - methods; Electromagnetic Phenomena; Evoked Potentials, Motor - physiology; Fundamental and applied biological sciences. Psychology; Humans; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Vertebrates: nervous system and sense organs; Human; Stimulus frequency; Motor pathway; Motor cortex; Modulation; Central nervous system; Magnetic stimulus; Repetitive stimulus; Electrophysiology; Excitability; Motor evoked potential; Brain (vertebrata)
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s002210000432

Repetitive transcranial magnetic stimulation (rTMS) appears to have effects on cortical excitability that extend beyond the train of rTMS itself. These effects may be inhibitory or facilitatory and appear to depend on the frequency, intensity, duration and intertrain interval of the rTMS. Many studies assume facilitatory effects of high-frequency rTMS and inhibitory effects of low-frequency rTMS. Nevertheless, the interindividual variability of this modulation of cortical excitability by rTMS has not been systematically investigated. In this study, we applied 240 pulses of rTMS at 90% of the subjects' motor threshold to their motor cortex at different frequencies (1, 10, 15 and 20 Hz) and examined the effects on motor evoked potentials (frequency tuning curve). Although the averaged group data showed a frequency-dependent increase in cortical excitability, each subject had a different pattern of frequency tuning curve, i.e. a different modulatory effect on cortical excitability at different rTMS frequencies. The interindividual variability of these modulatory effects was still high, though less so, when the number of rTMS pulses was increased to 1,600. These findings illustrate the degree of variability of the rTMS effects in the human brain.