title: Effect of low-frequency repetitive transcranial magnetic stimulation on interhemispheric inhibition.
abstract: We studied the effects of 1-Hz repetitive transcranial magnetic stimulation (rTMS) on the excitability of interhemispheric connections in 13 right-handed healthy volunteers. TMS was performed using figure-eight coils, and surface electromyography (EMG) was recorded from both first dorsal interosseous (FDI) muscles. A paired-pulse method with a conditioning stimulus (CS) to the motor cortex (M1) followed by a test stimulus to the opposite M1 was used to study the interhemispheric inhibition (ppIHI). Both CS and TS were adjusted to produce motor-evoked potentials of approximately 1 mV in the contralateral FDI muscles. After baseline measurement of right-to-left IHI (pre-RIHI) and left-to-right IHI (pre-LIHI), rTMS was applied over left M1 at 1 Hz with 900 stimuli at 115% of resting motor threshold. After rTMS, ppIHI was studied using both the pre-rTMS CS (post-RIHI and post-LIHI) and an adjusted post-rTMS CS set to produce 1-mV motor evoked potentials (MEPs; post-RIHI(adj) and post-LIHI(adj)). The TS was set to produce 1-mV MEPs. There was a significant reduction in post-LIHI (P = 0.0049) and post-LIHI(adj) (P = 0.0169) compared with pre-LIHI at both interstimulus intervals of 10 and 40 ms. Post-RIHI was significantly reduced compared with pre-RIHI (P = 0.0015) but pre-RIHI and post-RIHI(adj) were not significantly different. We conclude that 1-Hz rTMS reduces IHI in both directions but is predominantly from the stimulated to the unstimulated hemisphere. Low-frequency rTMS may be used to modulate the excitability of IHI circuits. Treatment protocols using low-frequency rTMS to reduce cortical excitability in neurological and psychiatric conditions need to take into account their effects on IHI.
authors.affiliation: Divsion of Neurology and Krembil Neuroscience Centre, Toronto Western Research Institute, University Health Network, University of Toronto, Ontario, Canada.
authors.forename: Pramod Kr
authors.initials: PK
authors.lastname: Pal
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Hanajima
authors.forename: Carolyn A
authors.initials: CA
authors.lastname: Gunraj
authors.forename: Jie-Yuan
authors.initials: JY
authors.lastname: Li
authors.forename: Aparna
authors.initials: A
authors.lastname: Wagle-Shukla
authors.forename: Francesca
authors.initials: F
authors.lastname: Morgante
authors.forename: Robert
authors.initials: R
authors.lastname: Chen
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods*; D055590:Electromagnetic Phenomena; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology / Q000528:radiation effects; D005260:Female; D007839:Functional Laterality / Q000502:physiology / Q000528:radiation effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000528:radiation effects*; D009433:Neural Inhibition / Q000502:physiology / Q000528:radiation effects*; D013997:Time Factors