Neuropediatrics 2010; 41 - V1258
DOI: 10.1055/s-0030-1265520

Low-Frequency rTMS selectively modulates inhibitory intracortical networks

I Delvendahl 1, N Jung 1, F Mainberger 1, V Mall 1
  • 1Universitätsklinikum Freiburg

Introduction: Repetitive transcranial magnetic stimulation (rTMS) can induce bidirectional plasticity in human motor cortex depending on frequency. At a very low frequency of 0.1Hz, however, no plasticity is induced (Chen et al., 1997). There is on the other hand evidence that 0.1Hz rTMS con, for instance, influence following induction of plasticity. We therefore investigated if 0.1Hz rTMS modulates intracortical inhibitory phenomena.

Methods: We performed rTMS on 10 healthy volunteers (mean age 25±2 years, 6 female, 4 male). RTMS consisted of 250 stimuli at a frequency of 0.1Hz. Before and after this intervention we measured amplitudes of motor evoked potentials (MEP), resting motor threshold (MT), intracortical facilitation (ICF), cortical silent period (CSP) duration as well as short-interval (SICI) and long-interval intracortical inhibition (LICI).

Results: MEP amplitudes, MT, ICF and CSP duration remained unchanged after rTMS. SICI and LICI, however, were significantly enhanced after 250 stimuli of 0.1Hz rTMS (SICI at 3ms inter-stimulus interval (ISI): 55.5% to 68.2%, p=0.037, LICI at 100ms ISI: 61.9% to 88.8%, p=0.014).

Discussion: As previously described, we observed no significant change of MEP amplitudes or MT and thus no induction of plasticity by 0.1Hz rTMS. Intracortical inhibition, however, was significantly enhanced after rTMS. SICI at 3ms ISI and LICI represent GABAergic inhibition in human motor cortex and are selectively modulated by 0.1Hz rTMS. These changes in intracortical inhibitory circuits fit into the concept of gating (Ziemann & Siebner, 2008) and could thus influence plasticity inducing protocols.

Literature: [1] Chen, R., Classen, J., Gerloff, C., Celnik, P., Wassermann, E.M., Hallett, M. & Cohen, L.G. (1997) Depression of motor cortex excitability by low-frequency transcranial magnetic stimulation. Neurology, 48, 1398–1403. [2] Ziemann, U. & Siebner, H.R. (2008) Modifying motor learning through gating and homeostatic metaplasticity. Brain Stimulation, 1, 60–66.