1 Department of Dentistry and Oral Health - Section of Orofacial Pain and Jaw Function, Department of Dentistry and Oral Health, Health, Aarhus University2 Department of Clinical Medicine - Regionshospital Hammel Neurocenter, Department of Clinical Medicine, Health, Aarhus University3 Regionshospital Hammel Neurocenter, Faculty of Health Sciences, Aarhus University, Aarhus University4 Department of Clinical Medicine - Regionshospital Hammel Neurocenter, Department of Clinical Medicine, Health, Aarhus University5 Department of Dentistry and Oral Health - Section of Orofacial Pain and Jaw Function, Department of Dentistry and Oral Health, Health, Aarhus University
Objectives: Paired pulse transcranial magnetic stimulation (ppTMS) can be used to assess short-term interval intra-cortical inhibitory (SICI) and facilitatory (ICF) networks. The degree of SICI and ICF varies with interstimulus intervals (ISI) and stimulus intensities of the conditioning stimulus (CS) and the test stimulus (TS). The aim of the present methodological study was to optimize stimulus parameters for ppTMS studies of tongue motor control by examining the influence of different ISI and intensities of the CS on SICI and ICF. Methods: 17 healthy volunteers participated (mean age: 22.6±0.8 years). ppTMS was applied to the “hot-spot” of the tongue motor cortex and motor evoked potential (MEPs) were recorded from the tongue muscles with surface EMG electrodes. TS intensity was set at 120% of resting motor threshold (rMT). Single pulse and six different ISIs for ppTMS: 2, 2.5, 3, 3.5, 10, 15 ms were applied 8 times each in randomized order in two blocks (CS intensity of 70% and 80% of rMT, respectively). The amplitudes of the averaged MEPs were analyzed with analysis of variance. Results: There was an overall effect of ISI (P<0.001) but no significant difference between the two CS intensities (P = 0.984). Post-hoc tests revealed that there was significant SICI with ppTMS ISI of 2, 2.5, 3, and 3.5 ms compared with single pulse stimulation (P<0.003). There was no significant ICF with ISI of 10 or 15 ms compared with single pulse stimulation (P=0.988). There was no interaction between different intensities of CS and ISIs. Conclusion: Significant SICI but no ICF was evoked with the present stimulus paradigms. The two stimulus intensities of the CS evoked similar responses. These results may be applied in future studies on the effect of tongue training on SICI and ICF in the tongue motor cortex. Acknowledgments: Supported by the Danish Dental Association.