کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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6006248 | 1184678 | 2014 | 10 صفحه PDF | دانلود رایگان |
BackgroundTranscranial magnetic stimulation (TMS) of the human primary motor hand area (M1-HAND) can produce multiple descending volleys in fast-conducting corticospinal neurons, especially so-called indirect waves (I-waves) resulting from trans-synaptic excitation. Facilitatory interaction between these I-waves can be studied non-invasively using a paired-pulse paradigm referred to as short-interval intracortical facilitation (SICF).Objective/hypothesisWe examined whether SICF depends on waveform and current direction of the TMS pulses.MethodsIn young healthy volunteers, we applied single- and paired-pulse TMS to M1-HAND. We probed SICF by pairs of monophasic or half-sine pulses at suprathreshold stimulation intensity and inter-stimulus intervals (ISIs) between 1.0 and 5.0Â ms. For monophasic paired-pulse stimulation, both pulses had either a posterior-anterior (PA) or anterior-posterior (AP) current direction (AP-AP or PA-PA), whereas current direction was reversed between first and second pulse for half-sine paired-pulse stimulation (PA-AP and AP-PA).ResultsMonophasic AP-AP stimulation resulted in stronger early SICF at 1.4Â ms relative to late SICF at 2.8 and 4.4Â ms, whereas monophasic PA-PA stimulation produced SICF of comparable size at all three peaks. With half-sine stimulation the third SICF peak was reduced for PA-AP current orientation compared with AP-PA.ConclusionSICF elicited using monophasic as well as half-sine pulses is affected by current direction at clearly suprathreshold intensities. The impact of current orientation is stronger for monophasic compared with half-sine pulses. The direction-specific effect of paired-pulse TMS on the strength of early versus late SICF shows that different cortical circuits mediate early and late SICF.
Journal: Brain Stimulation - Volume 7, Issue 1, JanuaryâFebruary 2014, Pages 49-58