Pitkänen Minna, Kallioniemi Elisa, Julkunen Petro
Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland.
Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland.
PLoS One. 2017 Jul 19;12(7):e0181663. doi: 10.1371/journal.pone.0181663. eCollection 2017.
Repetition suppression (RS) is evident as a weakened response to repeated stimuli after the initial response. RS has been demonstrated in motor-evoked potentials (MEPs) induced with transcranial magnetic stimulation (TMS). Here, we investigated the effect of inter-train interval (ITI) on the induction of RS of MEPs with the attempt to optimize the investigative protocols. Trains of TMS pulses, targeted to the primary motor cortex by neuronavigation, were applied at a stimulation intensity of 120% of the resting motor threshold. The stimulus trains included either four or twenty pulses with an inter-stimulus interval (ISI) of 1 s. The ITI was here defined as the interval between the last pulse in a train and the first pulse in the next train; the ITIs used here were 1, 3, 4, 6, 7, 12, and 17 s. RS was observed with all ITIs except with the ITI of 1 s, in which the ITI was equal to ISI. RS was more pronounced with longer ITIs. Shorter ITIs may not allow sufficient time for a return to baseline. RS may reflect a startle-like response to the first pulse of a train followed by habituation. Longer ITIs may allow more recovery time and in turn demonstrate greater RS. Our results indicate that RS can be studied with confidence at relatively short ITIs of 6 s and above.
重复抑制（RS）表现为在初始反应后对重复刺激的反应减弱。重复抑制已在经颅磁刺激（TMS）诱发的运动诱发电位（MEP）中得到证实。在此，我们研究了串间间隔（ITI）对MEP重复抑制诱导的影响，试图优化研究方案。通过神经导航将TMS脉冲串靶向初级运动皮层，以静息运动阈值的120%的刺激强度施加。刺激串包括四个或二十个脉冲，刺激间隔（ISI）为1秒。这里的ITI定义为一串中的最后一个脉冲与下一串中的第一个脉冲之间的间隔；这里使用的ITI为1、3、4、6、7、12和17秒。除了ITI为1秒（此时ITI等于ISI）外，在所有ITI下均观察到重复抑制。ITI越长，重复抑制越明显。较短的ITI可能没有足够的时间恢复到基线。重复抑制可能反映了对一串中的第一个脉冲的类似惊吓的反应，随后是习惯化。较长的ITI可能允许更多的恢复时间，进而表现出更大的重复抑制。我们的结果表明，可以在6秒及以上的相对较短的ITI下可靠地研究重复抑制。
