Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark.
Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark; Department of Neurology, Copenhagen University Hospital Bispebjerg and Frederiksberg, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
Neuroimage. 2022 Sep;258:119365. doi: 10.1016/j.neuroimage.2022.119365. Epub 2022 Jun 9.
Transcranial magnetic stimulation (TMS) is widely used to probe corticospinal excitability and fast sensorimotor integration in the primary motor hand area (M1-HAND). A conditioning electrical stimulus, applied to the contralateral hand, can suppress the motor evoked potential (MEP) elicited by TMS of M1-HAND when the afferent stimulus arrives in M1-HAND at the time of TMS. The magnitude of this short-latency afferent inhibition (SAI) is expressed as the ratio between the conditioned and unconditioned MEP amplitude.
OBJECTIVE/HYPOTHESIS: We hypothesized that corticospinal excitability and SAI are influenced by the recent history of peripheral electrical stimulation.
In twenty healthy participants, we recorded MEPs from the right first dorsal interosseus muscle. MEPs were evoked by single-pulse TMS of the left M1-HAND alone (unconditioned TMS) or by TMS preceded by electrical stimulation of the right index finger ("homotopic" conditioning) or little finger ("heterotopic" conditioning). The three conditions were either pseudo-randomly intermixed or delivered in blocks in which a single condition was repeated five or ten times. MEP amplitudes and SAI magnitudes were compared using linear mixed-effect models and one-way ANOVAs.
All stimulation protocols consistently produced SAI, which was stronger after homotopic stimulation. Randomly intermingling the three stimulation conditions reduced the relative magnitude of homotopic and heterotopic SAI as opposed to blocked stimulation. The apparent attenuation of SAI was caused by a suppression of the unconditioned but not the conditioned MEP amplitude during the randomly intermixed pattern.
CONCLUSION(S): The recent history of afferent stimulation modulates corticospinal excitability. This "history effect" impacts on the relative magnitude of SAI depending on how conditioned and unconditioned responses are intermixed and needs to be taken into consideration when probing afferent inhibition and corticospinal excitability.
经颅磁刺激（TMS）广泛用于探测初级运动手区（M1-HAND）中的皮质脊髓兴奋性和快速感觉运动整合。当刺激传入 M1-HAND 与 TMS 同时到达时，施加于对侧手的条件性电刺激可抑制 TMS 诱发的运动诱发电位（MEP）。这种短潜伏期传入抑制（SAI）的幅度表示为条件和非条件 MEP 幅度的比值。
目的/假设：我们假设皮质脊髓兴奋性和 SAI 受近期外周电刺激的影响。
在二十名健康参与者中，我们记录了右侧第一背侧骨间肌的 MEP。通过单独刺激左侧 M1-HAND 产生单脉冲 TMS 诱发 MEP（未条件刺激 TMS）或在右侧食指（“同源”条件刺激）或小指（“异源”条件刺激）刺激之前进行 TMS 诱发 MEP。这三种条件以随机或块的方式混合，其中单个条件重复五次或十次。使用线性混合效应模型和单向方差分析比较 MEP 幅度和 SAI 幅度。
所有刺激方案均一致产生 SAI，同源刺激后 SAI 更强。与块刺激相比，随机混合三种刺激条件会降低同源和异源 SAI 的相对幅度。SAI 的明显衰减是由于在随机混合模式下未条件 MEP 幅度的抑制而不是条件 MEP 幅度的抑制引起的。
传入刺激的近期历史会调节皮质脊髓兴奋性。这种“历史效应”会影响 SAI 的相对幅度，具体取决于条件和非条件反应的混合方式，在探测传入抑制和皮质脊髓兴奋性时需要考虑到这一点。
