Yuasa Akiko, Uehara Shintaro, Liu Boqun, Otaka Yohei
Department of Rehabilitation Medicine, Fujita Health University School of Medicine, Toyoake, Japan.
Japan Society for the Promotion of Science, Chiyodaku, Japan.
J Neurophysiol. 2025 Sep 1;134(3):866-874. doi: 10.1152/jn.00064.2025. Epub 2025 Aug 4.
The motor system continuously receives sensory inputs and uses this information to perform purposeful movements in a process known as sensorimotor integration. As a biomarker of sensorimotor integration efficacy, short-latency afferent inhibition (SAI), the phenomenon whereby afferent sensory inputs inhibit cortical motor outputs in a given muscle, has been widely studied in humans. However, it remains unclear how the (sensory) nerve-muscle relationship, that is, anatomical proximity and homotopy (nerve supply to muscles), affects SAI magnitude. To address this question, we assessed SAI magnitudes in cortical motor excitability by examining the size of the motor representations of two intrinsic hand muscles when afferent inputs were provided to the nerves either innervating or noninnervating the muscles. In 16 healthy adults, we measured the effect of conditioning electrical stimuli to the median nerve (MN) or ulnar nerve (UN) at the wrist on motor evoked potentials induced by transcranial magnetic stimulation in the first dorsal interosseous (innervated by UN) and abductor pollicis brevis (innervated by MN) muscles, both of which are anatomically located closer to MN than to UN. Conditioning MN stimulation resulted in a significant SAI in both muscles, with no significant difference in SAI between the muscles. No clear SAI was found in either muscle with the UN stimulation. These results suggest that SAI magnitude may depend on anatomical proximity rather than on homotopy. Given the inhibition of the motor representation size of both muscles, the specific nature of such SAI may contribute to the synergistic coordination between muscles. We found the significant SAI in both cortical broad (motor map) and local (hotspot) areas of the FDI and APB hand muscles only when a conditioning stimulus was delivered to the MN not to the UN. These results suggest that the SAI magnitude may depend on anatomical proximity rather than homotopic interactions between the nerve-muscle relationship, which may contribute to the synergistic coordination of muscles in response to afferent sensory inputs.
运动系统持续接收感觉输入，并利用这些信息在一个被称为感觉运动整合的过程中进行有目的的运动。作为感觉运动整合效能的生物标志物，短潜伏期传入抑制（SAI），即传入感觉输入抑制特定肌肉中皮质运动输出的现象，已在人类中得到广泛研究。然而，（感觉）神经 - 肌肉关系，即解剖学上的接近程度和同调性（肌肉的神经供应）如何影响SAI的大小仍不清楚。为了解决这个问题，我们通过检查当传入输入提供给支配或不支配这些肌肉的神经时，两块手部固有肌肉的运动代表区大小，来评估皮质运动兴奋性中的SAI大小。在16名健康成年人中，我们测量了手腕处正中神经（MN）或尺神经（UN）的条件电刺激对经颅磁刺激在第一背侧骨间肌（由UN支配）和拇短展肌（由MN支配）中诱发的运动诱发电位的影响，这两块肌肉在解剖学上都比尺神经更靠近正中神经。对正中神经进行条件刺激在两块肌肉中均导致显著的SAI，两块肌肉之间的SAI无显著差异。对尺神经进行刺激时，在两块肌肉中均未发现明显的SAI。这些结果表明，SAI大小可能取决于解剖学上的接近程度而非同调性。鉴于两块肌肉的运动代表区大小均受到抑制，这种SAI的具体性质可能有助于肌肉之间的协同协调。我们发现，仅当对正中神经而非尺神经施加条件刺激时，在FDI和APB手部肌肉的皮质广泛（运动图谱）和局部（热点）区域均出现显著的SAI。这些结果表明，SAI大小可能取决于解剖学上的接近程度，而非神经 - 肌肉关系之间的同位相互作用，这可能有助于肌肉在传入感觉输入时的协同协调。
