Tamburin Stefano, Fiaschi Antonio, Andreoli Annalisa, Marani Silvia, Zanette Giampietro
Department of Neurological Sciences and Vision, Section of Neurological Rehabilitation, University of Verona, Verona, Italy.
Exp Brain Res. 2005 Dec;167(3):362-9. doi: 10.1007/s00221-005-0041-y. Epub 2005 Aug 3.
Transcranial magnetic stimulation (TMS) can be used to study sensorimotor integration in humans non-invasively. Motor excitability has been found to be inhibited when afferent stimuli are given to a peripheral nerve and precede TMS at interstimulus intervals (ISIs) of 20-50 ms. This phenomenon has been referred to as short-latency afferent inhibition (SAI). To better understand the functional meaning of these phenomena, we examined the effect of the size of the receptive field on SAI to cutaneous afferents in upper-limb sensorimotor areas in humans. We examined the effect of the stimulation of the isolated right first (D1), second (D2) and third finger (D3), the right second and third finger together (D23) and the right first three fingers together (D123) on the amplitude of motor evoked potentials (MEPs) to TMS in hand and forearm muscles. We examined the right abductor pollicis brevis (APB), first dorsal interosseous (FDI), extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscles. Digital stimulation preceded TMS at ISIs of 20-50 ms. The effect of D2 stimulation was MEP inhibition (SAI), which was more marked and consistent in APB and FDI muscles than in ECR and FCR muscles. Similarly, D1 and D3 stimulation caused MEP reduction, while no MEP enhancement could be found to single finger stimulation. In contrast, D123 stimulation induced less effective SAI in upper-limb muscles. MEP potentiation was recorded in some muscles to D123 stimulation. A significant difference between D2 and D123 stimulation was found in APB (ISIs = 30-50 ms) and FDI (ISIs = 40-50 ms) muscles, but not in forearm muscles. The effect to D23stimulation on MEP amplitude was intermediate between those to D2 and D123 stimulation. Our data suggest that motor excitability to cutaneous afferents may be influenced by the size of the receptive fields, this effect being the result of increasing convergence between hand afferents in the somatosensory system. These phenomena appear to be topographically arranged across the representation of upper-limb muscles. These findings may help to understand the functional significance of SAI in normal physiology and pathophysiology.
经颅磁刺激（TMS）可用于非侵入性地研究人类的感觉运动整合。当在20 - 50毫秒的刺激间隔（ISI）下，在经颅磁刺激（TMS）之前对外周神经给予传入刺激时，已发现运动兴奋性受到抑制。这种现象被称为短潜伏期传入抑制（SAI）。为了更好地理解这些现象的功能意义，我们研究了感受野大小对人类上肢感觉运动区域皮肤传入神经的短潜伏期传入抑制（SAI）的影响。我们研究了对孤立的右手食指（D1）、中指（D2）和无名指（D3）、右手食指和中指一起（D23）以及右手前三指一起（D123）的刺激对手部和前臂肌肉中经颅磁刺激（TMS）诱发的运动诱发电位（MEP）幅度的影响。我们研究了右手拇短展肌（APB）、第一背侧骨间肌（FDI）、桡侧腕伸肌（ECR）和桡侧腕屈肌（FCR）。在20 - 50毫秒的刺激间隔（ISI）下，数字刺激先于经颅磁刺激（TMS）。D2刺激的效果是运动诱发电位（MEP）抑制（SAI），在拇短展肌（APB）和第一背侧骨间肌（FDI）中比在桡侧腕伸肌（ECR）和桡侧腕屈肌（FCR）中更明显且更一致。同样，D1和D3刺激导致运动诱发电位（MEP）降低，而对单指刺激未发现运动诱发电位（MEP）增强。相比之下，D123刺激在上肢肌肉中诱发的短潜伏期传入抑制（SAI）效果较差。在一些肌肉中记录到对D123刺激的运动诱发电位（MEP）增强。在拇短展肌（APB，刺激间隔 = 30 - 50毫秒）和第一背侧骨间肌（FDI，刺激间隔 = 40 - 50毫秒）中发现D2和D123刺激之间存在显著差异，但在前臂肌肉中未发现。D23刺激对运动诱发电位（MEP）幅度的影响介于D2和D123刺激之间。我们的数据表明，对皮肤传入神经的运动兴奋性可能受感受野大小的影响，这种影响是体感系统中手部传入神经之间汇聚增加的结果。这些现象似乎在上肢肌肉的代表区域中按地形排列。这些发现可能有助于理解短潜伏期传入抑制（SAI）在正常生理和病理生理中的功能意义。
