Zoghi Maryam, Pearce Sophie L, Nordstrom Michael A
Department of Physiology, University of Adelaide, Adelaide, SA 5005, Australia.
J Physiol. 2003 Aug 1;550(Pt 3):933-46. doi: 10.1113/jphysiol.2003.042606. Epub 2003 Jun 13.
Paired-pulse transcranial magnetic stimulation (TMS) was used to assess the effectiveness of intracortical inhibition (ICI) acting on corticospinal neurons controlling three intrinsic hand muscles in humans. We hypothesised that the suppression of ICI with selective activation of a muscle would be restricted to corticospinal neurons controlling the muscle targeted for activation. Surface EMG was recorded from abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles of the left hand. Subjects were tested at rest and during weak selective activation of APB or ADM, while they attempted to keep the other muscles relaxed using visual feedback. Paired-pulse TMS was applied with a circular coil oriented to produce antero-posterior (AP) current flow in the right motor cortex (to preferentially evoke I3 waves in corticospinal neurons) and with postero-anterior (PA) currents (to preferentially evoke I1 waves). Paired-pulse TMS was less effective in suppressing the muscle evoked potential (MEP) when the muscle was targeted for selective activation, with both AP and PA stimulation. The mechanism for this includes effects on late I waves, as it was evident with a weak AP test TMS pulse that elicited negligible I1 waves in corticospinal neurons. ICI circuits activated by TMS, which exert their effects on late I waves but do not affect I1 waves, are strongly implicated in this modulation. With AP stimulation, paired-pulse inhibition was not significantly altered for corticospinal neurons controlling other muscles of the same hand which were required to be inactive during the selective activation task. This differential modulation was not seen with PA stimulation, which preferentially activates I1 waves and evokes a MEP that is less influenced by ICI. The observations with AP stimulation suggest that selective activation of a hand muscle is accompanied by a selective suppression of ICI effects on the corticospinal neurons controlling that muscle. The pattern of differential modulation of ICI effectiveness with voluntary activation suggests that the ICI circuits assist the corticospinal system in producing fractionated activity of intrinsic hand muscles.
配对脉冲经颅磁刺激（TMS）被用于评估皮质内抑制（ICI）作用于控制人类手部三块固有肌肉的皮质脊髓神经元的有效性。我们假设，通过选择性激活一块肌肉来抑制ICI，将仅限于控制目标激活肌肉的皮质脊髓神经元。从左手的拇短展肌（APB）、第一背侧骨间肌（FDI）和小指展肌（ADM）记录表面肌电图。在静息状态以及APB或ADM进行弱选择性激活期间对受试者进行测试，同时他们利用视觉反馈试图使其他肌肉保持放松。采用圆形线圈施加配对脉冲TMS，线圈方向设置为在右侧运动皮层产生前后（AP）电流（以优先诱发皮质脊髓神经元中的I3波）以及后前（PA）电流（以优先诱发I1波）。当对肌肉进行选择性激活时，无论是AP刺激还是PA刺激，配对脉冲TMS在抑制肌肉诱发电位（MEP）方面效果均较差。其机制包括对晚期I波的影响，因为在皮质脊髓神经元中由弱AP测试TMS脉冲诱发可忽略不计的I1波时这一点很明显。由TMS激活的ICI回路对晚期I波发挥作用，但不影响I1波，强烈参与了这种调制。在AP刺激下，对于控制同一只手其他需要在选择性激活任务期间保持不活动的肌肉的皮质脊髓神经元，配对脉冲抑制没有显著改变。PA刺激未观察到这种差异调制，PA刺激优先激活I1波并诱发受ICI影响较小的MEP。AP刺激的观察结果表明，手部肌肉的选择性激活伴随着对控制该肌肉的皮质脊髓神经元上ICI效应的选择性抑制。ICI有效性随自愿激活的差异调制模式表明，ICI回路有助于皮质脊髓系统产生手部固有肌肉的分级活动。
