Beck Sandra, Richardson Sarah Pirio, Shamim Ejaz A, Dang Nguyet, Schubert Martin, Hallett Mark
Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1428, USA.
J Neurosci. 2008 Oct 8;28(41):10363-9. doi: 10.1523/JNEUROSCI.3564-08.2008.
In patients with focal hand dystonia (FHD), pathological overflow activation occurs in muscles not involved in the movement. Surround inhibition is a neural mechanism that can sharpen desired movement by inhibiting unwanted movement in adjacent muscles. To further establish the phenomenon of surround inhibition and to determine whether short intracortical inhibition (SICI) reflecting inhibition from the local interneurons in primary motor cortex (M1), might play a role in its genesis, single- and paired-pulse transcranial magnetic stimulation (TMS), and Hoffmann reflex testing were applied to evaluate the excitability of the relaxed abductor pollicis brevis muscle (APB) at various intervals during a movement of the index finger in 16 patients with FHD and 20 controls. Whereas controls showed inhibition of APB motor-evoked potential (MEP) size during movement initiation and facilitation of APB MEP size during the maintenance phase, FHD patients did not modulate APB MEP size. In contrast, SICI remained constant in controls, but FHD patients showed reduced SICI during movement initiation. The H(max)/M(max) ratio in control subjects increased during movement initiation. The results provide additional evidence for the presence of surround inhibition in M1, where it occurs only during movement initiation, indicating that different mechanisms underlie movement initiation and maintenance. Thus, surround inhibition is sculpted both in time and space and may be an important neural mechanism during movement initiation to counteract increased spinal excitability. SICI may contribute to its generation, because in patients with FHD, the lack of depression of APB MEP size is accompanied by a reduction in SICI.
在患有局灶性手部肌张力障碍（FHD）的患者中，病理溢出激活发生在未参与运动的肌肉中。周围抑制是一种神经机制，可通过抑制相邻肌肉中不必要的运动来增强所需运动。为了进一步证实周围抑制现象，并确定反映初级运动皮层（M1）中局部中间神经元抑制作用的短皮质内抑制（SICI）是否可能在其发生过程中起作用，对16例FHD患者和20名对照者在食指运动的不同间隔期间应用单脉冲和双脉冲经颅磁刺激（TMS）以及霍夫曼反射测试，以评估放松状态下拇短展肌（APB）的兴奋性。对照组在运动起始阶段显示APB运动诱发电位（MEP）大小受到抑制，而在维持阶段APB MEP大小得到促进，而FHD患者并未调节APB MEP大小。相反，对照组的SICI保持恒定，但FHD患者在运动起始阶段显示SICI降低。对照组受试者的H(max)/M(max)比值在运动起始阶段增加。这些结果为M1中存在周围抑制提供了额外证据，周围抑制仅在运动起始阶段出现，表明运动起始和维持的机制不同。因此，周围抑制在时间和空间上都受到塑造，可能是运动起始阶段抵消脊髓兴奋性增加的重要神经机制。SICI可能有助于其产生，因为在FHD患者中，APB MEP大小缺乏抑制伴随着SICI的降低。
