Werhahn Konrad J, Mortensen Jennifer, Kaelin-Lang Alain, Boroojerdi Babak, Cohen Leonardo G
Human Cortical Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892-1428, USA.
Brain. 2002 Jun;125(Pt 6):1402-13. doi: 10.1093/brain/awf140.
Short-term deprivation of sensory input by ischaemic nerve block (INB) leads to functional reorganization in the deafferented motor cortex. Here, we show that INB also elicits functional changes in homotopic regions of the cortex contralateral to the deafferented one. We measured motor evoked potential (MEP) amplitudes elicited by transcranial magnetic stimulation (TMS) in small hand and biceps brachii muscles before, during and after INB of the right hand. INB increased excitability of the cortical representation of (i) the intact hand and (ii) body parts proximal to the deafferented hand (upper arm), in the absence of excitability changes in other body part representations such as thorax or leg muscles. This effect persisted throughout the entire period of deafferentation and returned to baseline values afterward. Motor responses to brainstem electrical stimulation remained unchanged during INB, indicating that the effect is probably of cortical origin. Lorazepam, a GABA(A) receptor agonist, blocked this increased excitability. Interhemispheric inhibition between hand muscles decreased during INB. After chronic deafferentation in amputees, MEP amplitudes and motor output curves in small hand muscles were depressed and motor thresholds were elevated compared with aged-matched controls. These results indicate that acute hand deafferentation can elicit a focal increase in excitability in the hand motor representation contralateral to the deafferented cortex that is influenced by transcallosal interactions and GABAergic transmission, and is balanced in the setting of chronic deafferentation.
通过缺血性神经阻滞（INB）短期剥夺感觉输入会导致去传入运动皮层的功能重组。在此，我们表明INB还会在与去传入侧相对的皮层同位区域引发功能变化。我们在右手进行INB之前、期间和之后，测量了经颅磁刺激（TMS）诱发的手部小肌肉和肱二头肌的运动诱发电位（MEP）幅度。INB增加了（i）未受影响的手部以及（ii）去传入手部（上臂）近端身体部位的皮层表征的兴奋性，而胸部或腿部肌肉等其他身体部位的表征兴奋性没有变化。这种效应在整个去传入期间持续存在，之后恢复到基线值。在INB期间，对脑干电刺激的运动反应保持不变，表明该效应可能源于皮层。GABA(A)受体激动剂劳拉西泮可阻断这种兴奋性增加。在INB期间，手部肌肉之间的半球间抑制减弱。与年龄匹配的对照组相比，截肢者长期去传入后，手部小肌肉的MEP幅度和运动输出曲线降低，运动阈值升高。这些结果表明，急性手部去传入可在与去传入皮层相对的手部运动表征中引发局部兴奋性增加，这种增加受胼胝体间相互作用和GABA能传递的影响，并且在慢性去传入情况下达到平衡。
