Rossi S, Pasqualetti P, Tecchio F, Sabato A, Rossini P M
AFaR-Ospedale Fatebenefratelli-Isola Tiberina, Rome, 00136, Italy.
Neuroimage. 1998 Aug;8(2):163-75. doi: 10.1006/nimg.1998.0352.
Excitability and conductivity of corticospinal tracts of 10 volunteers were investigated by motor-evoked potentials (MEPs) to transcranial magnetic brain stimulation, before and after anesthetic block of right median (sensory + motor) and radial (sensory) nervous fibers at the wrist. MEPs were simultaneously recorded from two ulnar-supplied muscles during full relaxation and voluntary contraction. These muscles maintained an intact strength following anesthesia, but they were in a remarkably different condition with respect to the surrounding skin: the first dorsal interosseous muscle (FDI) was totally "enveloped" within the anesthetized area but was still dispatching a normal proprioceptive feedback; the abductor digiti minimi (ADM) was preserving both cutaneous and proprioceptive information. Spinal and peripheral nerve excitability were monitored as well. The sensory deprivation induced short-term changes which selectively took place within the hemisphere connected to the anesthetized hand. The physiological latency "anticipation" of MEPs recorded during active contraction versus relaxation was reduced (P < 0.001) in the FDI, but not in the ADM, when values during anesthesia were compared with preanesthesia values. The FDI cortical representation-as analyzed by a mapping procedure of the motor cortex via focal stimuli of several scalp positions-was significantly (P < 0.002) reduced, while the ADM representation remained either unchanged or enlarged. MEP and F-wave variability significantly decreased in the FDI but not in the ADM. F-waves were also affected due to changes in the motoneuronal excitability at spinal level. Peripheral nerve and root stimulation showed no modifications. Results are discussed in view of the short-term modifications of the corticospinal pathway somatotopy produced by the selective reduction of the sensory flow. Implications of the sensory feedback in motor control are also discussed.
在对10名志愿者手腕处的右侧正中神经（感觉 + 运动）和桡神经（感觉）纤维进行麻醉阻滞前后，通过经颅磁脑刺激诱发的运动诱发电位（MEP）来研究皮质脊髓束的兴奋性和传导性。在完全放松和自主收缩期间，同时从两块由尺神经支配的肌肉记录MEP。这些肌肉在麻醉后仍保持完整的力量，但它们与周围皮肤的状态明显不同：第一背侧骨间肌（FDI）完全“包裹”在麻醉区域内，但仍能传递正常的本体感觉反馈；小指展肌（ADM）则保留了皮肤感觉和本体感觉信息。同时也监测了脊髓和周围神经的兴奋性。感觉剥夺引起了短期变化，这些变化选择性地发生在与麻醉手相连的半球内。当将麻醉期间的值与麻醉前的值进行比较时，FDI在主动收缩与放松期间记录的MEP的生理潜伏期“预期”缩短（P < 0.001），而ADM则没有。通过对运动皮层进行多个头皮位置的局灶性刺激的映射程序分析，FDI的皮质代表区域显著缩小（P < 0.002），而ADM的代表区域则保持不变或扩大。FDI中MEP和F波的变异性显著降低，而ADM中则没有。由于脊髓水平运动神经元兴奋性的变化，F波也受到了影响。周围神经和神经根刺激未显示出改变。鉴于感觉输入选择性减少导致的皮质脊髓通路躯体定位的短期改变，对结果进行了讨论。还讨论了感觉反馈在运动控制中的意义。
