Hofstoetter Ursula S, Danner Simon M, Freundl Brigitta, Binder Heinrich, Mayr Winfried, Rattay Frank, Minassian Karen
Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria;
Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; Institute of Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria; and.
J Neurophysiol. 2015 Jul;114(1):400-10. doi: 10.1152/jn.00136.2015. Epub 2015 Apr 22.
In individuals with motor-complete spinal cord injury, epidural stimulation of the lumbosacral spinal cord at 2 Hz evokes unmodulated reflexes in the lower limbs, while stimulation at 22-60 Hz can generate rhythmic burstlike activity. Here we elaborated on an output pattern emerging at transitional stimulation frequencies with consecutively elicited reflexes alternating between large and small. We analyzed responses concomitantly elicited in thigh and leg muscle groups bilaterally by epidural stimulation in eight motor-complete spinal cord-injured individuals. Periodic amplitude modulation of at least 20 successive responses occurred in 31.4% of all available data sets with stimulation frequency set at 5-26 Hz, with highest prevalence at 16 Hz. It could be evoked in a single muscle group only but was more strongly expressed and consistent when occurring in pairs of antagonists or in the same muscle group bilaterally. Latencies and waveforms of the modulated reflexes corresponded to those of the unmodulated, monosynaptic responses to 2-Hz stimulation. We suggest that the cyclical changes of reflex excitability resulted from the interaction of facilitatory and inhibitory mechanisms emerging after specific delays and with distinct durations, including postactivation depression, recurrent inhibition and facilitation, as well as reafferent feedback activation. The emergence of large responses within the patterns at a rate of 5.5/s or 8/s may further suggest the entrainment of spinal mechanisms as involved in clonus. The study demonstrates that the human lumbosacral spinal cord can organize a simple form of rhythmicity through the repetitive activation of spinal reflex circuits.
在运动完全性脊髓损伤患者中，以2Hz频率对腰骶部脊髓进行硬膜外刺激可诱发下肢无调制反射，而以22 - 60Hz频率刺激则可产生节律性爆发样活动。在此，我们阐述了在过渡刺激频率下出现的一种输出模式，即连续诱发的反射在大小之间交替。我们分析了8例运动完全性脊髓损伤患者在硬膜外刺激时双侧大腿和腿部肌肉群同时诱发的反应。在所有可用数据集中，31.4%的数据在刺激频率设定为5 - 26Hz时出现了至少20次连续反应的周期性幅度调制，其中在16Hz时发生率最高。这种调制仅在单个肌肉群中可诱发，但当在拮抗肌对或双侧同一肌肉群中出现时，表达更强且更一致。调制反射的潜伏期和波形与对2Hz刺激的未调制单突触反应的潜伏期和波形相对应。我们认为，反射兴奋性的周期性变化是由特定延迟和不同持续时间后出现的易化和抑制机制相互作用导致的，包括激活后抑郁、反复抑制和易化，以及再传入反馈激活。模式中以5.5/s或8/s的速率出现大反应可能进一步表明参与阵挛的脊髓机制的同步化。该研究表明，人类腰骶部脊髓可通过脊髓反射回路的重复激活来组织一种简单的节律形式。
