Maltenfort M G, Heckman C J, Rymer W Z
Department of Biomedical Engineering, Northwestern University, Chicago, IL 60611, USA.
J Neurophysiol. 1998 Jul;80(1):309-23. doi: 10.1152/jn.1998.80.1.309.
A simulation of spinal motoneurons and Renshaw cells was constructed to examine possible functions of recurrent inhibition. Recurrent inhibitory feedback via Renshaw cells is known to be weak. In our model, consistent with this, motoneuron firing was only reduced by a few pulses per second. Our initial hypothesis was that Renshaw cells would suppress synchronous firings of motoneurons caused by shared, dynamic inputs. Each motoneuron received an identical pattern of noise in its input. Synchrony coefficients were defined as the average motoneuron population firing relative to the activity of selected reference motoneurons; positive coefficients resulted if the motoneuron population was particularly active at the same time the reference motoneuron was active. With or without recurrent inhibition, the motoneuron pools tended to show little if any synchronization. Recurrent inhibition was expected to reduce the synchrony even further. Instead, it reduced the variance of the synchrony coefficients, without a comparable effect on the average. This suggests-surprisingly-that both positive and negative correlations between motoneurons are suppressed by recurrent inhibition. In short, recurrent inhibition may operate as a negative feedback mechanism to decorrelate motoneurons linked by common inputs. A consequence of this decorrelation is the suppression of spectral activity that apparently arises from correlated motoneuron firings due to common excitatory drive. Without recurrent inhibition, the power spectrum of the total motoneuron pool firings showed a peak at a frequency corresponding to the largest measured firing rates of motoneurons in the pool. Recurrent inhibition either reduced or abolished this peak, presumably by minimizing the likelihood of correlated firing among pool elements. Renshaw cells may act to diminish physiological tremor, by removing oscillatory components from aggregate motoneuron activity. Recurrent inhibition also improved coherence between the aggregate motoneuron output and the common drive, at frequencies above the frequency of the "synchronous" peak. Sensitivity analyses demonstrated that the spectral effect became stronger as the duration of inhibitory synaptic conductance was shortened with either the magnitude or the spatial extent of the inhibitory conductances increased to maintain constant net inhibition. Overall, Renshaw inhibition appears to be a powerful way to adjust the dynamic behavior of a neuron population with minimal impact on its static gain.
构建了一个脊髓运动神经元和闰绍细胞的模拟模型，以研究回返抑制的可能功能。已知通过闰绍细胞的回返抑制性反馈较弱。在我们的模型中，与此一致的是，运动神经元的放电频率仅每秒降低几个脉冲。我们最初的假设是，闰绍细胞会抑制由共享的动态输入引起的运动神经元同步放电。每个运动神经元在其输入中接收到相同模式的噪声。同步系数定义为相对于选定参考运动神经元活动的平均运动神经元群体放电；如果运动神经元群体在参考运动神经元活动的同时特别活跃，则会得到正系数。无论有无回返抑制，运动神经元池几乎都没有表现出同步性。预计回返抑制会进一步降低同步性。相反，它降低了同步系数的方差，而对平均值没有类似影响。这令人惊讶地表明，运动神经元之间的正相关和负相关都受到回返抑制的抑制。简而言之，回返抑制可能作为一种负反馈机制，使由共同输入连接的运动神经元去相关。这种去相关的一个结果是抑制了显然由共同兴奋性驱动导致的相关运动神经元放电所产生的频谱活动。没有回返抑制时，总运动神经元池放电的功率谱在对应于池中运动神经元最大测量放电频率的频率处出现峰值。回返抑制要么降低要么消除了这个峰值，大概是通过最小化池元素之间相关放电的可能性。闰绍细胞可能通过消除总运动神经元活动中的振荡成分来减轻生理性震颤。在高于“同步”峰值频率的频率下，回返抑制还改善了总运动神经元输出与共同驱动之间的相干性。敏感性分析表明，随着抑制性突触电导持续时间缩短，且抑制性电导的幅度或空间范围增加以维持恒定的净抑制，频谱效应变得更强。总体而言，闰绍抑制似乎是一种强大的方式，可以在对神经元群体的静态增益影响最小的情况下调整其动态行为。
