Börgers Christoph, Kopell Nancy
Department of Mathematics, Tufts University, Medford, MA 02155, U.S.A.
Neural Comput. 2003 Mar;15(3):509-38. doi: 10.1162/089976603321192059.
In model networks of E-cells and I-cells (excitatory and inhibitory neurons, respectively), synchronous rhythmic spiking often comes about from the interplay between the two cell groups: the E-cells synchronize the I-cells and vice versa. Under ideal conditions-homogeneity in relevant network parameters and all-to-all connectivity, for instance-this mechanism can yield perfect synchronization. We find that approximate, imperfect synchronization is possible even with very sparse, random connectivity. The crucial quantity is the expected number of inputs per cell. As long as it is large enough (more precisely, as long as the variance of the total number of synaptic inputs per cell is small enough), tight synchronization is possible. The desynchronizing effect of random connectivity can be reduced by strengthening the E --> I synapses. More surprising, it cannot be reduced by strengthening the I --> E synapses. However, the decay time constant of inhibition plays an important role. Faster decay yields tighter synchrony. In particular, in models in which the inhibitory synapses are assumed to be instantaneous, the effects of sparse, random connectivity cannot be seen.
在由E细胞和I细胞（分别为兴奋性和抑制性神经元）构成的模型网络中，同步节律性放电通常源于这两类细胞群之间的相互作用：E细胞使I细胞同步，反之亦然。在理想条件下，比如相关网络参数的同质性以及全连接性，这种机制能够产生完美同步。我们发现，即便连接非常稀疏且随机，近似的、不完美的同步也是可能的。关键量是每个细胞的预期输入数量。只要它足够大（更准确地说，只要每个细胞突触输入总数的方差足够小），紧密同步就是可能的。随机连接的去同步效应可以通过增强E→I突触来降低。更令人惊讶的是，增强I→E突触并不能降低这种效应。然而，抑制的衰减时间常数起着重要作用。更快的衰减会产生更紧密的同步。特别是，在假设抑制性突触是瞬时的模型中，稀疏、随机连接的效应是看不到的。
