Chklovskii Dmitri B, Stepanyants Armen
Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
BMC Neurosci. 2003 Aug 28;4:18. doi: 10.1186/1471-2202-4-18.
Axon calibers vary widely among different animals, neuron classes, and even within the same neuron. What determines the diameter of axon branches?
We pursue the hypothesis that the axon caliber has evolved to minimize signal propagation delays, while keeping arbor volume to a minimum. For a general cost function, we show that the optimal diameters of mother and daughter branches at a bifurcation satisfy a power law. The derivation relies on the fact that the axon conduction speed scales as a power of axon diameter. Although available data are consistent with the law, there is a large spread in the data. Future experimental tests will determine whether this spread is due to biological variability or measurement error.
Minimization of arbor volume and signal propagation delay may have been an important factor in the evolution of the brain.
轴突直径在不同动物、不同神经元类别之间，甚至在同一神经元内部都存在很大差异。是什么决定了轴突分支的直径？
我们探究了这样一种假说，即轴突直径的进化是为了在将树突体积保持在最小的同时，使信号传播延迟最小化。对于一个一般的代价函数，我们表明在分叉处母分支和子分支的最优直径满足幂律。该推导依赖于轴突传导速度与轴突直径的幂成正比这一事实。尽管现有数据与该定律一致，但数据存在很大的离散度。未来的实验测试将确定这种离散是由于生物学变异性还是测量误差。
树突体积和信号传播延迟的最小化可能是大脑进化中的一个重要因素。
