The Institute of Mathematical Sciences, Chennai, Tamil Nadu, India.
PLoS One. 2010 Feb 22;5(2):e9240. doi: 10.1371/journal.pone.0009240.
One of the biggest challenges in biology is to understand how activity at the cellular level of neurons, as a result of their mutual interactions, leads to the observed behavior of an organism responding to a variety of environmental stimuli. Investigating the intermediate or mesoscopic level of organization in the nervous system is a vital step towards understanding how the integration of micro-level dynamics results in macro-level functioning. The coordination of many different co-occurring processes at this level underlies the command and control of overall network activity. In this paper, we have considered the somatic nervous system of the nematode Caenorhabditis elegans, for which the entire neuronal connectivity diagram is known. We focus on the organization of the system into modules, i.e., neuronal groups having relatively higher connection density compared to that of the overall network. We show that this mesoscopic feature cannot be explained exclusively in terms of considerations such as, optimizing for resource constraints (viz., total wiring cost) and communication efficiency (i.e., network path length). Even including information about the genetic relatedness of the cells cannot account for the observed modular structure. Comparison with other complex networks designed for efficient transport (of signals or resources) implies that neuronal networks form a distinct class. This suggests that the principal function of the network, viz., processing of sensory information resulting in appropriate motor response, may be playing a vital role in determining the connection topology. Using modular spectral analysis we make explicit the intimate relation between function and structure in the nervous system. This is further brought out by identifying functionally critical neurons purely on the basis of patterns of intra- and inter-modular connections. Our study reveals how the design of the nervous system reflects several constraints, including its key functional role as a processor of information.
生物学面临的最大挑战之一是理解神经元在细胞水平上的活动如何通过它们的相互作用导致生物体对各种环境刺激做出观察到的反应。研究神经系统的中间或中观组织水平是理解微观水平动态如何导致宏观水平功能的关键步骤。在这个水平上，许多不同的同时发生的过程的协调是整个网络活动的指挥和控制的基础。在本文中，我们考虑了线虫秀丽隐杆线虫的躯体神经系统，因为它的整个神经元连接图是已知的。我们专注于系统组织成模块，即神经元组与整个网络相比具有相对较高的连接密度。我们表明，这种中观特征不能仅根据优化资源约束（即总布线成本）和通信效率（即网络路径长度）等考虑来解释。即使包括关于细胞遗传相关性的信息也不能解释观察到的模块结构。与其他为有效传输（信号或资源）而设计的复杂网络进行比较表明，神经元网络形成了一个独特的类别。这表明网络的主要功能，即处理感官信息以产生适当的运动反应，可能在确定连接拓扑结构方面起着至关重要的作用。使用模块谱分析，我们明确了神经系统中功能和结构之间的密切关系。通过仅基于内模块和模块间连接模式识别功能关键神经元，进一步阐明了这一点。我们的研究揭示了神经系统的设计如何反映出多种约束，包括其作为信息处理器的关键功能作用。
