Journal Club (March 2, 2021)

Review articles
Hierarchy’ in the organization of brain networks
Claus C. Hilgetag and Alexandros Goulas (Institute of Computational Neuroscience, University Medical Center Eppendorf, Hamburg University, Hamburg, Germany)
Published:24 February 2020

Philosophical Transactions of the Royal Society B: Biological Sciences

*The Philosophical Transactions of the Royal Societyはイギリス王立協会の発行する学術論文誌である。『哲学紀要』と訳されることもある。1665年3月6日に創刊され、英語圏では最古のジャーナルである。(Wikipediaを参考)


Concepts shape the interpretation of facts. One of the most popular concepts in systems neuroscience is that of ‘hierarchy’. However, this concept has been interpreted in many different ways, which are not well aligned. This observation suggests that the concept is ill defined. Using the example of the organization of the primate visual cortical system, we explore several contexts in which ‘hierarchy’ is currently used in the description of brain networks. We distinguish at least four different uses, specifically, ‘hierarchy’ as a topological sequence of projections, as a gradient of features, as a progression of scales, or as a sorting of laminar projection patterns. We discuss the interpretation and functional implications of the different notions of ‘hierarchy’ in these contexts and suggest that more specific terms than ‘hierarchy’ should be used for a deeper understanding of the different dimensions of the organization of brain networks.

This article is part of the theme issue ‘Unifying the essential concepts of biological networks: biological insights and philosophical foundations’.


本論文は、テーマ「Unifying the essential concepts of biological networks: biological insights and philosophical foundations」の一部である。

Figure 6. Schematic of hierarchical multi-level modular network organization. This nested module-within-module architecture can comprise diverse types of networks, for example, with (left) or without (right) central hub nodes. The nodes are also differentiated by scales of network access, distinguishing nodes with global access (hub nodes) from local nodes. 

Figure 8. Overview of different concepts of ‘hierarchy’ in cortical brain networks as reviewed in the present paper. Depending on the chosen ‘hierarchy’ concept, the arrangement of the areas may vary substantially, also leading to different expectations of their functional properties. This overview is not exhaustive, and further notions of ‘hierarchy’ may be identified in the literature. (a) Sorting of areas by their ‘forward’ and ‘backward’ projections as classified from the laminar patterns of projection origins and terminations. (b) Arrangement of areas by the topological sequence of their connections, according to shortest paths from inputs at the bottom to outputs on the top. (c) Sorting of areas by feature gradients, for instance of cortical types or cellular density increasing from bottom to top. (d) Arrangement of areas by a progression of scales. Smaller neural systems are encapsulated in larger ones. For instance, laminar compartments are contained in cortical areas, which are in turn grouped into increasingly larger systems, such as the ventral and dorsal ‘streams’ of the primate visual system [73], by the arrangement of their connections and their functional properties. (Online version in colour.)


Ultimately, all the different aspects of ‘hierarchy’ are integrated through the embedding of connections in the spatial and topological architecture of the brain [30,72], where they underlie multiple interwoven structural and functional features that give rise to the intricate activity patterns and functions of the nervous system.


Human Brain Consisting Of Colored Wires Surrounded By Neural Threads. 3D Illustration.


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