The elusive concept of brain network. Comment on "Understanding brain networks and brain organization" by Luiz Pessoa.

As the poet John Donne said of man -“No man is an island entire of itself; every man is a piece of the continent, a part of the main.” - so the neuroscience research community now says of brain areas. This is the topic that Luiz Pessoa expands upon in his thorough review of the paradigm shift that has occurred in much of brain research, especially in cognitive neuroscience [1]. His key point is made explicitly in the Abstract: “I argue that a network perspective should supplement the common strategy of understanding the brain in terms of individual regions.” In his review, Pessoa covers a large range of topics, including how the network perspective changes the way in which one views the structure-function relationship between brain and behavior, the importance of context is ascertaining how a brain region functions, and the notion of emergent properties as a network feature. Also discussed is graph theory, one of the important mathematical methods used to analyze and describe network structure and function.