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Similar Networks Are Needed In Growing Cities and Brains

Posted By Prucia Buscell, Thursday, September 10, 2009
Updated: Thursday, February 17, 2011
Dense interconnectedness is critical to the evolution and growth of both brains and cities, according to a new research by scientists at Rensselaer Polytechnic Institute.

The study, described on the Rensselaer website and in a story at, found surprising similarities in the way big cities and big brains maintain sufficient interconnectedness. Mark Changizi, a neurobiologist at Rensselaer who led the study, explains: "Natural selection has passively guided the evolution of mammalian brains through out time, just as politicians and entrepreneurs, have indirectly shaped the organization of cities large and small. It seems both of these 'invisible hands' have arrived at a similar conclusion: brains and cities, as they grow larger, have to be similarly densely interconnected to function properly."

Changizi and coauthor Marc Destefano, a clinical assistant professor in cognitive science at Rensselaer, report their findings in "Common Scaling Laws for City Highway Systems and the Mammalian Neocortex", publishedin the journal Complexity.

The authors explain one could not simply combine two dog brains and expectto have something that functions as a human brain, because the human brain doesn't just have more cells, it has more connections among the cells. In the same way, three Seattles combined wouldn'tfunction like a Chicago, even though the area would be the same. There would be too many highways with too few exits and lanes that were too narrow.

The researchers say when scaling up in size and function, brains and cities seem to follow similar empirical laws. As cities and the neocortex-the thinking region of the brain-grow in surface area, the number of connections scale to the 3/4 power. For cities, that means highways and in brains it's a type of closely interconnected cells called pyramidal neurons. In brains and cities, the number of highway exits and synapses, which have similar function as terminal points along highways and neurons, increase with an exponent of 9/8. The 3/4 power law is famous among math mavens. Click here for an explanation by physicist Brad Roth. Melanie Mitchell also discusses the phenomenon clearly in "The Mystery of Scaling", which is Chapter 17 of her book Complexity, a Guided Tour.

Visit Changizi's website for more information about his research and his new book, The Vision Revolution: How the Latest Research Overturns Everything We Thought We Knew About Human Vision.

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