"Just as advanced mammalian brains require a robust neural network to achieve richer and more complex thought, large cities require advanced highways and transportation systems to allow larger and more productive populations. The new study unearthed a striking similarity in how larger brains and cities deal with the difficult problem of maintaining sufficient interconnectedness."
The internal infrastructures of both brains and cities were shown to scale up as they increase in size -- for example, a human brain will have more infrastructure than a dog brain, and Chicago (227.1 sq. miles) has more infrastructure than Seattle (83.9 sq. miles).
Thanks to The Infrastructurist