Brain structure and dynamics across scales: in search of rules

- We review recent work on mesoscopic, directed-connectivity and weighted-connectivity of monkey and rodent.
- New data led to the proposal of a spatially embedded random network model for the mammalian cortex.
- Several important differences between primate and rodent are highlighted.
- A large-scale dynamical model of the primate cortex gives rise to a hierarchy of timescales.

Louis Henry Sullivan, the father of skyscrapers, famously stated 'Form ever follows function'. In this short review, we will focus on the relationship between form (structure) and function (dynamics) in the brain. We summarize recent advances on the quantification of directed- and weighted-mesoscopic connectivity of mammalian cortex, the exponential distance rule for mesoscopic and microscopic circuit wiring, a spatially embedded random model of inter-areal cortical networks, and a large-scale dynamical circuit model of money's cortex that gives rise to a hierarchy of timescales. These findings demonstrate that inter-areal cortical networks are dense (hence such concepts as 'small-world' need to be refined when applied to the brain), spatially dependent (therefore purely topological approach of graph theory has limited applicability) and heterogeneous (consequently cortical areas cannot be treated as identical 'nodes').