The connected brain

The connected brain Martijn van den Heuvel, 2009 Our brain is a network. It is a network of different brain regions that are all functionally and structurally linked to each other. In the past decades, neuroimaging studies have provided a lot of information about the specific functions of each separate brain region, but how functional communication between brain regions is organized remains largely unexplored. How is functional communication within the brain network organized? The concept of a brain network is not that different from networks we encounter in everyday life, like for example flight grids. Airports are linked to each other by flight routes and when traveling from Amsterdam to San Francisco it is much more efficient to have a direct flight, rather than to fly from Amsterdam to New York first and then from New York to San Francisco. In this thesis we explore the overall organization of functional communication channels in the brain and show that the human brain is organized according to one of the most efficient topologies that nature has to offer. We examine which specific brain regions communicate to each other and how they form sub-networks within the overall network. But how is functional communication between these anatomically separated brain region possible? We examine the structural core of functionally linked networks, examining whether functional connectivity overlaps with structural information highways. Our brain is a very efficient network. But how is this level of efficiency related to our cognitive performance? In thesis, we show that the level of global organization of the brain network is directly related to intellectual performance. Using graph analysis, we show that the most efficient brain networks belong the most intelligent people. Our findings suggest that intelligence is not related to the total amount of connectivity, but more to how efficient functional connections are placed between brain regions. As such, our findings suggest that intelligence may not be pinpointed to one particular brain region, but that it may be a property of the entire brain network.