Development

Studying the human brain during early development faces a variety of challenges, such as poor data quality due to movement, small head sizes and the lack of a standard scheme for defining regions of interest in the brain. Nonetheless, studying the developing brain using network theory is of great interest as it is important to characterise the "normal" developmental trajectory. This will ultimately help with the detection and diagnosis of pathological development and diseases at an early stage.

In general it has been shown that the developing human brain shows interesting characteristics, such as an asymmetry between the left and right hemisphere in respect to their network measures, as well as differences related to the sex of the subject. The results for the latter are still inconclusive as there are only a few studies focusing on that particular aspect, but studies suggest that females have a higher efficiency, as well as a higher clustering coefficient, resulting in a more pronounced small-world topology compared to males.

It has been suggested that brain networks develop from a local to distributed organisation. Long-distance connections are generally rare in biological networks. However, they allow for short-cuts within the network and are essential for efficient information transport. Starting from a local anatomical network, the architecture becomes more distributed during development, evolving from a more segregated to a more integrated network structure.

Both small-world and rich-club architecture can be found in the developing brain at an early age. Studies agree on the existence of small-world topology in neural networks over all developmental stages, however, the efficiency increases with age. This is most likely due to the myelination process within the brain, which allows the impulse propagation speed to increase. Additionally, Ball and colleagues showed that the rich-club organisation is present in children by 30 weeks of age and already precedes complex neurological function. However, feeder and local connections were still developing.