Big news from small world networks after stroke

How does the brain accomplish any of its tasks? Each ‘bit’ of the brain receives a piece of information, performs a specific calculation on it, and forwards the processed information on to the next bit. Communication is crucial and needs to take place between different bits of the brain located near and far. Somehow, from local processing and functioning interconnections a thought, sensation or motor command emerges. The brain is a complex network comprising multiple ‘nodes’ and ‘links’, and the notion that only one place in the brain is responsible for anything amounts to phrenology. Nodes (also termed ‘vertices’) in large-scale neuronal networks usually represent anatomical regions. Links (also termed ‘edges’) represent functional or effective connections. The brain requires an optimal balance between regional segregation and inter-regional, global integration of neuronal activity. Measures are now available to give summary descriptions of the network structure.In order to understand pathological states of the brain therefore, it seems critical to determine what happens to brain network structure and function. In this issue of Brain, Wang et al. (2010) present an interesting set of data on reorganization of the motor executive network in patients suffering from subcortical stroke. This study is particular in that the authors focused on changes of network dynamics during the recovery process, rather than describing local activation phenomena only. Wang and colleagues used a longitudinal approach with follow-up testing at 1 week, 2 weeks, 1 month, 3 months and 1 year after stroke. The main finding is that the network does change, and the reorganized network gradually deviates more and more from what might be considered optimal network architecture. In the process of recovery, the global motor executive network with 21 predefined regions of interest becomes less ‘clustered’ and shows less functional segregation overall. However, within this less clustered …