On the Connectivity in the Central Nervous System and the Age-Induced Changes of Its Network Organization

Intercellular communication plays a crucial role as the structural substrate for the brain functions. It occurs according to two main processes, namely wiring transmission, i.e. the transmission of signals through physical contacts between cells, and volume transmission, i.e. the chemical signal diffusion along the interstitial fluid pathways. Intercellular communication represents the main rationale for the emerging field of connectomics, defined as the comprehensive study of all aspects of central nervous system connectivity, aimed at creating a comprehensive map (connectome) of the cellular networks in the brain to better understand brain functions. A consensus exists that the brain connectome structure follows a hierarchical or nested architecture, and macro-, meso- and microscales have been defined. Available data on network organization at these different miniaturization levels will be here briefly reviewed. The connectome, however, is also a dynamical entity, undergoing changes during lifetime. Thus, a specific focus will be maintained on the changes the network organization undergoes during normal aging.