10.2 Structural Dynamics
The previous section described the topology and spatial organization of neural systems. The structure of neural systems, however, can change over time. First, edges or nodes of the network could be removed. This can occur either due to learning or cell death (apoptosis) or to head injuries or strokes affecting fiber tracts or cortical tissue. Second, the network structure changes during neural development. Whereas development consists of both the formation of network connections and the loss of connections, especially in the pruning phase of early development, we will focus on the establishment of neural networks during development. In this section, we describe simulations of robustness against structural changes and of the spatial development of neural networks.
10.2.1 Robustness Toward Structural Damage
Compared to technical networks (power grids or communication networks), the brain is remarkably robust toward damage. On the local level, Parkinson's disease in humans only becomes apparent after more than half of the cells in the responsible brain region have been eliminated . On the global level, the loss of the whole primary visual cortex (areas 17, 18, and 19) in kittens can be compensated by another region, the posteromedial suprasylvian area (PMLS) . On the other hand, the removal of a small number of nodes or edges of the network can lead to a breakdown of functional processing. As functional deficits are not related to the number or size ...