What capacity does the brain have to repair itself after injury or disease?

It has long been accepted dogma that central nervous system doesn't regenerate itself after traumatic injury or widespread cell death. This is supported by a fact that people with severe head or spinal cord trauma are commonly not able to recover their pre-injury level of function. Though, recent discoveries - including the revelations that adult brains can form new nerve cells and immature neural stem cells can migrate to injured areas of animals' brains - have forced a reconsideration of this accepted principle. Additionally, improved understanding of how nerve cell connections are formed in early brain development has fuelled hope that these developmental processes might be recapitulated to repair damaged nervous system.