chapter  2
Fundamentals of Brain-Behavior Function and Dysfunction
Pages 28

A simplistic explanation of why the brain and other CNS tissue does not repair itself in the manner of other bodily tissue is that humans may often be better off without such recovery. As curious as it may seem, a major part of brain development involves neuronal pruning, or modification and death of neurons. Neuronal pruning serves to eliminate inappropriate neural connections and maximize correct connections (Holmes, 1993). Between birth and late adolescence we lose about 7 billion neurons, apparently as part of an elegant design to enhance our ability to think accurately and quickly. The process of thinking involves a complex mosaic of neuronal links that would be severely disrupted if programmed neurons were replaced with new or unprogrammed neurons when they died. Confusion stemming from widespread regeneration of neuronal tissue might make us as helpless as babies, leaving us unable to experience the world in any coherent fashion. Instead, the brain is often highly adept at preserving its functional integrity despite damage. It is thought that information is rerouted through different channels after brain injury. These compensatory mechanisms often successfully provide for a systemic adaptation despite injury. However, it is unknown how the brain is able to accomplish this feat.