This depressing model posits inexorable, unflinching and deleterious behavioral effects due to the absence of nerves in aging people. This destruction is selective, with different areas undergoing specific types of damage, a fact that can be empirically observed. A summary of a few affected areas of destruction is provided in the illustration. The Second Model Advocates of the Neuronal Plasticity Model have one word for those in the Fallout camp. The heart of this alternate hypothesis has to do with the fact that neural pathways within the brain are not nearly so set in stone as once believed.
Neurons exist that grow new axons or longer dendrites when neighboring neurons are damaged.
As mentioned above, there is evidence to suggest that neurons can grow clear into adulthood. Even non-regenerating neurons may have the ability to change their synaptic associations with other healthy nerves. The biology of learning may involve actual physical synaptic changes in the associations between existing neurons. These data do not point to some brain that slowly sets up like poured concrete, but to a living organ fully interactive with its environment. These ideas can affect deeply how the aging human brain is viewed.