Unfortunately, age does lead to brain changes. Many older brains have changes that resemble those seen in Alzheimer's disease but do not show the full picture of the disorder. It can be debated whether this is simply very early disease that will eventually show up in the clinic, but even in the presence of these changes, the neuronal numbers are not reduced. It seems that nerve cells do not die with age. What seems most likely is that their networks become less efficient.... A typical neuron has one large fibre called the axon and a number of smaller branches called dendrites, which further branch and subbranch into a dendritic tree. These dendrites link the neuron to other neurons, forming a vastly complex network. The dendrites carry small protrusions like mushroom heads that are smaller than a micrometre and can be seen only by special microscopes. All principal neurons in the brain carry these spines on their dendrites and, for some nerve cells, these can number in the tens of thousands. They form links with spines of other neurons in junctions called synapses through which information flows from one neuron to another.... It has been shown that with ageing, the dendritic spines become less dense. There are other changes as well, especially in relation to the synapses.
Sculpture of a neuron by Roxy Paine,Museum of Contemporary Art, Sydney, May 2010.
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