Figure 7.

Scatterplots with a piecewise, linear fits showing: A) the frequency of myelinated nerve fiber profiles with altered myelin sheaths (including dense sheaths, redundant sheaths, and myelin balloons), B) the frequency of myelinated nerve fiber profiles with dense myelin sheaths, and C) the frequency of myelinated nerve fiber profiles with redundant myelin sheaths in the cingulate bundle and the genu of the corpus callosum of young (<10 years), middle aged (10-20 years), and old (>20 years) rhesus monkeys. As shown in A, a significant increase in the frequency of total altered myelin sheaths is seen in middle and old age groups in both the genu (middle age, p < 0.0001; old, p < 0.005) and cingulate bundle (middle age, p < 0.005; old, p < 0.0001). Likewsie, in B, a significant increase in the frequency of dense myelin sheaths is seen in middle and old age groups in both the genu (middle age, p < 0.001; old, p < 0.0001) and cingulate bundle (middle age, p < 0.05; old, p < 0.0001). In C, a significant increase in the frequency of redundant myelin sheaths is evident in middle age monkeys in both the genu (p < 0.001) and cingulate bundle (p < 0.05). Additionally, there is a significant decrease in the frequency of redundant myelin sheaths in the genu of old aged monkeys (p < 0.005) but not in the cingulate bundle.