Figure 6.

Average spine head diameter (d) and volume is significantly increased in aging, which is attributable to a selective loss of thin spines. All statistics were performed based on one aggregate (i.e., average) measure per animal. A, Mean spine head diameter is significantly greater in aged monkeys. B, Mean spine head volume is significantly greater in aged monkeys. C, There is no age-related difference in the average spine maximum distance from the parent dendrite, a measure that approximates the length of the spine (l). D, The cumulative frequency plot of each spine head diameter from individual animals shows that for small spines (∼0.3–0.4 μm diameter) the group data are highly unified. E, Densities of subtypes of spines based on an unbiased classifier show that there is a selective loss of thin spines in aging. *p < 0.05, **p < 0.01, ***p < 0.001; n.s., no significance.