Capillaries in the cerebral cortex of six age groups, ranging between 19 and 94 years (= 34 human brains) were stereologically investigated. Capillary parameters such as diameter, volume fraction, specific surface area, mean intercapillary distances and total length per unit cortex volume in patients older than 75 years were similar to those in young ones, 19 to 44 years old. Aged subjects between 64 and 74 years revealed increased capillary diameter, volume and total length per unit cortex volume, as well as decreased specific surface area. Frequency distributions in the same age indicate a real increase of capillary diameter and volume, as also an increase of these parameters on the level of blood vessels with diamteres greater than 8 micrometer, probably arterioles. The results of this study argue against the wide-spread assumption of a decreased blood supply in the cerebral cortex during old age. On the contrary, the capillary net is able to respond to changed metabolism and blood pressure.

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The stereological investigation comprised three groups of people aged 19 to 44, 65 to 74 and 85 to 94. Perikaryal area and circumference of cortical neurons in the superior part of the cerebral precentral gyrus were determined. Opening classes of single neurons were measured with the Leitz texture analyzer to calculate size and shape. A multivariate statistical procedure allowed comparison of the neuronal parameters between all groups. The measurements yielded smaller perikarya in the oldest group as opposed to larger ones in the young subjects. No differences were seen between young subjects and the 65 to 74-year-old group, which, in contrast, revealed as only group age-dependent changes in cerebral capillaries and small blood vessels. The differences in perikaryal size indicated that senile atrophy of neurons was most apparent in the external pyramidal layer. An influence of decreased motor impulses from the periphery on the atrophic process of neurons with predominant receptor function cannot be excluded.