AGE-INDUCED WHITE-MATTER CHANGES IN THE HUMAN BRAIN - A STEREOLOGICALINVESTIGATION

In the present pilot study, age-related white matter changes were inve stigated by the use of design-based stereological methods. In the brai ns of elderly subjects, the total volume of the white matter and the t otal volume of the myelinated fibers therein were lower than in those of young subjects (15% and 17%, respectively), but the differences wer e not statistically significant. The rotal length of the myelinated fi bers of the white matter in the elderly group of 86,000 km was, statis tically, significantly decreased by 27% compared with 118,000 km in th e young group. This loss of the total nerve fiber length was accompani ed in particular by a decline of the myelinated fibers with a small di ameter. The mean diameter of the myelinated fibers in the young group was significantly smaller than in the old group, but the relative size distributions of the myelinated fiber diameters between the young and old groups were similar. Our findings show that the atrophy of the hu man white matter during ageing is probably caused by a loss of myelina ted fibers with a small diameter. (C) 1997 Elsevier Science Inc.