Effects of an enriched environment on myelin sheaths in the white matter of rats during normal aging: A stereological study

► Rats were reared in either an enriched environment or a standard environment for 4 months. ► Myelin sheaths were quantitatively investigated using stereological methods. ► Enrichment increased the myelinated fiber length of aged white matter. ► Enrichment increased the axon volume and myelin sheath volume of aged white matter. ► Enrichment mostly increased smaller fibers with thinner myelin sheaths.