John R. Wherrett, MD, PhD, FRCPC, Department of Medicine (Neurology), Toronto Western Hospital and University of Toronto, Toronto, ON.

Contemporary technologies, including digital imaging of the brain during life and quantative microscopy (unbiased stereology) for estimating histological features postmortem, have resulted in important new knowledge about changes in the brain that accompany healthy aging, including evidence that grey matter atrophies with an anterior-posterior gradient. Neurons shrink but numbers are preserved; however, there is moderate reduction in dendritic spines and in synapses that have altered function. This is to be interpreted in the light of evidence for neurogenesis continuing into late life. White matter volume increases into maturity, but in aging there is a marked reduction due mostly to a loss of small myelinated fibres. Cell inclusions characteristic of neurodegenerative disease are commonly found postmortem in the healthy aged.
Key words: brain, aging, morphometry, imaging.