Cell counting in the human brain: traditional and electronic methods.

Whether or not a proportion of nerve cells disappears from the human brain during adult life remains a controversial question 80 years after it was first asked. In this paper the authors review briefly the reasons for this uncertainty and describe an attempt to find an answer in so far as the cerebellar Purkinje cells are concerned. A loss of about 2-5 % per decade was identified. The problems raised by cell counting in the cerebral cortex are outlined and a new method is described which may prove suitable for neuronal counting in these regions using an image analysing system.