NEOCORTICAL NEURON NUMBER IN HUMANS - EFFECT OF SEX AND AGE

Modern stereological methods provide precise and reliable estimates of the number of neurons in specific regions of the brain. We decided to estimate the total number of neocortical neurons in the normal human brain and to analyze it with respect to the major macro- and microscop ical structural components, to study the internal relationships of the se components, and to quantitate the influence of important physiologi cal variables on brain structure. The 94 brains reported represent a c onsecutive collection of brains from the general Danish population. Th e average numbers of neocortical neurons were 19 billion in female bra ins and 23 billion in male brains, a 16% difference. In our study, whi ch covered the age range from 20 years to 90 years, approximately 10% of all neocortical neurons are lost over the life span in both sexes. Sex and age were the main determinants of the total number of neurons in the human neocortex, whereas body size, per se, had no influence on neuron number. Some of the data presented have been analyzed by using new mathematical designs. An equation predicting the total neocortica l neuron number in any individual in which sex and age are known is pr ovided. (C) 1997 Wiley-Liss, Inc.