Quantitative Studies Defining the Cellular Composition of the Human Brain and Spinal Cord

Abstract

In 2009, a study using a new method, called the isotropic fractionator, challenged the long-standing “common” knowledge about the cellular composition of the human brain, by claiming a much lower glia neuron ratio. This study also asserted that glia numbered less than 80 billion, a drastic reduction from the several trillion glia cells previously presumed to be present in human brains. To assess the validity of these claims, I first tested in a series of calibration and validation experiments whether the isotropic fractionator (“brain soup” method) yielded data equivalent to the conventional, and already validated, histology/stereology methods. When I found that differences between the new and the older methods did not account for the discrepancies between conclusions, I then contributed to a systematic review of the literature to determine the source(s) of the incorrect information that had permeated all major textbooks and had been considered to be “common knowledge.” This work corrected 50 years of misinformation about the cellular composition of the human brain. Having clarified the cellular composition of the human brain, I then examined, for the first time quantitatively, the cellular composition of the human spinal cord and compared it with that of other vertebrate species to identify evolutionary trends.