Quantitative Studies Defining the Cellular Composition of the Human Brain and Spinal Cord
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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 thenewandtheoldermethodsdidnotaccountforthediscrepanciesbetweenconclusions, Ithencontributedtoasystematicreviewoftheliteraturetodeterminethesource(s)ofthe 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 cellularcompositionofthehumanbrain.Havingclarifiedthecellular composition ofthehumanbrain, 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.