Stereological quantitation of human brains from normal and schizophrenic individuals

The complex organization and high density of nerve cells in the human brain presents a challenge to the estimation of total cell numbers. The first unbiased counting method, the disector, was described in 1984 and has since made it possible to accurately count total neuron numbers in any region that can be defined, while excluding artifacts of earlier counting methods. The disector method has been applied to normal neocortex and to four subcortical brain regions from schizophrenics and controls. The total neuron number in neocortex in 26 normal individuals was estimated to be 25·109. A 40 and 50% reduction of total nerve cell number was found in the mediodorsal thalamic nucleus and nucleus accumbens in schizophrenics, respectively. Furthermore, the Cavalieri principle has been used to estimate the volume of human cortex, white matter, central grey regions and the volume of the ventricular system in both controls and schizophrenics. As shown by these studies, the introduction of unbiased stereological methods and subsequent modifications in recent years have made it possible to estimate a number of parameters in the human brain without the biases included in most classical works. By comparison, earlier conventional counting methods have been relatively time consuming, mostly biased to a smaller or larger degree, and generally less precise. The application of these new neurostereological methods will undoubtedly provide greater confidence for future brain studies.