Cytoarchitechtonics always seemed a very dry and not very practical branch of neuroanatomy. Pioneered by such colossal figures of neuroscience as K. Brodmann, O. and C. Vogt (Germany), R. Cajal (Spain), as well as V.A. Betz, S.A. Sarkisov, I.N. Filimonov and G.I. Poliakov (Russia) was initially based on purely visual observations of subtle differences between size, shape and distribution of different neuronal types through cortical layers in different regions of the brain. The goal of their studies was understanding of the fundamental mechanisms of brain functions: memory, conciseness, reason for mental disorders, even morphological basis of talent and geniality. Based on observed differences of neuronal architecture several versions of cytoarchitectonic maps of human brain cortex were described (Brodmann, Vogt, Economo and Koskinas, Sarkisov).
By the way, it is interesting to outline that not every neuroscientist acknowledges that the founding father of cytoarchitectonic parcellation of brain cortex was Russian (or, more precisely – Ukrainian) neuroanatomist Vladimir Alexandrovich Betz (see, for example, two reviews of history of cortical parcellation by K. Amunts and K. Zilles, 2010, “Centenary of Brodmann’s map – conception and fate”, and 2015, “Architectonic Mapping of the Human Brain beyond Brodmann”, where Betz’s name was not even mentioned). Every medical student, let alone – neuroscientist, knows about V.Betz due to his discovery of gigantic pyramidal neurons in motor “center” of human cortex, correlated to and elaborated by insight into cortical function. However, and perhaps much more importantly, his work “Anatomic evidence of two brain centers” (Betz W. 1874, “Anatomischer Nachweis zweier Gehirncentra”, Centralblatt für die medizinischen Wissenschaften, 12:578-580, 595-599), first published in Russian, and later – in German, was the first microscopic analysis of shape and size of neurons, which allowed morphological subdivision of human cortex into separate centers. These “centers” were later called “areas”.
Initial cytoarchitectonic studies were very productive, because they established the fundamental approach for understanding the localization of basic functions of human cortex. Visual, auditory, motor, somato-sensory, sensory and motor speech areas, etc. were identified and localized. However, later studies that targeted more “sophisticated” functions, like memory, self-awareness, or specific skills (for example, outstanding artistic, mathematical or linguistic abilities) did not established clear-cut localization of these functions, nor did they provide the explanation of neuronal mechanisms of such functions based on microscopic organization of specific areas. To simplify the matter, the major conclusion from such studies was significant individual variability of the human brain cortex, but more specific results were either absent, or in best-case scenarios – vague and difficult to reproduce. This also included multiple and not very successful attempts (with the exception of Alzheimer’s disease) to define morphological basis of mental disorders, like schizophrenia or manic-depressive psychosis.
Development of computerized image processing technologies and their application in microscopy stimulated a new wave of cytoarchitectonic research, which had the goal to make cortical micro-anatomy more objective and more sensitive to expected correlations with functional significance of cortical areas under study. However, for the reasons behind the topic of this review, “great expectations” for the potentials of quantitative cytoarchitecture studies did not materialize quickly enough, and were superseded by immunochemistry, receptor-autoradiography and gene expression-based microscopic studies of human brain, and especially – neocortex.
However, quite recently, yet another renaissance of quantitative cytoarchitectonic studies seems to emerge due to increasing demands for precise microscopic localization of activity maps registered during functional MRI experiments. This demand increased practical significance of methods and technologies, developed a relatively long time ago, from 40 to 20 yeas in the past, but sadly underappreciated at the time of their initial publications. One of such methods was widely publicized, another is practically unknown. Due to my personal “attachment” to both of them, but for different reasons to be revealed later, I would like to concentrate on the history and analysis of these two methods. The first is called GLI (Grey Level Index), the second – MCG (Automatic Morphocorticography). <continue reading>