The cytoarchitectonic map of korbinian brodmann: Arealisation and circuit specialisation

Abstract

Korbinian Brodmann is best known for his 1909 monograph on comparative localisation of cerebral cortex in a variety of mammals, including man. His areas are still widely used to delineate cortical functional regions. He identified homologous parts of the cortex in different animals by their structure and produced an organic theory of cortex based on anatomical features. He formalised the description of the cortical pattern as being composed of six basic layers, with variations between animals and between areas. He integrated phylogenesis and ontogenesis with observations of adult cortical structure, function and pathology. Later, Brodmann turned to a systematic study of human brains of different races, culminating to a paper on anthropological aspects of cortical anatomy in 1913. His work over his short lifetime is a rich source of quantitative information and is of importance for the interpretation of modern imaging studies, particularly involving visual or prefrontal cortex, and the search for a neuroanatomical basis for human consciousness and intelligence. With the advent of new methodologies it has been possible to probe neuron structure at the microscopic level in Brodmann's cortical areas, teasing out and quantifying elements of circuit structure and specialisation. The study of pyramidal cells, the most abundant neuronal type in cortex, has revealed significant and systematic differences in structure and integrative ability among cortical areas, which reflect the physiological characteristics of the neurons and functional complexity. Moreover, comparison of pyramidal cell structure in homologous cortical areas among species reveals different trends among different cortical areas. Pyramidal cell structure in Brodmann's area 17, for example, varies relatively little among primate species whereas pyramidal cells in granular prefrontal cortex are larger, more branched and more spinous in progressively larger prefrontal cortices. Pyramidal cells in prefrontal cortex in man, that region associated with higher cognitive functions, are more complex and integrate more inputs than lower order primates, bridging Brodmann's theories in prefrontal cortex and Cajal's theories on the psychic cell in present day thinking on intelligence.