Role of Mechanical Factors in the Morphology of the Primate Cerebral Cortex

The convoluted cortex of primates is instantly recognizable in its principal morphologic features, yet puzzling in its complex finer structure. Various hypotheses have been proposed about the mechanisms of its formation. Based on the analysis of databases of quantitative architectonic and connection data for primate prefrontal cortices, we offer support for the hypothesis that tension exerted by corticocortical connections is a significant factor in shaping the cerebral cortical landscape. Moreover, forces generated by cortical folding influence laminar morphology, and appear to have a previously unsuspected impact on cellular migration during cortical development. The evidence for a significant role of mechanical factors in cortical morphology opens the possibility of constructing computational models of cortical develoment based on physical principles. Such models are particularly relevant for understanding the relationship of cortical morphology to the connectivity of normal brains, and structurally altered brains in diseases of developmental origin, such as schizophrenia and autism.Synopsis: How are the characteristic folds of primate brains formed? New answers to this old question support the idea that folding occurs as nerve fibers connect the brain's different surface regions. The fibers pull together regions that are strongly connected, while unconnected regions drift apart. Furthermore, as the brain develops before birth and its surface expands, folding may affect the passage of new neurons into different regions, influencing the brain's architecture. These findings underscore the role of mechanical forces in shaping the normal brain. Moreover, the findings suggest that changes in brain shape in developmental diseases, such as schizophrenia and autism, may result from changes in the connections.