Efforts to parcellate the cortex into areas based on fine-scale anatomical signatures (e.g., cytoarchitectonics) date back to the early years of the last century. In the ensuing decades, rapidly growing knowledge of cortical connections encouraged neurobiologists to search for connectivity-based principles underlying the organization of the cerebral cortex. Using such an approach, Felleman and Van Essen presented, in their 1991 paper, a connectivity-based hierarchical principle dictating the relationship between cortical areas. This helped invigorate debates on the principles underlying cortical organization, including searches for alternative, or complementary, principles.
