Bok’s equi-volume principle: Translation, historical context, and a modern perspective

Abstract

The human brain has a complex and unique structure, characterized by intricate three-dimensional folds. These folds, and the mechanisms for their formation, have been studied for over a hundred years. Here we offer a full translation of the pivotal (1929) work by Siegfried Bok, “Der Einflußder in den Furchen und Windungen auftretenden Krümmungen der Großhirnrinde auf die Rindenarchitektur” (“The Influence of the Curvature Occurring in the Folds and Turns of the Cerebral Cortex on Cortical Architecture”). This paper established the influential equi-volume principle, which stated that cortical and laminar thicknesses, along with neuronal shape and fiber orientation, change in order to preserve relative volume throughout the folds of the cortex. We also offer a commentary on the main points of the work, looking at Bok’s observations and predictions regarding the structure of neurons, cortical laminae, and the cortex itself, throughout the folds and curves of the brain. His equi-volume principle has held up to decades of experimentation and, even today, has important implications for the analysis of brain structure and function.Statement of Significance: This manuscript presents, for the first time, a full English translation of the foundational neuroanatomy article, “Der Einflußder in den Furchen und Windungen auftretenden Krümmungen der Großhirnrinde auf die Rindenarchitektur” (“The Influence of the Curvature Occurring in the Folds and Turns of the Cerebral Cortex on Cortical Architecture”), written over 90 years ago by Siegfried T. Bok and heavily cited since then. In addition, we provide an assessment of Bok’s main points, in light of his contemporaries in research at the time, as well as more recent work during the intervening decades.