Anatomical Parcellations of Brodmann's Areas 4 and 6: A Study on Cortical Thickness for Improved Neurosurgical Planning

The cerebral cortex, comprising six layers known as the neocortex, is a sheet of neural tissue that contains regions for neurosurgical planning, including the primary motor cortex (PMC), the supplementary motor cortex (SMA), and the primary somatosensory cortex (PSC). However, knowledge gaps persist concerning the transition points between areas 3 to 4 and 4 to 6 and the SMA's extent. This study aims to develop a non-invasive protocol using T1/T2 weighted imaging to identify crucial anatomic borders around the primary and supplementary motor cortex for neurosurgical planning. A comprehensive literature search on the cytoarchitectonic borders of Brodmann's areas 3a, 4, and 6 was conducted, and relevant articles were selected based on their examination of these borders. The primary motor cortex was found to be the thickest region in the human brain, with discernible differences in thickness between areas 4 and 6. T2-weighted images revealed significant cortical thickness differences between the precentral and postcentral gyrus. Various methods have been employed to parcellate borders between cortical regions, including Laplace's equation and equi-volume models. A triple-layer appearance in the primary motor cortex and a novel method based on myelin content demonstrated consistent agreements with historically defined cytoarchitectonic borders. However, differentiating areas 4 and 6 from MR imaging remains challenging. Recent studies suggest potential methods for pre-surgically identifying the primary motor cortex and examining differences in cortical thickness in diseases. A protocol should be established to guide neurosurgeons in accurately identifying areas 4 and 6, possibly using imaging modalities superimposed on myelin maps for differentiation and determining area 6's anterior extent.