Three-dimensional cytoarchitectonic analysis of the posterior bank of the human precentral sulcus

Abstract

Studies employing functional magnetic resonance imaging have identified the human frontal eye field as being in the anterior and partly in the posterior wall, as well as at the base of the precentral sulcus. Moreover, it is known that the frontal eye field extends rostrally to the superior frontal sulcus. According to Brodmann's cytoarchitectonic map, this region belongs to the dysgranular Brodmann area 6 of the premotor cortex. However, the frontal eye field in non-human primates has been located within the arcuate sulcus in Brodmann area 8, generating considerable debate about where to locate exactly the frontal eye field in humans. Functional studies of the primate frontal eye field have revealed a principal homology of voluntary saccadic control systems in human and old-world monkeys, especially the macaque. But these homologies seem to be contradicted by the reported topographic localization at the cytoarchitectonic level. Therefore, we studied the cytoarchitectonic structure of the posterior bank of the precentral sulcus of a human brain, employing newly developed spatial mapping techniques to provide data about whether or not this region should be considered cytoarchitecturally homogeneous or heterogeneous. We used functional magnetic resonance imaging results, as an initial guide in localizing a region which is activated by saccadic tasks. A maximum of activation was detected around the junction of the superior frontal sulcus and the precentral sulcus extending 1.5 cm along the precentral sulcus in direction of the lateral sulcus. Here, one human brain has been analyzed to obtain preliminary data about the cytoarchitectonical changes of a part of area 6. Statistical analysis of the three-dimensional architectonic data from this region allowed us to identify a zone at the posterior bank, which in other studies has been associated with a functional region that controls pursuit eye movements and performs sensory-to-motor transformations. We found two significant sectors along the ventral part of the posterior bank of the precentral sulcus. The caudal transition region coincides partly with a region that integrates retinal and eye position signals for target location, arm, and axial movements. The second more ventrally located region is attributed to process oral-facial movements. The caudal transition region coincides with our functional magnetic resonance imaging investigation. It was revealed that this region lies at the inferior frontal eye field, where a pronounced activation over a larger region can be stimulated. Currently, more studies are needed to combine functional magnetic resonance imaging data of maximal activation with data from whole histologic brain sections of more individuals and to quantify the variability of this region and its sub-regions by means of a standardized brain atlas.