Anatomo-Functional Organization of the Human Posterior Parietal Cortex – ParietalMapping

The posterior parietal cortex (PPC) is a major cortical region, involved in some of our most fundamental sensorimotor and cognitive behaviors. Hundred years ago, Korbinian Brodmann was one of the first to relate this functional diversity to the structural heterogeneities of the PPC. Using cytoarchitectonic analyses he segregated this area into four main subregions: two in the superior parietal lobule (SPL; areas 5 and 7), two in the inferior parietal lobule (IPL; areas 39 and 40). However, the crudeness of this original parcellation became rapidly evident and it is now widely established that PPC is formed of a large number of functionally and cytoarchitecturally distinct regions that are strongly and reciprocally interconnected with each other and remote cerebral areas. Yet, beyond this consensus, there is still a high level of disagreement between researchers regarding the anatomo-functional organization of PPC and many important questions remain to be answered.

The lacunae of our current knowledge are especially apparent in humans. Among all the possible reasons capable of accounting for this observation, three seem especially important. (1) Major differences exist in location, size and connectivity between human and animal parietal cortices, which make inter-species generalizations uncertain. (2) The often large lesions observed in human patients make it difficult to establish fine anatomo-functional correlations. (3) Neuroimaging studies do not always allow to determine whether a responsive area is truly necessary for the expression of a considered function (i.e. whether the 'inactivation' of this area would cause behavioral deficits) and whether the observed response reflects afferent, efferent or computational processing.

It is the aim of this project to address these limitations. Our main goal is to identify the anatomo-functional organization of the PPC in human, using mainly per-operative mapping procedures. Obviously, these procedures, also, have limitations. However, within the last 100 years, they have shown an unmatched ability to reveal motor (efferent), sensory (afferent) and functional cortical maps. Recent developments have extended these abilities to the field of cortico-cortical connectivity. To avoid ambiguity, it must be clear that per-operative mapping serves exclusively clinical purposes. In operative rooms, this procedure is only used because of its dramatic ability to reduce post-operative deficits. While helping to optimize this mapping procedure, the present project will make use of the clinical observations that will be collected in order to address fundamental questions, with the informed consent of the patients.

The main objectives of this project can be summarized as follows: (1) investigate the anatomo-functional heterogeneity of the motor, sensory, functional and connectivity maps of the PPC in humans; (2) determine how these maps adapt in response to localized brain injuries affecting specific subregions of this structure.

The close integration, within a common group of researchers and neurosurgeons that have now cooperated fruitfully for almost a decade provides a unique opportunity to carry out this ambitious proposal which is expected to produce important fundamental and clinical outcomes. At a fundamental level, this project should substantially strengthen our current understanding of both the anatomic and functional organization of the parietal cortex and the nature of the adaptations that affect this organization in response to brain damages. At a clinical level, it should improve per-operative mapping procedures known to be critical for minimizing the risk of post-operative sequelae in patients with parietal tumors. Also, by improving our understanding of the clinical manifestation evoked by specific parietal lesions, the project should provide useful information for designing better rehabilitation procedures.