Morphological Differences in the Parietal Lobes within the Human Genus A Neurofunctional Perspective

There have been very few morphological studies regarding brain parietal volumes. This is probably a result of the fact that their boundaries are rather difficult to establish. Functions of the parietal lobes that have already been documented range from visuospatial integration, category recognition, and praxis to orientation, numerical processing, and speech decoding. It has been hypothesized that the parietal lobes have had a major role in the evolution of the human brain because of their morphological changes. As brain size increases, they undergo relative flattening in nonmodern humans. This pattern is stressed in Neanderthals, which show, however, a certain widening of the parietal volumes. Only Homo sapiens shows a generalized enlargement of the entire parietal surface. Comparing the modern endocranial geometry with the configuration from extinct species, it seems that the lower parietal areas are displaced inferiorly. This suggests that the upper areas, or the intraparietal sulcus, have been involved in these morphological variations. The role of the upper parietal lobule in the recognition and codification of the outer spatial environment and the associated integration between the outer frame and the inner perceptions would seem to indicate that such morphological changes may also have been related to important neurofunctional differences.