The evolution of the meningeal vascular system in the human genus: from brain shape to thermoregulation

Abstract

Objectives: The imprints of the middle meningeal vessels make it possible to analyze vascularization in fossil specimens. The association between changes in the cortical anatomy and vascular organization raises questions about the actual physiological meaning of these features, most of all when dealing with the origin of the modern human brain. Metabolism and thermoregulation may be relevant factors in influencing morphological adaptations between brain and vessels. This study is aimed at investigating the relationships between endocranial morphology and endocranial vessels in modern humans and to analyze the pattern of heat dissipation through the endocranial surface in fossil specimens. Methods: Through angiotomography, it is possible to make an anatomical reconstruction of the meningeal and cerebral vessels, providing information on the morphology of the endocranial vascular system. At the same time, digital modeling can be performed to investigate the relationships between the endocranial geometry and physical properties such as heat dissipation patterns in extinct hominids. Results: The middle meningeal network is largely independent from the cerebral vascular system. Furthermore, in adults, the medium and upper tracts of the middle meningeal artery shows scarce or absent blood flow. Parietal bossing in modern humans involves relative cooling of the cortical surface at the supramarginal gyrus. Conclusions: The evidence does not support a thermoregulatory role for the meningeal vascular network, at least in adult normal blood flow conditions. On the other hand, biomechanical protective functions (hydraulic skeleton for shock adsorption) cannot be ruled out.