Differential regional brain growth and rotation of the prenatal human tentorium cerebelli

Abstract

Folds of dura mater, the falx cerebri and tentorium cerebelli, traverse the vertebrate endocranial cavity and compartmentalize the brain. Previous studies suggest that the tentorial fold has adopted an increasingly important role in supporting the increased load of the cerebrum during human evolution, brought about by encephalization and an adaptation to bipedal posture. Ontogenetic studies of the fetal tentorium suggest that its midline profile rotates inferoposteriorly towards the foramen magnum in response to disproportionate growth of the cerebrum.This study tests the hypothesis that differential growth of the cerebral and cerebellar components of the brain underlies the inferoposterior rotation of the tentorium cerebelli during human fetal development. Brain volumes and tentorial angles were taken from high-resolution magnetic resonance images of 46 human fetuses ranging from 10 to 29 gestational weeks. Apart from the expected increases of both supratentorial and infratentorial brain volumes with age, the results confirm previous studies showing a significant relative enlargement of the supratentorial volume. Correlated with this enlargement was a rotation of the midline section of the tentorium towards the posterior cranial base. These findings support the concept that increases of supratentorial volume relative to infratentorial volume affect an inferoposterior rotation of the human fetal tentorium cerebelli. These results are discussed in the context of the role played by the tentorium cerebelli during human evolution and underline implications for phylogenetic and ontogenetic models of encephalization.

Mosaic Evolution of the Basicranium in Homo and its Relation to Modular Development

“…Analysis of shape changes during fetal ontogeny has shown flexion followed by retro-flexion of the cranial base between 10 and 29 gestational weeks and coronal petrosal re-orientation associated with an increase of supratentorial brain volume (Jeffery 2002a;Jeffery and Spoor 2002). Lateral ontogenetic shape changes of the developing prenatal basicranium are relatively unknown and documented mainly (although not exclusively) on a descriptive morphological basis (O'Rahilly and Gardner 1972;BachPetersen and Kjaer 1993;Bach-Petersen et al 1994;BachPetersen et al 1995;Nemzek et al 2000).…”

“…Main stream ideas in paleoanthropology assert a strong correlation between encephalisation and cranial base flexion across ontogeny and phylogeny (Biegert 1957;Gould 1977;Ross and Ravosa 1993;Ross and Henneberg 1995;Spoor 1997;Lieberman et al 2000;Ross et al 2004), despite the fact that purely mechanistic principles assessed on the basis of prenatal data do not explain the underlying causal principles (Jeffery 2002a;Jeffery and Spoor 2002).…”

Brain expansion and comparative prenatal ontogeny of the non-hominoid primate cranial base

“…Greater increases of the supratentorial portion of the human fetal brain, which contains the cerebrum, compared to the infratentorial portion, consisting of the cerebellum and brainstem, have been documented Larroche, 1990, 1992;Jeffery, 2002a). Moreover, Moss et al (1956) had previously suggested that such differential encephalization shapes brain topography and leads to ontogenetic changes in posterior cranial fossa morphology.…”

The pattern of endocranial ontogenetic shape changes in humans

“…1995; Jeffery & Spoor, 2002). Jeffery (2002) showed that in human fetuses the supratentorial brain (the cerebrum located superior to the tentorium cerebelli ) increases in size relatively more than the infratentorial brain and that this is correlated with inferoposterior rotation of the tentorium cerebelli . Postnatally, the cranial base flexes again until about 2 years of age and thereafter the angle is relatively stable (Lieberman & McCarthy, 1999), while brain size further increases.…”