Precuneus and chimps

Bruner et al 2016 - Brain Structure and FunctionWe modern humans have larger parietal bones and large parietal lobes when compared with extinct human species and living apes. We also have an ontogenetic parietal bulging stage, a stage which is absent in apes and Neandertals. Interestingly, a main factor of variability in our brain morphology is the size of the precuneus, in terms of proportions and cortical surface area. Now we have compared human and chimp brains, and here it goes again: the main difference is a much larger precuneus in our species. It doesn’t look like an allometric issue, being possibly associated with that bulging stage specific of modern humans, and even absent in large-brained Neandertals. The precuneus is essential in visuospatial integration, coordinating brain, body, and environment, and bridging the somatosensorial experience with simulation and self-awareness. It is a key element to integrate space, time, and  social perception. It is also worth noting that parietal lobes are particularly vascularized in our species, and the precuneus is a high-metabolic and heat-accumulating element. This may be interesting when considering that it suffers early metabolic impairments in Alzheimer’s disease, a pathology particularly associated with our species. The precuneus is also a central hub of the default mode network. Interestingly, at least in adult modern humans the size of the parietal lobes is inversely correlated with the size of the frontal and temporal lobes, introducing some phylogenetic issues on the evolution of the fronto-parietal system.

For a long time we have been looking for subtle differences between human and ape brain. This one looks not that subtle. Any functional or histological change behind this expansion, at inter-specific and intra-specific level, is still to be investigated. But most of all, it remains to be established the nature of such morphological variations. Genetic factors and selective processes cannot be excluded, but these areas are also particularly sensitive to environmental influences, including training and cultural effects.


2 Responses to “Precuneus and chimps”

  1. 1 Evie January 15, 2016 at 23:04

    I’m strongly interested in paleoneurology and, as a student, am wondering what I could do which would help in pursuing this as a career?

  2. 2 emilianobruner January 16, 2016 at 11:31

    Well, in terms of academic career, biology is probably the most direct road. Paleoneurology deals with anatomy, morphology, skulls and brains, integrating all this with information from neuroscience and paleontology. So biology looks the best background needed to begin with.

    However, paleoneurology in the strictest sense may be too “narrow” as discipline, because if one limits the study to fossils and endocasts the information is probably not that much to allow the development of complete and self-sustainable research lines. In my view, paleoneurology is a relevant component of a wider field: evolutionary neuroanatomy.

    For example, we have to take seriously into account that most traits and characters investigated in paleoneurology are not really known even for modern species. We cannot study on few fragmented fossils some complex and complicated features and processes that are not even known for billions of living people!

    Furthermore, the small sample sizes available in paleontology are almost never sufficient to test in quantitative terms a scientific hypothesis. So in general we have to use information form living species to develop a proper theoretical and quantitative framework, and then tests fossils within this framework, as “special case-studies”. Working only with fossils can just give descriptive results, and this can be interesting and important, but not sufficient in science.

    That’s why paleoneurology must be interpreted as a complementary part of something definitely more comprehensive.

    You probably know Springer has recently published this book:

    The University of Colorado has a Center for Cognitive Archaeology with on-line courses, including paleoneurology:

    Thanks for your interest, Evie, and do not hesitate to ask more!

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