Brain and braincase

Bruner et al  - JAnat 2015Parietal lobes are a main source of morphological variation within humans and within hominids. This month we have published a study on the relationships between bones and lobes, to evaluate how and how much such variation in the cerebral areas can influence the variation of the corresponding cranial points. There is a size correlation  between parietal bones and parietal lobes, but it is small. There is a lot of individual variation, most of all in the precuneus. Changes of the brain proportions do not seem to influence the spatial relationships of the bones. Therefore, when the boundaries of the parietal lobes change, the boundaries of the parietal bone do not. It is like the brain “slides” under the bones, without strict constraints due for example to the connective meningeal interface. So, the larger the parietal lobe, the more it approaches the frontal bone. Such lack of marked correspondence between bones and lobes suggest cautions when using cranial landmarks to estimate brain boundaries, like in neurosurgery or in paleoneurology. Now, two hypotheses can be put forward, taking into consideration that the growth of the parietal area in our species is characterized by a very early post-natal stage. First hypothesis: such lack of correspondence can be present since the beginning, and hence that early parietal bulging will separate the limits of the parietal lobe and bone. Second hypothesis: during that early stage parietal lobe and bone grow together (the latter in response to the former), but later stages of spatial changes in the anterior districts (frontal bone and lobe) alter their original correspondence. This study deals with modern humans, and it will be interesting to consider the same spatial relationships in other primates. Nonetheless, at least for Homo sapiens, we can say that between parietal lobes and parietal bones there is a good geometrical correspondence (overall curvature), a modest size correlation (length), and a variable spatial relationship (boundaries).

Victoriapithecus

Victoriapithecus (Gonzales et al 2015)Macaques and chimps are still used in anthropology and neuroscience as “primitive models” for human evolution. This is of course a non-sense: all living species, after the divergence from a common ancestor with modern humans, have evolved and changed as humans did. The genus Macaca is as young as the genus Homo, and living macaques and living humans are recent species in evolutionary terms, approximately with a comparable age. The problem with chimps is that we miss fossils, so we ignore how and how much their lineages has changed. But we have more information on macaques, and in general on fossil cercopithecoids. A very detailed and informative study on the endocast of Victoriapithecus has been recently published, definitely a  stimulating and comprehensive article for primate paleoneurology. This Old World monkey, dated to 15 Ma, had a small cranial capacity and large olfactory bulbs, but a sulcal pattern similar to modern cercopithecids. This suggests two major points. First, in Old World monkeys sulcal complexity evolved before brain size increase. Second, brain morphology evolved in cercopithecoids and hominoids through distinct processes, mixing primitive traits, different mechanisms, specific adaptations, and some convergences. These results stress further the necessity of caution and of a proper evolutionary perspective when dealing with comparative primatology and human brain evolution: macaques (and chimps) are derived species as we are, with their own independent evolutionary histories. They can provide information on biological factors which are shared among our respective lineages, but it would be an error to think that their anatomy, physiology, or genetics, represent an ancestral condition.

Social brain

Lucy to LanguageI think Herbert Spencer was totally right stressing that humans are the ultimate problem of biology and the initial factor of sociology. Robin Dunbar’s Social Brain Hypothesis integrates information from many different fields to provide a comprehensive perspective on human brain evolution and its associated social context. Like gas molecules, it looks like individuals are not predictable in terms of behaviour but groups, indeed, are. The larger the group, the more the social responses and dynamics can be predicted by apparently simple rules, often based onto our primatological nature. Our brain biology supplies opportunities and constraints to our social networks. This book “Lucy to Language: the Benchmark Papers“, puts together about twenty review articles published in the last decade on the social brain hypothesis. This topic is definitely relevant and promising for every approach in evolutionary anthropology. This month I have published a review on this book, introducing issues in paleoneurology and cognitive archaeology which can be important to integrate these perspectives with evidence from the fossil record.

Visuospatial evolution

Descartes - Meditations metaphysiques 1641Visuospatial integration is essential in handling, tooling, simulation, and many specific tasks which are supposed to be crucial for human evolution. However, it may be even more important for theories on extended cognition, taking into account the relevance in coordinating the relationships among brain, body, and environment. This is something directly associated with concepts like embodiment, material engagement, and brain-artefact interface. And this is pretty intriguing when considering that the upper and medial parietal areas, which are major functional nodes of visuospatial integration, show a remarkable enlargement only in Homo sapiens. Together with Atsushi Iriki (Riken Brain Institute), we have now published a review trying to interlace all these issues: Extending mind, visuospatial integration, and the evolution of the parietal lobes in the human genus. We have tried to integrate topics in neurobiology, paleoneurology, cognitive archaeology, and comparative primatology, to understand why and how visuospatial integration may have been important, in our genus and in our species, for enhancing material engagement and embodying capacities. This article will be part of an issue of Quaternary International dedicated to the importance of “Material dimensions of cognition”. At the same time, the Journal of Anthropological Sciences is now publishing a second forum on the “three hands” of the Neandertals. The hypothesis of a mismatch between visuospatial functions and cultural complexity in this human species is further discussed with comments by Leee Overmann, Enza Spinapolice, Joseba Rios Garaizar, Ariane Burke, Carlos Lorenzo, and Duilio Garofoli. All the papers of the forum are free to download.

Prize!

Journal of Anatomy Bruner et al 2014

Journal of Anatomy Best Paper Prize 2014”  to Bruner E., Rangel de Lázaro G., de la Cuétara JM., Martín-Loeches M., Colom R. & Jacobs HIL. 2014. ‘Midsagittal brain variation and MRI shape analysis of the precuneus in adult individuals’,  Journal of Anatomy, Volume 224, Issue 4, April 2014, pp 367-376,  as the most outstanding article published during 2014! The prize is awarded by the Anatomical Society. Thanks!!!

Continuity

Humanchimp_2015Since the earliest hypotheses on human evolution there is major issue on continuity vs discontinuity. Charles Darwin suggested that only a matter of degree separates human and non-human species, also in the cognitive sense. From the opposite side, many biologists (mostly those involved in molecular sciences) are constantly looking for unique features, single changes that can switch the light on. The fact that there is still no agreement or evidence giving definitive support to any of the two perspectives may suggest that the debate is simply oriented toward an unfruitful direction. If there is still no good answer, maybe it is because there is a bad question. Is a faster car faster just because it supports higher speed or because it is differently designed? Both. What about evolutionary “shifts” based on the same processes? Are they a continuous or a discontinuous phenomenon? Both. Brain evolution is particularly sensitive to the continuity vs discontinuity debate. Is there a real biological frontier between continuity and discontinuity? It looks like a fractal loop and any change is, after all, a discontinuity in something. In paleontology, continuity is often a matter of appearance concerning the homogeneity of the fossil record, which gives a partial and largely incomplete view of the variation. Paleontology is furthermore based on a specific biological component – morphology – which may not necessarily have a linear correspondence with the underlying evolutionary processes. What if continuity and discontinuity are just in our head, in our eyes, in the form we perceive reality, in the form we analyze reality? We need fixed categories to decompose the scene and then recompose it by searching for relationships. Maybe this necessity is a limit, or maybe it is an advantage. But we think through categories. Evolution does not.

Warping brains

Ogihara et al 2015The team coordinated by Naomichi Ogihara has published an analytical review on computed reconstruction of fossil crania and interpolation of their brain morphology. The article presents and discusses the applications of biomedical imaging in paleontology, including technical and algebraic details. Automated assembling of fossil fragments is approached following geometric similarity, fracture surfaces, pattern matching, smoothness, and anatomical correspondence. Skulls, endocasts, and brains are integrated mixing information from computed tomography and magnetic resonance, and spatial deformation functions are used to interpolate brain morphology in fossil species. This is a very useful paper both for the technical issues and for general perspectives in digital anatomy and computed morphometrics in paleoneurology. Additional information on this topic can be found in the paper by Gunz and colleagues on virtual reconstruction and in the review by our team on functional craniology.


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