Posts Tagged 'Homo sapiens'

Jebel Irhoud

New fossils and age for Jebel Irhoud. Jean-Jacques Hublin and colleagues have published new specimens, new analyses, and a new chronology pointing at 300 ka. All their results robustly confirm what we already knew on these populations: modern face, primitive braincase. Two major advances of these new findings are i) the morphology of Irhoud 10 (the new skull) is apparently so similar to Irhoud 1 (the old skull found back in the ’60s), suggesting that such phenoptype was common and representative, and not only the result of individual variation, and ii) the age around 300 ka, that suggests an earlier origin for our lineage. The braincase and endocast of the new skull were not analyzed in this study, probably because of some deformation, and there are no photographs of the fossils (in the paper we can only see the virtual reconstruction of the face), so an assessment of its paleoneurological traits is not available yet. But in this article they re-analyze the old specimens (Jebel Irhoud 1 and 2) through shape analysis, confirming a plesiomorph braincase, apparently (Extended Data Figure 4) because of a reduced parietal and frontal size and curvature. Here a 2013 study I coauthored with Osbjorn Pearson on Jebel Irhoud’s endocast, supporting the same conclusion: they were probably modern humans, but without modern brains. If they were our ancestors, something triggered a subsequent change in brain proportions and organization.

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Precuneus

Bruner et al JA2014Paleoneurological studies based on endocranial geometry suggested that a spatial dilation of the deep parietal areas was the major morphological difference between modern and non modern human brains. In our species, the morphogenetic change associated with this parietal bulging was then localized in a very early post-natal period, in a  stage which is absent in chimpanzees or in Neandertals. In the meanwhile the deep parietal areas were demonstrated to have also special cytoarchitectonic elements in modern humans, to be the main functional and structural node of the human brain organization, to be critically involved in major cognitive capacities through the fronto-parietal connections, to be central to the default mode network, and to be essential in human-specific cognitive processes involving imagination and simulation. Such specific parietal modifications have been also tentatively associated with species-specific vulnerability to neurodegeneration in our species. Actually, the early stages of Alzheimer’s disease are associated with metabolic, functional and structural impairments at the deep parietal areas, like the precuneus. These brain districts have been scarcely studied in term of morphology because of their difficult position, multifunctional roles, and blurred anatomical boundaries. Through a MRI shape analysis of adult human brains we have now identified the main character associated with individual brain variation in our species: the geometry of the precuneus. With a negligible effect of brain size or sex, the proportions of the precuneus are the main determinant of the midsagittal brain geometry. The brain morphological variation of the human genus and the brain morphological variation among adult modern humans share the same pattern: parietal bulging. And, at least for modern humans, this pattern is strictly determined by one single character: the longitudinal extension of the precuneal area. Evolutionary and functional evidence both converge toward the neural element which is at the same time the most variable at intra-specific level, strongly influencing our brain form. Many coincidences, which may be the result of the delicate spatial position of the deep parietal areas in the overall brain geometry. Or may there be more than this?


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  • Fall 2017 CCA Course Offerings
    The Center for Cognitive Archaeology is offering three exciting classes this semester: Neurocognition of Art, Cognitive Evolution, and Neandertal Cognition. Follow the link below for detailed information. https://www.uccs.edu/~cca/

RSS The Skull Box

  • Eye-brain spatial relationship
    We have just published a new study on the spatial relationship between visual and endocranial structures in adult modern humans, chimpanzees, and fossil humans. The survey was conducted in collaboration with Michael Masters from Montana Tech (USA), who previously hypothesized that, in modern humans, the positioning of the orbits below the frontal lobes coupl […]

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RSS Neurophilosophy

  • Researchers develop non-invasive deep brain stimulation method
    Researchers at MIT have developed a new method of electrically stimulating deep brain tissues without opening the skullSince 1997, more than 100,000 Parkinson’s Disease patients have been treated with deep brain stimulation (DBS), a surgical technique that involves the implantation of ultra-thin wire electrodes. The implanted device, sometimes referred to as […]

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