A re-evaluation of brain volumetric data, adjusting for scaling and phylogeny, adds further evidence against the hypothesis of morphological changes in the frontal lobes for our species. Despite a century of firm claims on the patent role of the frontal lobes in our evolution, there are now many different indications suggesting that those statements were probably excessive and not well demonstrated. It seems that there is no clear specific change in the general morphology of the frontal lobes in Homo sapiens, and even the correspondence between anatomy and functions has lost strength. We must take into consideration the possibility that differences may be subtle but important. A minor shift from the general tendency may be irrelevant for the statistical thresholds but important in biological terms (for example, this can be the case for white matter proportions). There may be also changes which have not been detected yet, as well as changes that are not evident from gross morphometrics. Furthermore, even if volumetric changes in our frontal lobes are those expected for our large brain size, the increase in terms of absolute size is patent, and this may be a relevant difference anyway. Throughout this debate, it is interesting to note how the paleoneurological information is generally ignored. Despite the many inferences on the evolutionary changes in the brain human form, there is no mention of the notable advances published on the evolution of brain geometry in our species. This is even more imprudent when considering that anthropology is currently employing very complete and powerful morphometric tools, while in neuroscience most data still refers only to general size measures. However, even using just basic morphometric variables, we know that modern humans and Neandertals experienced at least a change in the proportions of the frontal areas. Excluding the fossil evidence from the debate does not seem to be a good idea, at least when dealing with evolutionary studies.
Tags: encephalization, frontal lobes, Robert Barton
Tags: Neandertals, occipital lobes, orbits, visual cortex
Paleoneurology gets new tools. By using living species, Eiluned Pearce and colleagues look for correlations between neural and non-neural anatomical elements, and then apply their results to fossils. This approach opens up an incredibly large set of new research lines. They find a correlation between orbit size and visual cortex which, after a delicate series of normalization processes, suggests that Neandertals had larger visual areas of the brain. At the expense of the parietal ones. This new information seems to provide further support for the hypothesis of relative dilation of the parietal lobes in our species. The long chain of numerical transformations the authors applied to control any possible scaling factor is really efficient and successful. Evidently it also introduces many assumptions and estimations which call for caution when dealing with strict interpretations of the final outputs. Also, we know that only in modern humans and Neandertals the prefrontal brain areas lie on the orbital roof, generating complex constraints between brain and eyes that may produce departures from the schemes of other species. Nonetheless, with these limits in mind, we must recognize that this study supplies new and fresh ideas to our field, and relevant new information on Neandertals. It is also useful in reminding us once more that different lineages may undergo different cognitive evolution, which in the case of the brain means improving or demoting different behavioural skills. This recalculation of the different cortical areas in fossil hominids also supplies new estimations of parameters associated with primates’ biology and social structure, such as the average group size.
Many people are warning against “paleo-phrenology”, but this should not be the case. This is a correlation study. A theory can explain a correlation or fail to do it, but the correlation is there, and it can reveal underlying information. Caution is recommended, but this is always recommended in science. It is strange how we are critic against a lots of details for complex models in evolution, yet we accept overly simplistic alternatives like those associating cognition with a single molecule or gene …
A comment on National Geographic.
This week we have published a review on cranial sutures, on Child’s Nervous System. The article introduces some historical issues, then presenting the relevance of the sutures in biomedicine and anthropology. Functional craniology and fractal geometry are particularly taken into account by this team, which is specifically interested in applications of morphometrics to neurosurgery and vascular topics.
Tags: brain growth, brain size, encephalization
Christoph Zollikofer and Marcia Ponce de León have published a review on human evolution and endocasts: Pandora’s Growing Box. The article provides comments on topics mostly related to brain size, brain growth, encephalization, cranial evolution, and comparative neuroscience. There are useful notes and images on the correspondence between brain and endocast.
Tags: Alzheimer, dementia, parietal lobes
Alzheimer’s disease is more and more breaking in our society, with devastating effects in the life of an increasing number of persons. Many factors underlying this neural degeneration are still unknown. We have tried to integrate biomedical and evolutionary evidence, in a recent hypothesis published in the Journal of Alzheimer’s Disease. The fossil record suggests that our species is characterized by spatial changes at deep parietal areas like the intraparietal sulcus or the precuneus. These areas are relevant for visuo-spatial integration, memory, eye-hand coordination, and inner virtual reality. Fossils also suggest that our species is characterized by an increase in the parietal vascularization, at least on the cortical surface. We know also that at least at the intraparietal sulcus we have areas which are absent in non-human primates. Alzheimer’s disease is described only in our species. One of the first pathological events in the earliest stages of Alzheimer’s disease is a metabolic impairment at the deep parietal areas. May the Alzheimer’s disease be the evolutionary downside of a highly metabolic parietal lobe? Another paper is also in press on Journal of Anthropological Science proposing a further evolutionary framework for Alzheimer’s disease, and interpreting the neurodegenerative process in terms of human evolution, heterochrony, and energy budgets. An evolutionary point of view cannot heal or treat directly an injured brain. Nonetheless, it may give a different perspective opening to alternative strategies by looking at the pathology not only from its present, but also from its past.
Tags: brain atlas, brain sections, database, on-line resources
Brain Maps is a huge on-line database of brain sections at extreme high resolution. Physical and digital sliced brains are available to download and to explore at macroanatomical and cellular levels. Brain atlases are interactive, and images are available for research and for teaching, with applications and annotations, in two and three dimensions. This is an amazing resource!
I have added three webpages to my sidebar, collections of graphics on brain and skull. Skull-a-day is a wonderful anthology of art and anatomy. Craniophiles is a real skullology blog. Headbrain is a very effective source of perspectives in … functional craniology! Art can supply powerful iconographic supports, but it can also provide a different and alternative view, transmitting concepts which can barely be described by words or numbers.