Tag Archives: brain size

Brain regional scaling

Reardon and colleagues recently published a study on the variation of human brain organization and its relationship with brain size. Using neuroimaging data from more than 3000 individuals they calculated the local surface area and estimated the areal scaling in relation to the total cortical area in order to generate a reference map for areal scaling in cortical and subcortical structures. By using three separate cohorts, three different platforms of image-acquisition, and two distinct imaging processing pipelines, they obtained the same results. Regions with positive scaling, i.e. which area increases with increasing total cortical size, were found with the prefrontal, lateral temporoparietal, and medial parietal cortices, whereas the limbic, primary visual, and primary somatosensory regions showed negative scaling. These patterns of cortical area distribution relatively to normative brain size variation were also reproduced at the individual level in terms of proportion, as, for instance, areas of positive scaling regions were positively correlated with the total cortical area. These patterns of areal scaling distribution are also comparable with patterns of brain expansion during human development and primate evolution (humans vs. macaques). In terms of cytoarchitecture, the regions of positive scaling were concentrated within association cortices, such as the default mode, dorsal attention, and frontoparietal networks, while the negative scaling regions were found within the limbic network. The association of areal scaling patterns with known patterns of mitochondria-related gene expression suggests these regions that are expanded in larger brains might differ in their metabolic profile. The authors concluded that the similarity of the areal scaling maps across development and evolution, and at the individual level, suggests a shared scaling gradient of the primate cortex. Larger brains tend to preferentially expand association cortex, specialized for integration of information, which might point to a need for an increase of the neural subtracts, such as dendrites or synapses, in order to maintain or enhance brain function in an expanded brain. Further study designs are required to investigate the relationship between cortical areal patterns and brain function.

Sofia Pedro

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Estimating cranial capacity

Jingchuan 1 (Yameng Zhang)Cranial capacity is one of the most studied features used in human paleoneurology. According to the completeness of the fossil skulls, direct or indirect methods have been used in estimating the cranial capacity, including water displacement, seeds, and regression statistics. However, two problems always exist when dealing with fossil skulls: the incompleteness of the specimens and the small sample size. Both limits can introduce an important uncertainty when making inferences on cranial capacity through quantitative approaches. In a recent paper published in Quaternary International we improved traditional methods for estimating cranial capacity by using measurements on brain endocast instead of skull, and by using multivariate statistical method such as Principal Component Regression (PCR) and Partial Least Square Regression (PLSR) instead of simple linear models. In this study, modern human skulls and endocasts are used as training and test data. We then applied these methods on three Homo erectus specimens and one Late Pleistocene Homo sapiens individual. When compared with traditional ones, these methods show higher reliability, and the error of the estimations approaches 50 cc. This study stresses further the importance of methodological research and correlation analysis in paleoneurology.

Yameng Zhang