School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, Parktown, Johannesburg, Republic of South Africa.
J Comp Neurol. 2012 Aug 1;520(11):2430-9. doi: 10.1002/cne.23046.
This study provides quantitative data on the extent of gyrencephaly in the large-brained African elephant and several species of cetaceans (from smaller to larger brained) in comparison with other mammals. Across three mammalian orders (primates, carnivores, and artiodactyls), the species with the larger brains are more gyrencephalic with each order, exhibiting a specific negative allometry. The African elephant, with a 5-kg brain, has a gyrencephalic index (GI) of 3.89, which, though highly gyrencephalic, is not more so than would be predicted for a mammal with a 5-kg brain. The cetaceans had an average GI of 5.43, are the most gyrencephalic mammals studied to date, and are more gyrencephalic than one would predict based on comparison with other mammals. No relationship between brain mass and GI was evident in the cetaceans as seen in other mammals, with all cetaceans showing similar GIs irrespective of brain mass (range of GI 5.23-5.70, range of brain mass 577-5617 g). This is yet another parameter indicating cetaceans to be neuroanatomical outliers. Two species of pinnipeds studied had GIs that were well above those seen for terrestrial carnivores, and the aquatic manatee was close to lissencephalic. Thus, all three groups of marine mammals showed unusual extents of cortical gyrencephaly, indicating a morphological alteration of the telencephalon associated with the return to the marine environment. The analysis suggests that cortical thickness and neuronal density are important factors in determining the extent of gyrencephaly across mammalian species.
本研究提供了量化数据，比较了大型非洲象和几种鲸目动物（从较小到较大脑）的脑回数量，与其他哺乳动物相比。在三个哺乳动物目（灵长目、食肉目和偶蹄目）中，脑容量较大的物种在每个目中的脑回数量都更多，表现出特定的负异速生长。非洲象的大脑重 5 公斤，脑回指数（GI）为 3.89，尽管高度脑回化，但并不超过预期的 5 公斤大脑的哺乳动物。鲸目动物的平均 GI 为 5.43，是迄今为止研究过的最脑回化的哺乳动物，比根据与其他哺乳动物的比较预测的更脑回化。在鲸目动物中，脑质量和 GI 之间没有明显的关系，这与其他哺乳动物一样，所有鲸目动物的 GI 相似，而与脑质量无关（GI 范围为 5.23-5.70，脑质量范围为 577-5617 克）。这是另一个表明鲸目动物是神经解剖学异常的参数。研究的两种鳍足类动物的 GI 远高于陆地食肉动物，而水生海牛则接近平滑脑。因此，所有三组海洋哺乳动物都表现出不寻常的大脑回数量，表明与返回海洋环境相关的端脑形态发生了改变。该分析表明，皮质厚度和神经元密度是决定哺乳动物物种脑回数量的重要因素。
