Rilling & Insel have argued that in primates, bigger brains have proportionally fewer anatomical interhemispheric connections, leading to reduced functional connectivity between the hemispheres. They based this on a comparison between surface areas of the corpus callosum and cortex rather than estimating connection counts, while leaving out other quantities also dependent on brain size such as callosal fiber density, neuron density, and number of functional areas. We use data from the literature to directly estimate connection counts. First, we estimate callosal fiber density as a function of brain size. We validate this by comparing out-of-sample human data to our function's estimate. We then mine the literature to obtain function estimates for all other quantities, and use them to estimate intra- and interhemispheric white matter connection counts as a function of brain size. The results show a much larger decrease in the scaling of interhemispheric to intrahemispheric connections than previously estimated. However, we hypothesize that raw connection counts are the wrong quantity to be estimating when considering functional connectivity. Instead, we hypothesize that functional connectivity is related to connection counts relative to the number of cortical areas. Accordingly, we estimate inter-area connection counts for intra- and interhemispheric connectivity and find no difference in how they scale with brain size. We find that, on average, an interhemispheric inter-area connection contains 3-8x more connections than an intrahemispheric inter-area connection, regardless of brain size. In doing so, we find that the fiber count of the human corpus callosum has been underestimated by 20%.

中文翻译：

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半球之间的连通性在整个物种中持续存在：call体上的异位暴露

Rilling＆Insel认为，在灵长类动物中，较大的大脑在解剖上的半球之间的连接成比例地减少，从而导致半球之间的功能连接性降低。他们基于this体和皮质表面积之间的比较，而不是估计连接数，而忽略了其他数量，这也取决于大脑的大小，例如call纤维密度，神经元密度和功能区域的数量。我们使用文献中的数据直接估算连接数。首先，我们估计call纤维密度是脑大小的函数。我们通过将样本外的人类数据与我们的职能估算值进行比较来验证这一点。然后，我们挖掘文献以获得所有其他数量的函数估计，并使用它们来估计与大脑大小有关的大脑内和大脑半球之间的白质连接计数。结果表明，与以前估计的相比，半球到半球之间的连接比例的减小幅度更大。但是，我们假设在考虑功能连接性时，原始连接数是错误的数量。相反，我们假设功能连通性与相对于皮质区域数量的连接计数有关。因此，我们估计了半球内和半球之间连接的区域间连接计数，并且发现它们与大脑大小的比例关系没有差异。我们发现，平均而言，与大脑内区域间连接相比，半球形区域间连接所包含的连接要多3-8倍，而不管大脑的大小如何。在这样做，