Department of Human Evolutionary Biology, Harvard University, 11 Divinity Ave, Cambridge, MA, 02138, USA.
National Institute of Mental Health, National Institutes of Health, Bethesda, MD, 20814, USA.
Brain Struct Funct. 2020 Nov;225(8):2521-2531. doi: 10.1007/s00429-020-02139-x. Epub 2020 Sep 9.
The hippocampal formation is important for higher brain functions such as spatial navigation and the consolidation of memory, and it contributes to abilities thought to be uniquely human, yet little is known about how the human hippocampal formation compares to that of our closest living relatives, the chimpanzees. To gain insight into the comparative organization of the hippocampal formation in catarrhine primates, we quantified neurons stereologically in its major subdivisions-the granular layer of the dentate gyrus, CA4, CA2-3, CA1, and the subiculum-in archival brain tissue from six chimpanzees ranging from 29 to 43 years of age. We also sought evidence of Aβ deposition and hyperphosphorylated tau in the hippocampus and adjacent neocortex. A 42-year-old animal had moderate cerebral Aβ-amyloid angiopathy and tauopathy, but Aβ was absent and tauopathy was minimal in the others. Quantitatively, granule cells of the dentate gyrus were most numerous, followed by CA1, subiculum, CA4, and CA2-3. In the context of prior investigations of rhesus monkeys and humans, our findings indicate that, in the hippocampal formation as a whole, the proportions of neurons in CA1 and the subiculum progressively increase, and the proportion of dentate granule cells decreases, from rhesus monkeys to chimpanzees to humans. Because CA1 and the subiculum engender key hippocampal projection pathways to the neocortex, and because the neocortex varies in volume and anatomical organization among these species, these findings suggest that differences in the proportions of neurons in hippocampal subregions of catarrhine primates may be linked to neocortical evolution.
海马体对于空间导航和记忆巩固等高级大脑功能至关重要，并且有助于被认为是人类独有的能力，但我们对人类海马体与我们最亲近的亲属——黑猩猩的海马体相比有何不同知之甚少。为了深入了解在灵长类动物中海马体的比较组织，我们在六个年龄在 29 至 43 岁的黑猩猩的存档脑组织中，通过立体学方法对其主要分区——齿状回颗粒层、CA4、CA2-3、CA1 和下托——中的神经元进行了定量。我们还寻找了海马体和相邻新皮层中 Aβ 沉积和过度磷酸化 tau 的证据。一只 42 岁的动物患有中度脑 Aβ-淀粉样血管病和 tau 病，但在其他动物中，Aβ 缺失且 tau 病很少见。定量分析表明，齿状回的颗粒细胞数量最多，其次是 CA1、下托、CA4 和 CA2-3。在恒河猴和人类的先前研究背景下，我们的发现表明，在整个海马体中，CA1 和下托中的神经元比例从恒河猴到黑猩猩再到人类逐渐增加，而齿状回颗粒细胞的比例逐渐减少。由于 CA1 和下托产生了关键的海马体投射途径到新皮层，并且由于这些物种的新皮层在体积和解剖结构上存在差异，因此这些发现表明，灵长类动物海马体各分区神经元比例的差异可能与新皮层的进化有关。
