Butler Ann B
Department of Molecular Neuroscience, George Mason University, Fairfax, VA, USA.
Brain Behav Evol. 2017;90(1):7-14. doi: 10.1159/000475981. Epub 2017 Sep 4.
The hippocampus was first named in mammals based on the appearance of its gross morphological features, one end of it being fancied to resemble the head of a horse and the rest of it a silkworm, or caterpillar. A hippocampus, occupying the most medial part of the telencephalic pallium, has subsequently been identified in diverse nonmammalian taxa, but in which the "horse-caterpillar" morphology is lacking. While some strikingly similar functional similarities have been identified, questions of its homology ("sameness") across these taxa and about the very fundamental relationship of structure to function in central nervous system structures remain open. The hippocampal formation of amniotes participates in allocentric (external landmark) spatial navigation, memory, and attention to novel stimuli, and these functions generally are shared across amniotes despite variation in its morphological features. Substantially greater deviation in its morphology occurs in anamniotes, including amphibians and ray-finned fishes (actinopterygians), but its functions of allocentric spatial navigation and/or memory have been found to be preserved by studies in these taxa. Its shared functional roles cannot be used as evidence of structural homology, but given that other criteria indicate homology of the medial pallial derivative across these clades, the similar functions themselves may be regarded as homologous functions if they are based on the same cellular mechanisms and connections. The question arises as to whether the similar functions are performed by as yet undiscovered, shared morphological features or by different features that accomplish the same results via different mechanisms of neural function.
海马体最初是根据其大体形态特征在哺乳动物中命名的，它的一端被想象成类似马头，其余部分类似蚕或毛虫。海马体位于端脑皮层的最内侧部分，随后在多种非哺乳动物类群中也被发现，但这些类群中缺乏“马 - 毛虫”形态。虽然已经发现了一些惊人的功能相似性，但关于这些类群中海马体的同源性（“相同性”）以及中枢神经系统结构中结构与功能的根本关系问题仍然没有答案。羊膜动物的海马结构参与以自我为中心（外部地标）的空间导航、记忆以及对新刺激的关注，尽管其形态特征存在差异，但这些功能在羊膜动物中通常是共有的。在无羊膜动物中，包括两栖动物和辐鳍鱼类（硬骨鱼），其形态差异要大得多，但这些类群的研究发现其以自我为中心的空间导航和/或记忆功能得以保留。其共享的功能作用不能作为结构同源性的证据，但鉴于其他标准表明这些进化枝中内侧皮层衍生物具有同源性，如果相似功能基于相同的细胞机制和连接，那么这些相似功能本身可以被视为同源功能。问题在于，这些相似功能是由尚未发现的共享形态特征执行的，还是由通过不同神经功能机制实现相同结果的不同特征执行的。
