Laboratory of Psychobiology, Universidad de Sevilla, Seville, Spain.
Brain Struct Funct. 2022 Nov;227(8):2879-2890. doi: 10.1007/s00429-022-02553-3. Epub 2022 Aug 25.
There is an ongoing debate on the evolutionary origin of the episodic memory function of the hippocampus. A widely accepted hypothesis claims that the hippocampus first evolved as a dedicated system for spatial navigation in ancestral vertebrates, being transformed later in phylogeny to support a broader role in episodic memory with the emergence of mammals. On the contrary, an alternative hypothesis holds that the hippocampus of ancestral vertebrates originally encoded both the spatial and temporal dimensions of relational memories since its evolutionary appearance, thus suggesting that the episodic-like memory function of the hippocampus could be the primitive condition in vertebrate forebrain evolution. The present experiment was aimed at scrutinizing these opposing hypotheses by investigating whether the hippocampal pallium of teleost fish, a vertebrate group that shares with mammals a common ancestor that lived about 400 Mya, is, like the hippocampus of mammals, essential to associate time-discontiguous events. Thus, goldfish with lesions in the ventral part of the dorsolateral pallium (Dlv), a telencephalic region considered homologous to the hippocampal pallium of land vertebrates, were trained in trace versus delay eyeblink-like classical conditioning, two learning procedures that differ only in the temporal relationships between the stimuli to be associated in memory. The results showed that hippocampal pallium lesion in goldfish severely impairs trace conditioning, but spares delay conditioning. This finding challenges the idea that navigation preceded relational memory in evolutionary appearance and suggests the possibility that a relational memory function that associates the experienced events in both the spatial and temporal dimensions could be a primitive feature of the hippocampus that pre-existed in the common ancestor of vertebrates.
对于海马体的情景记忆功能的进化起源，一直存在着争论。一个被广泛接受的假说声称，海马体最初是作为祖先脊椎动物的空间导航专用系统进化而来的，后来在进化过程中，随着哺乳动物的出现，它的功能逐渐扩展到情景记忆。相反，另一个假说认为，祖先脊椎动物的海马体从其出现开始就编码了空间和时间维度的关系记忆，因此，情景记忆功能可能是脊椎动物前脑进化的原始状态。本实验旨在通过研究硬骨鱼的脑侧体背侧部腹侧（Dlv）的损伤是否像哺乳动物的海马体一样，对于将不连续的时间事件联系起来是必需的，来仔细研究这些相互矛盾的假说。硬骨鱼是与哺乳动物具有共同祖先的脊椎动物，这个共同祖先生活在大约 4 亿年前。因此，我们对脑侧体背侧部腹侧受损的金鱼进行了痕迹与延迟类眨眼式经典条件反射训练，这两种学习程序仅在要在记忆中关联的刺激之间的时间关系上有所不同。结果表明，金鱼的脑侧体背侧部腹侧损伤严重损害了痕迹条件反射，但对延迟条件反射没有影响。这一发现挑战了导航先于关系记忆的进化出现的观点，并表明将空间和时间维度中经历的事件联系起来的关系记忆功能可能是脊椎动物共同祖先中存在的海马体的原始特征。
