Gaffan D, Hornak J
Department of Experimental Psychology, Oxford University, UK.
Philos Trans R Soc Lond B Biol Sci. 1997 Oct 29;352(1360):1481-8. doi: 10.1098/rstb.1997.0135.
Hippocampal damage in people causes impairments of episodic memory, but in rats it causes impairments of spatial learning. Experiments in macaque monkeys show that these two kinds of impairment are functionally similar to each other. After any lesion that interrupts the Delay-Brion system (hippocampus, fornix, mamillary bodies and anterior thalamus) monkeys are impaired in scene-specific memory, where an event takes place against a background that is specific to that event. Scene-specific memory in the monkey corresponds to human episodic memory, which is the memory of a unique event set in a particular scene, as opposed to scene-independent human knowledge, which is abstracted from many different scenes. However, interruption of the Delay-Brion system is not sufficient to explain all of the memory impairments that are seen in amnesic patients. To explain amnesia the specialized function of the hippocampus in scene memory needs to be considered alongside the other, qualitatively different functional specializations of other memory systems of the temporal lobe, including the perirhinal cortex and the amygdala. In all these specialized areas, however, including the hippocampus, there is no fundamental distinction between memory systems and perceptual systems. In explaining memory disorders in amnesia it is also important to consider them alongside the memory disorders of neglect patients. Neglect patients fail to represent in memory the side of the world that is contralateral to the current fixation point, in both short- and long-term memory retrieval. Neglect was produced experimentally by unilateral visual disconnection in the monkey, confirming the idea that visual memory retrieval is retinotopically organized; patients with unilateral medial temporal-lobe removals showed lateralized memory impairments for half-scenes in the visual hemifield contralateral to the removal. Thus, in scene-memory retrieval the Delay-Brion system contributes to the retrieval of visual memories into the retinotopically organized visual cortex. This scene memory interpretation of hippocampal function needs to be contrasted with the cognitive-map hypothesis. The cognitive-map model of hippocampal function shares some common assumptions with the Hebb-synapse model of association formation, and the Hebb-synapse model can be rejected on the basis of recent evidence that monkeys can form direct associations in memory between temporally discontiguous events. Our general conclusion is that the primate brain encompasses widespread and powerful memory mechanisms which will continue to be poorly understood if theory and experimentation continue to concentrate too much, as they have in the past, on the hippocampus and the Hebb synapse.
人类海马体损伤会导致情景记忆受损，但在大鼠中，海马体损伤会导致空间学习能力受损。猕猴实验表明，这两种损伤在功能上彼此相似。在任何中断延迟-布里昂系统（海马体、穹窿、乳头体和前丘脑）的损伤后，猴子在特定场景记忆方面会出现障碍，即一个事件发生在特定于该事件的背景中。猴子的特定场景记忆对应于人类的情景记忆，即对特定场景中独特事件的记忆，这与从许多不同场景中抽象出来的与场景无关的人类知识形成对比。然而，延迟-布里昂系统的中断不足以解释失忆症患者中出现的所有记忆障碍。为了解释失忆症，需要将海马体在场景记忆中的特殊功能与颞叶其他记忆系统（包括嗅周皮质和杏仁核）在性质上不同的其他特殊功能一起考虑。然而，在所有这些特殊区域，包括海马体，记忆系统和感知系统之间没有根本区别。在解释失忆症中的记忆障碍时，将它们与忽视患者的记忆障碍一起考虑也很重要。忽视患者在短期和长期记忆检索中，都无法在记忆中呈现与当前注视点对侧的世界部分。通过在猴子身上进行单侧视觉切断实验产生了忽视现象，这证实了视觉记忆检索是按视网膜拓扑组织的观点；单侧内侧颞叶切除的患者在切除对侧的视觉半视野中的半场景中表现出侧向记忆障碍。因此，在场景记忆检索中，延迟-布里昂系统有助于将视觉记忆检索到按视网膜拓扑组织的视觉皮层中。这种对海马体功能的场景记忆解释需要与认知地图假说进行对比。海马体功能的认知地图模型与联想形成的赫布突触模型有一些共同假设，而基于最近的证据，即猴子可以在记忆中形成时间上不连续事件之间的直接联想，赫布突触模型可以被否定。我们的总体结论是，如果理论和实验继续像过去那样过于集中在海马体和赫布突触上，灵长类动物大脑中广泛而强大的记忆机制将继续难以被理解。
