Sharp P E
Department of Psychology, Yale University, New Haven, Connecticut 06520-8205, USA.
Hippocampus. 1999;9(4):432-43. doi: 10.1002/(SICI)1098-1063(1999)9:4<432::AID-HIPO9>3.0.CO;2-P.
At least two important questions are posed by the existence of hippocampal place cells. The first of these has to do with how the complex, abstract properties exhibited by these cells can be explained mechanistically. The second has to do with the implications of place cells for our conception of the broader role of the hippocampus in spatial and other behaviors. Here, evidence is reviewed that: (1) Hippocampal cells show different "maps" (place cell representations) for each environment the animal visits and, in fact, can show multiple maps even for any one environment. The choice of the current map for any one environment depends on environmental, contextual, and event-related variables. (2) Cells in the subiculum and entorhinal cortex also show location-specific firing patterns (like hippocampal place cells), but show the same pattern for each environment the animal visits. A model is presented that is a variant of hippocampus-based path integration models developed by McNaughton and colleagues. In this version, the subiculum and entorhinal cortex work together to form a single, universal map that is used for each environment, and that can exhibit path integration abilities. The universal subicular/entorhinal representation is postulated to assist the hippocampal layer to rapidly form new environment and context specific "maps" for each new environment/temporal context ("episode") the animal experiences. In this view, hippocampal layer activity is always obligatorily spatial, due to the input from the entorhinal universal "map." However, the fact that the hippocampus generates a new map in response to global, non-spatial, contextual attributes of each situation, means that the hippocampus is always coding non-spatial aspects of a situation using its obligatorily spatial code. This brings the hippocampal place cell activity in to line with the broader role that has been postulated for the hippocampus in learning and memory functions.
海马体位置细胞的存在引发了至少两个重要问题。第一个问题涉及如何从机制上解释这些细胞所展现出的复杂、抽象特性。第二个问题则关乎位置细胞对于我们理解海马体在空间及其他行为中更广泛作用的意义。在此,我们回顾相关证据:(1) 海马体细胞针对动物所进入的每个环境展现出不同的“地图”(位置细胞表征),事实上,即使对于任何一个环境,也能展现出多个地图。针对任何一个环境当前地图的选择取决于环境、情境及与事件相关的变量。(2) 下托和内嗅皮质中的细胞也呈现出位置特异性放电模式(类似于海马体位置细胞),但对于动物所进入的每个环境都呈现相同的模式。本文提出了一个模型,它是由麦克诺顿及其同事开发的基于海马体的路径整合模型的一个变体。在此版本中,下托和内嗅皮质协同工作以形成一个单一的通用地图,该地图用于每个环境,并且能够展现路径整合能力。假定通用的下托/内嗅表征有助于海马层为动物所经历的每个新环境/时间情境(“事件”)快速形成新的环境及情境特异性“地图”。按照这种观点,由于来自内嗅通用“地图”的输入,海马层活动始终必然是空间性的。然而,海马体根据每种情境的全局、非空间、情境属性生成新地图这一事实意味着,海马体始终在利用其必然的空间编码对情境的非空间方面进行编码。这使得海马体位置细胞的活动与为海马体在学习和记忆功能中所假定的更广泛作用相一致。