Tanaka Kazumasa Z, McHugh Thomas J
Laboratory for Circuit and Behavioral Physiology, RIKEN Center for Brain Science, Wako, Japan.
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan.
J Exp Neurosci. 2018 Dec 2;12:1179069518815942. doi: 10.1177/1179069518815942. eCollection 2018.
The hippocampus encodes memories for past events, but the nature of the hippocampal code subserving this function remains unclear. A prevailing idea, strongly supported by hippocampal physiology, is the Cognitive Map Theory. In this view, episodic memories are anchored to spatial domains, or allocentric frameworks, of experiences, with the hippocampus providing a stable representation of external space. On the other hand, recent studies using Immediate Early Genes (IEGs) as a proxy of neuronal activation support the Memory Index Theory. This idea posits that the hippocampal memory trace serves as an index for a cortical representation of memory (a map for internal representation) and hypothesizes the primary hippocampal function is to reinstate the pattern of cortical activity present during encoding. Our recent findings provide a unitary view on these two fundamentally different theories. In the hippocampal CA1 region the activity of c-Fos expressing pyramidal neurons reliably reflects the identity of the context the animal is experiencing in an index-like fashion, while spikes from other active pyramidal cells provide spatial information that is stable over a long period of time. These two distinct ensembles of hippocampal neurons suggest heterogeneous roles for subsets of hippocampus neurons in memory.
海马体对过去事件的记忆进行编码，但其支持该功能的编码本质仍不清楚。一种得到海马体生理学有力支持的主流观点是认知地图理论。按照这种观点，情景记忆锚定于体验的空间域或空间参照系，海马体提供外部空间的稳定表征。另一方面，最近使用即刻早期基因（IEGs）作为神经元激活指标的研究支持记忆索引理论。该理论认为，海马体记忆痕迹作为记忆皮层表征的索引（内部表征的地图），并假设海马体的主要功能是恢复编码期间存在的皮层活动模式。我们最近的研究结果为这两种根本不同的理论提供了统一的观点。在海马体CA1区域，表达c-Fos的锥体神经元的活动以类似索引的方式可靠地反映动物正在经历的环境的身份，而其他活跃锥体细胞的尖峰提供长时间稳定的空间信息。海马体神经元的这两个不同集合表明海马体神经元亚群在记忆中具有不同的作用。
