The fasciola cinereum subregion of the hippocampus is important for the acquisition of visual contextual memory

Abstract

The fasciola cinereum (FC) is a small subregion of the hippocampus that has been relatively unattended and less known compared with other subregions with respect to anatomical characteristics and functional significance. The lack of a detailed anatomical characterization of the FC has created ambiguity in the literature regarding the definition of FC borders with the CA1 subregion and attribution of cognitive functions to specific subregions of the hippocampus. Here, we show that the anatomical borders of the FC can be clearly defined histologically, and the region itself is characterized by unique anatomical connections and physiological properties. The major output of the FC is to the dentate gyrus (DG) and the FC itself. Firing properties of cells recorded from the FC were different from those in the CA1, and no sign of neurogenesis was detected in the FC. Selective ablation of neurons in the FC, successfully accomplished using colchicine, significantly impaired acquisition of novel visual-contextual memory in rats, without affecting retrieval of familiar visual-contextual memories. Our findings suggest that, given its connections to the DG, the FC may play critical roles in learning novel contextual behavior.

Spatial Atlas of the Mouse Central Nervous System at Molecular Resolution

“…2d, slices 2-3, 11-15), which may be related to the homologous developmental origins of the isocortex and allocortex 31, 33 . As another example, in the hippocampal area, the CA2 pyramidal layer exhibits a high resemblance with the indusium griseum (IG) and the fasciola cinerea (FC) in molecular expression, agreeing with previous reports 34, 35 (region CA2_IG_FC, marked by Neurod6 + Rgs14 + TEGLU_6; Fig. 2d, slices 1, 8, 11- 12).…”

Further refining the boundaries of the hippocampus CA2 with gene expression and connectivity: Potential subregions and heterogeneous cell types

“…However, recent studies examining the relationship of CA2, FC, and IG suggest that the FC and IG are independent hippocampal subregions and not extensions of the CA2 based on connectivity and morphological characteristics as well as developmental differences in Pcp4 molecular expression (Park et al, 2022;Sanders et al, 2020).…”

“…Therefore, the CA2 boundaries extend nearly to the rostral tip of the hippocampus where CA2 gene expression patterns adjoin similarly expressed cells of the fasciola cinerea (FC) and induseum griseum (IG) which appears to form a single continuous cellular layer of gene expression. However, recent studies examining the relationship of CA2, FC, and IG suggest that the FC and IG are independent hippocampal subregions and not extensions of the CA2 based on connectivity and morphological characteristics as well as developmental differences in Pcp4 molecular expression (Park et al, 2022; Sanders et al, 2020).…”