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

https://doi.org/10.1016/j.pneurobio.2022.102217Get rights and content
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Highlights

  • The fasciola cinereum (FC) is an independent subregion of the hippocampus by itself.

  • The FC sends its major outputs only to the dentate gyrus in the hippocampus.

  • The FC is critical for the acquistion of visual contextual memory.

  • Place cells fire in their place fields for a limited time period only in the FC.

Abstract

The fasciola cinereum (FC) is a subregion of the hippocampus that has received relatively little attention compared with other hippocampal subregions with respect to anatomical characteristics and functional significance. Here, we show that the FC exhibits clear anatomical borders with the distalmost region of the CA1. Principal neurons in the FC resemble the granule cells in the dentate gyrus (DG). However, adult neurogenesis was not found unlike in the DG. The FC receives inputs mostly from the lateral entorhinal cortex and perirhinal cortex while projecting exclusively to the crest of the DG within the hippocampus. Neurotoxic lesions in the FC using colchicine impaired the acquisition, but not retrieval, of visual contextual memory in rats. FC lesions also impaired place recognition and object-in-place memory. As the rat performed the contextual memory task on the T-maze, place cells in the FC exhibited robust place fields and were indiscriminable from those in CA1 with respect to the basic firing properties. However, place cells in the FC fired only transiently in their place fields on the maze compared with those in CA1. Our findings suggest that the episodic firing patterns of the place cells in the FC may play critical roles in learning a novel contextual environment by facilitating temoporally structured contextual pattern separation in the DG of the hippocampus.

Abbreviations

dCA1
distal CA1
DG
dentate gyrus
dmCA1
distalmost CA1
FC
fasciola cinereum
GCL
granule cell layer
ISI
inter-spike interval
LEC
lateral entorhinal cortex
LFP
Local field potential
MEC
medial entorhinal cortex
ML
molecular layer
MTL
medial temporal lobe
PER
perirhinal cortex
POR
postrhinal cortex
PBS
phosphate-buffered saline
RBs
Retrobeads
RGS14
regulator of G-protein signaling 14
RMI
rate modulation index
SEM
standard error of mean
STD
standard deviation
SWR
sharp-wave ripple
WFS1
Wolfram syndrome 1

Keywords

Hippocampus
Spatial memory
Place cell
Contextual memory
Pattern separation
Dentate gyrus

Cited by (0)

1

Present address: Krieger Mind/Brain Institute, Johns Hopkins University, 3400 N. Charles Street, Baltimore MD, USA 21218.

2

Present address: FAU Brain Institute, Florida Atlantic University, 5353 Parkside Drive, Jupiter, FL, USA 33458.

3

Present address: Fluorescence Core Imaging Center Ewha Womans University 52, Ewhayeodae-gil, Seodaemun-gu, Seoul, Korea 03760.