On How the Dentate Gyrus Contributes to Memory Discrimination

Abstract

The dentate gyrus (DG) is crucial for behaviorally discriminating similar spatial memories, predicting that DG place cells change ("remap") their relative spatial tuning ("place fields") for memory discrimination. This prediction was never tested, although DG place cells remap across similar environments without memory tasks. We confirm this prior finding but find that DG place fields do not remap across spatial tasks that require DG-dependent memory discrimination. Instead of remapping, place-discriminating discharge is observed transiently among DG place cells, particularly when memory discrimination is most necessary. The DG network may signal memory discrimination by expressing distinctive sub-second network patterns of co-firing at memory discrimination sites. This involves increased coupling of discharge from place cells and interneurons, as was observed during successful, but not failed, behavioral expression of memory discrimination. Instead of remapping, these findings indicate that memory discrimination is signaled by sub-second patterns of correlated discharge within the dentate network.

Learning to learn persistently modifies an entorhinal-hippocampal excitatory-inhibitory subcircuit

“…The task requires intact hippocampal activity 7,8 , and persistent PKMzeta (PKMζ)-mediated long-term potentiation (LTP) of hippocampal synaptic function [9][10][11] . Hippocampus place cell discharge during the task mirrors ongoing performance as well as cognitive control of switching between task relevant and irrelevant information, demonstrating representational multi-tasking [12][13][14] . Furthermore, resembling effective CBT, preemptive training is sufficient to prevent subsequent neuropsychiatric-related cognitive impairments in a neurodevelopmental rat model 15 .…”

“…The cognitive control training (CCT) group was trained in the R+A-active place avoidance task variant that is predicted to cause learning to learn. Mice on a rotating (1 rpm) arena learn the room-based location of a stationary shock zone, and must ignore the arena-based, unpredictable locations where they experience shock 16 , although hippocampus discharge represents these places 12,13 . Mice in the place learning (PL) control group were trained in the R+ task variant that differs from the R+A-task variant by the presence of shallow water on the arena surface 16 .…”

“…DG interneurons strongly regulate principal cell firing in freely-behaving rats 22 . CCT increases the sub-second coupling between action potential discharge of excitatory granule cells and inhibitory neurons in DG 12 , and spatial learning increases DG mossy fiber-mediated feedforward inhibition 23 , motivating us to hypothesize that CCT increases DG inhibition. Gad2Cre-ChR2-eYFP mice expressing the excitatory opsin in GABAergic neurons were used to test two predictions of this hypothesis ( Fig.…”

Hippocampal formation volume, its subregions, and its specific contributions to visuospatial memory tasks

“…They are located near each other, have similar cytoarchitecture, and are involved in related functions (7). The dentate gyrus is the entrance region of the hippocampal formation, meaning it works as a pre-processor of received information by encoding this information and preparing it for further processing in the Ammon's Horn (30). The dentate gyrus is essential to the behavioral discrimination of similar spatial components of memory functions.…”

How the Hippocampus Represents Memories: Making Sense of Memory Allocation Studies

“…This implies that the neurons overexpressing CREB that won the competition and took part in the encoding must have the corresponding stimulus they are encoding, or at least something similar to it (i.e., with many of the same features involved), somewhere in their receptive fields. Therefore, artificial manipulations lead to neurons in the assembly being “replaced” (compared to natural assemblies) by other neurons representing qualitatively similar information, and such changes may also preserve features such as the temporal structure of assembly firing, which can convey important information . Therefore, normal and artificially manipulated assemblies should encode qualitatively similar representations, so we would expect that behaviors displayed by the animal in response to those two possible neuronal assemblies are also similar.…”