Hippocampal projections to the anterior olfactory nucleus differentially convey spatiotemporal information during episodic odour memory

Afif J Aqrabawi,Jun Chul Kim

doi:10.1038/s41467-018-05131-6

Abstract

The hippocampus is essential for representing spatiotemporal context and establishing its association with the sensory details of daily life to form episodic memories. The olfactory cortex in particular shares exclusive anatomical connections with the hippocampus as a result of their common evolutionary history. Here we selectively inhibit hippocampal projections to the anterior olfactory nucleus (AON) during behavioural tests of contextually cued odour recall. We find that spatial odour memory and temporal odour memory are independently impaired following inhibition of distinct, topographically organized hippocampal-AON pathways. Our results not only reveal a longstanding unknown function for the AON but offer new mechanistic insights regarding the representation of odours in episodic memory.

Highlights

The hippocampus is essential for representing spatiotemporal context and establishing its association with the sensory details of daily life to form episodic memories
We found that the anterior olfactory nucleus (AON) exhibits a widespread increase in c-Fos-positive neurons following exposure to a novel context-odour pairing, yet neither stimulus alone was sufficient to evoke an increase in the number of labelled cells compared with homecage controls (Supplementary Fig. 1)
These results are in line with previous work on the response properties of AON principal cells and suggest that the AON has a role in context-odour coincidence detection[20,21]

Summary

Introduction

The hippocampus is essential for representing spatiotemporal context and establishing its association with the sensory details of daily life to form episodic memories. We selectively inhibit hippocampal projections to the anterior olfactory nucleus (AON) during behavioural tests of contextually cued odour recall. An emerging theory holds that the HPC conducts this retrieval process by reinstating patterns of cortical activity observed during learning[11,12]. It is not known how hippocampal transmission of contextual information can reproduce the sensory aspects of episodic memory. Hippocampal projections to the olfactory cortex offer a unique experimental model for understanding the context-driven recollection of previously encountered sensory stimuli. We revealed a dense and topographically organized projection from the dorsoventral extent of the HPC to the anterior olfactory nucleus (AON)[15] (Fig. 1a). The AON is an ideal site of convergence for olfactory and contextual information given its anatomical position as the initial recipient of input from the olfactory bulb and the largest source a rf D M

Methods

Results

Conclusion