# A hippocampus-accumbens code guides goal-directed appetitive behavior

## TL;DR

This study reveals how a specific brain pathway helps mice navigate to rewards by combining spatial and behavioral information.

## Contribution

The study identifies a novel hippocampal subpopulation projecting to the nucleus accumbens with enhanced conjunctive coding for spatial and behavioral states.

## Key findings

- Optogenetic stimulation of the dHPC→NAc pathway is necessary and sufficient for spatial memory-related appetitive behaviors.
- dHPC→NAc neurons show enhanced spatial tuning and coding of non-spatial task-relevant behaviors like deceleration and licking.
- A generalized linear model shows improved reward zone identification via conjunctive coding in dHPC→NAc neurons.

## Abstract

The dorsal hippocampus (dHPC) is a key brain region for the expression of spatial memories, such as navigating towards a learned reward location. The nucleus accumbens (NAc) is a prominent projection target of dHPC and implicated in value-based action selection. Yet, the contents of the dHPC→NAc information stream and their acute role in behavior remain largely unknown. Here, we found that optogenetic stimulation of the dHPC→NAc pathway while mice navigated towards a learned reward location was both necessary and sufficient for spatial memory-related appetitive behaviors. To understand the task-relevant coding properties of individual NAc-projecting hippocampal neurons (dHPC→NAc), we used in vivo dual-color two-photon imaging. In contrast to other dHPC neurons, the dHPC→NAc subpopulation contained more place cells, with enriched spatial tuning properties. This subpopulation also showed enhanced coding of non-spatial task-relevant behaviors such as deceleration and appetitive licking. A generalized linear model revealed enhanced conjunctive coding in dHPC→NAc neurons which improved the identification of the reward zone. We propose that dHPC routes specific reward-related spatial and behavioral state information to guide NAc action selection.

The dorsal hippocampus plays an important role for spatial memory, but how its outputs guide behavior is not fully understood. Here, the authors show that nucleus accumbens-specific hippocampal projection neurons carry a highly conjunctive code of spatial and action information that directs spatial reward memory-guided appetitive behaviors.