# Hippocampal sequences represent working memory and implicit timing

## TL;DR

This study shows that the hippocampus uses similar neural sequences to handle both working memory and timing, suggesting these functions are linked.

## Contribution

The paper introduces a novel rodent task combining working memory and timing to reveal shared hippocampal mechanisms.

## Key findings

- Rodents perform worse in working memory tasks when unexpected long delays occur.
- Hippocampal CA1 neurons show odor-specific sequential activity during delays.
- Neural sequences reflect expectations about timing, linking working memory and timing.

## Abstract

Working memory (WM) and timing are considered distinct cognitive functions, yet the neural signatures underlying both can be similar. To address the hypothesis that WM and timing may be multiplexed, we develop a rodent task where 1st odor identity predicts the delay duration. We find that WM performance decreases when delay expectations are violated. Performance is worse for unexpected long delays than for unexpected short delays, suggesting that WM may be tuned to expire in a delay-dependent manner. Calcium imaging of dorsal CA1 neurons reveals odor-specific sequential activity tiling the short and long delays. Neural sequence structure also reflects expectation of the timing of the 2nd odor—i.e., of the expected delay. Consistent with the hypothesis that WM and timing may be multiplexed, our findings suggest that neural sequences in dorsal CA1 may encode cues and cue-specific elapsed time during the delay period of a WM task.

Dorian et al. develop a differential-delayed-non-match-to-sample (dDNMS) task for rodents. Using this olfactory working memory and implicit timing task, they demonstrate that sequential activity in hippocampal CA1 is a shared mechanism for the encoding of working memory and timing.