Hippocampal sequences represent working memory and implicit timing

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 1^st 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 2^nd 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.