Hippocampal sequences represent working memory and implicit timing

Area of Science:

• Neuroscience
• Cognitive Science
• Animal Behavior

Background:

• Working memory (WM) and timing are typically viewed as separate cognitive processes.
• However, overlapping neural mechanisms suggest potential integration or multiplexing.
• Understanding this relationship is key to deciphering complex cognitive functions.

Purpose of the Study:

• To investigate the hypothesis that working memory and timing are multiplexed in the brain.
• To explore how neural activity encodes temporal expectations within a working memory task.
• To determine if dorsal CA1 neural sequences reflect both cue identity and elapsed time.

Main Methods:

• Developed a rodent task where the identity of the first odor predicts the delay duration.
• Assessed working memory performance based on violated delay expectations.
• Utilized calcium imaging of dorsal CA1 neurons to record neural activity during the task.

Main Results:

• Working memory performance declined when delay duration expectations were violated.
• Performance was more impaired by unexpected long delays than short delays.
• Odor-specific sequential neural activity in dorsal CA1 tiled both short and long delays.
• Neural sequence structure reflected the expected timing of the second odor (delay duration).

Conclusions:

• Findings support the hypothesis that working memory and timing are multiplexed.
• Neural sequences in dorsal CA1 encode cues and cue-specific elapsed time during working memory delays.
• This suggests a unified neural mechanism for processing temporal information within working memory tasks.