Voltage imaging reveals that hippocampal interneurons tune memory-encoding pyramidal sequences.

Area of Science:

• Neuroscience
• Computational Neuroscience

Background:

• Hippocampal spiking sequences are vital for encoding behavioral information across time.
• The precise role of neural inhibition in sculpting these sequences remains largely unexplored.

Purpose of the Study:

• To investigate how parvalbumin and somatostatin interneurons shape hippocampal activity during an odor-cued working memory task.
• To understand the temporal dynamics of inhibition and its impact on cue representation before and after task training.

Main Methods:

• Longitudinal voltage imaging of CA1 parvalbumin- and somatostatin-expressing interneurons in mice.
• Utilized an odor-cued working memory task, with imaging performed pre- and post-training.
• Two-photon calcium imaging was employed to assess pyramidal cell activity.

Main Results:

• Pyramidal cells formed odor-specific sequences encoding cues during the delay period.
• Interneurons predominantly responded to odor delivery, not identity or delay time.
• Population inhibition remained stable, but individual cells showed odor-responses; pyramidal cells were suppressed by odor onset, with positive responses coinciding with interneuron rebound spiking.

Conclusions:

• Neural inhibition enhances the signal-to-noise ratio of cue representations in the hippocampus.
• This enhanced representation is critical for entraining downstream neural targets during memory tasks.
• Interneuron activity dynamics, including rebound spiking, play a key role in modulating pyramidal cell responses.