DIFFERENTIAL CONTRIBUTIONS OF INTERNEURON SUBTYPES TO HIPPOCAMPAL VALUE PROCESSING

Accumulating evidence indicates that value representation constitutes an integral component of hippocampal mnemonic processing. However, how value-related signals are organized and transformed within hippocampal microcircuits remains largely unknown. To address this issue, we employed one-photon calcium imaging to monitor the activity of parvalbumin (PV)-, somatostatin (SST)-, and vasoactive intestinal peptide (VIP)-expressing interneurons in the dorsal CA1 region while mice performed a probabilistic classical conditioning task. In this task, three odor cues predicted water reward delivery with probabilities of 75%, 25%, or 0%. All three interneuron subtypes exhibited robust value-related activity, but with distinct temporal dynamics and quantitative profiles. SST interneurons exhibited rapidly emerging cue-evoked value signals and stronger outcome-related value responses compared to other subtypes. In contrast, PV interneurons showed value-related activity that persisted across successive trials, suggesting a role in maintaining value information over time. During the outcome period, interneuron activity across all subtypes was suppressed by reward delivery itself, yet scaled with expected value, consistent with a role in computing reward prediction error. These findings suggest that distinct CA1 interneuron subtypes make dissociable contributions to hippocampal value computations. Ongoing work is examining how subtype-specific manipulations of interneurons influence pyramidal cell value representations and behavioral performance.