PLACE AND REWARD CODING OF A REMOTE AUDITORY SIGNAL IN THE HIPPOCAMPUS

Hippocampus in mammals is hypothesized to support the formation of episodic memory. It may arise out of the convergence of multimodal inputs at the hippocampus. To understand how this structure contributes to the process, we tested its response in a sound–location–reward association task. We investigated whether hippocampal activity accounts for information related to the location of a remote auditory signal and its association with rewards. To test this, we concurrently recorded extracellular electrophysiological activity from the dentate gyrus, CA3, and CA1 regions along the dorso–ventral axis of the hippocampus, together with facial behaviour in five mice, chronically implanted with Neuropixels 1.0 and 2.0 probes. During the experiment, we subjected head-fixed mice to a moving speaker in experimentally defined trajectories, playing pulses of sound at 12-14 Hz, with each pulse containing white noise sampled at an ultrasonic sampling rate (>40 kHz). Here we report evidence for a heterogenous code, inferred from ~700 single units, across 5 mice, comprising of ~20% units specifically related to reward epochs and around 1% of units coding for the proximity to the animal. At the population level, decoding of population activity revealed regimes consistent with active tracking of the sound source. These results suggest a unified hippocampal role in binding different dimensions of experience.