Natural acoustic stimuli evoke selective responses in the hippocampus of passive listening bats.

A growing body of research details spatial representation in bat hippocampus, and experiments have yet to explore hippocampal neuron responses to sonar signals in animals that rely on echolocation for spatial navigation. To bridge this gap, we investigated bat hippocampal responses to natural echolocation sounds in a non-spatial context. In this experiment, we recorded from CA1 of the hippocampus of three awake bats that listened passively to single echolocation calls, call-echo pairs, or natural echolocation sequences. Our data analysis identified a subset of neurons showing response selectivity to the duration of single echolocation calls. However, the sampled population of CA1 neurons did not respond selectively to call-echo delay, a stimulus dimension posited to simulate target distance in recordings from auditory brain regions of bats. A population analysis revealed ensemble coding of call duration and sequence identity. These findings open the door to many new investigations of auditory coding in the mammalian hippocampus.