Neural responses of the auditory midbrain to naturalistic echolocation sequences in Hipposideros armiger

Abstract

The functional properties of the auditory midbrain, inferior colliculus (IC), plays a critical role in James Simmons’s SCAT model of target ranging by echolocation. This SCAT model is based solely on the big brown bat producing frequency-modulated (FM) sonar calls. By contrast, there has been very limited knowledge on how the auditory midbrain may encode target ranging information in bats that produce constant-frequency (CF) sonar calls. Here, we conducted single-unit recordings from the auditory midbrain of passively listening Hipposideros armiger using naturalistic echolocation sequences. We created echolocation sequences from recordings taken from individual bats swung on a moving pendulum that evokes Doppler shift compensation (DSC) of their sonar vocalizations. Our preliminary data revealed a population of IC neurons selectively responded to DSC information in the sequences. To our surprise, we did not find neurons that encode echo delays. Considering published data on FM bats, these results suggest that the functional role of auditory midbrain for echolocation may be distinct between FM bats and CF-FM bats.