In-flight brainstem responses highlight the encoding of self-emitted echolocation calls in bats

Echolocating bats rely on precise auditory processing to navigate and forage in complete darkness. A critical aspect of this behaviour is the neural encoding of self-generated vocalizations, which allows for accurate comparison with returning echoes. In this study, we introduce a non-invasive method for recording auditory brainstem responses (ABRs) in awake, flying big brown bats (Eptesicus fuscus). Using a custom 3D-printed harness that enables sustained in-place flight, we simultaneously recorded electroencephalographic and acoustic signals from freely vocalizing animals. Self-emitted echolocation calls reliably evoked ABRs, including a distinct pre-auditory wave that occurred before call onset and is probably associated with motor command generation. We were able to extract single-trial individual ABR patterns, which revealed significant correlations between specific acoustic properties of the calls and both ABR amplitude and latency. These findings demonstrate that, despite the suggested peripheral attenuation of self-emitted echolocation calls, the bat auditory system dynamically encodes the characteristics of outgoing vocalizations, with information extraction occurring as early as the brainstem. Our approach offers an effective framework for investigating sensory-motor integration in actively behaving animals.