Broad frequency sensitivity and complex neural coding in the larval zebrafish auditory system

Most animals have complex auditory systems that identify salient features of the acoustic landscape to direct appropriate responses. In fish, these features include the volume, frequency, complexity, and temporal structure of acoustic stimuli transmitted through water. Larval fish have simple brains compared to adults but swim freely and depend on sophisticated sensory processing for survival.1–5 Zebrafish larvae, an important model for studying brain-wide neural networks, have thus far been found to possess a rudimentary auditory system, sensitive to a narrow range of frequencies and without evident sensitivity to acoustic features that are salient and ethologically important to adult fish.6,7 Here, we have combined a novel method for delivering water-borne sounds, a diverse assembly of acoustic stimuli, and whole-brain calcium imaging to describe the responses of individual auditory-responsive neurons across the brains of zebrafish larvae. Our results reveal responses to frequencies ranging from 100 Hz to 4 kHz, with evidence of frequency discrimination from 100 Hz to 2.5 kHz. Frequency-selective neurons are located in numerous regions of the brain, and neurons responsive to the same frequency are spatially grouped in some regions. Using functional clustering, we identified categories of neurons that are selective for a single pure-tone frequency, white noise, the sharp onset of acoustic stimuli, and stimuli involving a gradual crescendo. These results suggest a more nuanced auditory system than has previously been described in larval fish and provide insights into how a young animal’s auditory system can both function acutely and serve as the scaffold for a more complex adult system. [Display omitted] •Larval zebrafish have neural responses to auditory stimuli up to 4 kHz•Different frequencies elicit distinct responses for frequencies below 2.5 kHz•Responses distinguish pure versus complex stimuli and gradual versus sharp onset•Frequency-selective neurons are organized spatially but are not clearly tonotopic Larval fish are thought to have rudimentary auditory systems sensitive to low frequency. Using calcium imaging, Poulsen et al. show neural responses in zebrafish larvae up to 4 kHz, frequency discrimination up to 2.5 kHz, and unique signatures for simple and complex sounds. The particular responses are located in specific locations across the brain.