# Evidence for Auditory Stimulus‐Specific Adaptation But Not Deviance Detection in Larval Zebrafish Brains

## TL;DR

This study shows that larval zebrafish brains adapt to repeated sounds but do not detect unexpected ones, similar to how humans and other animals do.

## Contribution

The first evidence of stimulus-specific adaptation in larval zebrafish auditory systems is presented.

## Key findings

- Zebrafish brains show frequency-specific adaptation to repeated sounds.
- No deviance detection was observed for unexpected sounds or omissions in sound sequences.
- Whole-brain calcium imaging revealed variable response amplitudes to different sound frequencies.

## Abstract

Animals receive a constant stream of sensory input, and detecting changes in this sensory landscape is critical to their survival. One signature of change detection in humans is the auditory mismatch negativity (MMN), a neural response to unexpected stimuli that deviate from a predictable sequence. This process requires the auditory system to adapt to specific repeated stimuli while remaining sensitive to novel input (stimulus‐specific adaptation [SSA]). MMN was originally described in humans, and equivalent responses have been found in other mammals and birds, but it is not known to what extent this deviance detection circuitry is evolutionarily conserved. Here we present the first evidence for SSA in the brain of a teleost fish, using whole‐brain calcium imaging of larval zebrafish at single‐neuron resolution with selective plane illumination microscopy. We found frequency‐specific responses across the brain with variable response amplitudes for frequencies of the same volume and created a loudness curve to model this effect. We presented an auditory “oddball” stimulus in an otherwise predictable train of pure tone stimuli and did not find a population of neurons with specific responses to deviant tones that were not otherwise explained by SSA. Further, we observed no deviance responses to an unexpected omission of a sound in a repetitive sequence of white noise bursts. These findings extend the known scope of auditory adaptation and deviance responses across the evolutionary tree and lay groundwork for future studies to describe the circuitry underlying auditory adaptation at the level of individual neurons.

The mismatch negativity response is brain activity following an unexpected auditory stimulus in humans. We used whole‐brain calcium imaging to characterize auditory responses to unexpected sounds in larval zebrafish. Auditory neuron responses decrease after repetition of specific frequencies without generalization between frequencies, evidence of stimulus‐specific adaptation. However, we did not find evidence for deviance responses to unexpected sounds within a sequence or to the unexpected omission of sounds from a sequence.