Multisensory integration enhances audiovisual responses in the Mauthner cell

Multisensory integration combines information from multiple sensory modalities to create a coherent perception of the world. In contexts where sensory information is limited or equivocal, it also allows animals to integrate individually ambiguous stimuli into a clearer or more accurate percept and, thus, react with a more adaptive behavioral response. Although responses to multisensory stimuli have been described at the neuronal and behavioral levels, a causal or direct link between these two is still missing. In this study, we studied the integration of audiovisual inputs in the Mauthner cell, a command neuron necessary and sufficient to trigger a stereotypical escape response in fish. We performed intracellular recordings in adult goldfish while presenting a diverse range of stimuli to determine which stimulus properties affect their integration. Our results show that stimulus modality, intensity, temporal structure, and interstimulus delay affect input summation. Mechanistically, we found that the distinct decay dynamics of feedforward inhibition triggered by auditory and visual stimuli can account for certain aspects of input integration. Altogether, this is a rare example of the characterization of multisensory integration in a cell with clear behavioral relevance, providing both phenomenological and mechanistic insights into how multisensory integration depends on stimulus properties. SIGNIFICANCE STATEMENT Animals integrate multiple sources of information in order to form a percept of the world that allows adaptive behavioral decisions. The current study demonstrates the cellular mechanism that underlies hall-mark features of multimodal integration in individual reticulospinal neurons. Since the Mauthner cells initiate the startle escape response, this characterization emphasizes the role of single neurons in multimodal decision-making. Elucidating the principles and mechanisms by which different senses interact might prove useful in designing or optimizing the sensory environment of people performing perceptually demanding tasks, including individuals with sensory disabilities. ### Competing Interest Statement The authors have declared no competing interest.