A mouse’s brain must decide, in a split second, whether a rustling sound and a flicker of movement come from the same nearby threat—and whether to freeze or flee. The superior colliculus, an ancient brain region found in all vertebrates, fuses sound and sight into a single map of space. Scientists already know how this structure maps left–right and up–down. But they do not understand how it judges *distance*—the third dimension. Because light travels a million times faster than sound, a predator’s roar arrives later than its image, and the brain uses that delay to estimate how far away the source is. This project will record from thousands of neurons in mice as they hear and see simulated threats, then use optogenetics to trace the circuits that turn sensory delay into a decision to freeze or escape. This is fundamental science. It asks how a compact, evolutionarily ancient brain region computes three-dimensional space from mismatched sensory timings. A deeper understanding of these circuits could eventually inform neural prosthetics for people with impaired spatial awareness, or inspire algorithms for robots that must fuse audio and visual data to navigate cluttered environments. But the immediate payoff is a clearer picture of how any brain—mouse or human—builds a coherent world from two very different senses.
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In order to generate appropriate responses to external events, living organisms often need to combine sensory information of multiple modalities. Specific brain areas weigh and combine this information to form a precise representation of the outside world and instigate optimised behavioural outputs. The superior colliculus (SC) is an evolutionary conserved structure, where sensory inputs from multiple modalities are integrated in the same coordinate system to trigger orienting and escape behaviours. The representation of space in the horizontal and vertical axes in the SC has been well characterised, however, the neural bases for judging the third dimension - source distance - are less well understood. The difference between the velocities of light and sound introduces a distance dependent lag for auditory signals with respect to visual information. Visual-auditory neurons in the SC are sensitive to this delay. We will study the multisensory three dimensional representation of space in anatomically defined regions of the SC by performing large-scale neuronal recordings. We will investigate the network mechanisms underlying spatiotemporal multisensory integration using optogenetic and functional circuit tracing approaches. We will then determine how animals combine audio-visual information to estimate the location of a threat and to guide the selection of defensive responses, such as freezing and scape. Finally, we will determine multisensory cellular computations in SC neurons using two-photon calcium and voltage imaging of dendritic spines and their parent dendrites. This multiscale approach will reveal the mechanism underlying the multisensory representation of three dimensional space and how the estimation of threat location is used to guide behavioural responses.
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