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.