Audiovisual strategies, regions, and connections in the mouse brain

Combining visual and auditory signals in the environment is central to survival, whether predator, prey, or pedestrian. Despite this ubiquity, studies disagree on how and where auditory and visual information is integrated in the brain. These disagreements are hypothesised to arise from differences in behavioural tasks and animal states (running or stationary). I propose to test this hypothesis and interrogate the underlying neural circuitry with state-the-art optogenetic techniques. First, I will train the same mice on two established behavioural tasks known to produce distinct audiovisual integration strategies: one where auditory and visual information streams are equally combined, and one where a single modality dominates. This will determine whether differences in strategy are attributable to differences in task structure, and whether behavioural state has a consistent impact on these strategies. Second, I will use an established optogenetics technique to reversibly inactivate 52 cortical regions in each mouse as they transition between behavioural tasks and states. This will establish whether the audiovisual circuitry changes with task structure, as has been proposed, and may also uncover new multisensory pathways. Finally, I will use a novel combination of optogenetic tools to causally test connections from all 52 cortical regions to a specific target region in each mouse. This will reveal whether switching between tasks leads to differences in the communication between brain regions and links these to task structure and behavioural state. These results will reveal foundational principles of audiovisual integration and will provide a foothold to understand why failures in this process are associated with cognitive disorders. Furthermore, revealing how differences in task structure can change the behaviour of animals and the underlying neural circuitry will have board implications for studies throughout behavioural neuroscience.