Organizing principles of whole-brain functional connectivity in zebrafish larvae

Network science has begun to reveal the fundamental principles by which large-scale brain networks are organized, including geometric constraints, a balance between segregative and integrative features, and flexible brain areas. However, it remains unknown whether whole-brain networks imaged at the cellular level are organized according to similar principles. Here, we analyze whole-brain functional networks reconstructed from calcium imaging data recorded in larval zebrafish. Our analyses reveal that functional connections are distance-dependent and that networks exhibit hierarchical modular structure and hubs that span module boundaries. We go on to show that spon-taneous network structure places constraints on stimulus-evoked reconfigurations of connections and that networks are highly consistent across individuals. Our analyses reveal, for the first time, basic organizing principles of whole-brain functional brain networks at the microscale. Our overarching methodological framework provides a blueprint for studying the correlated activity at the cellular level using a low-dimensional network representation. Our work forms a conceptual bridge between macro- and microscale network neuroscience and opens myriad paths for future studies to investigate network structure of nervous systems at the cellular level.