Spontaneous neuronal activity is spatiotemporally structured, influencing brain computations. Nevertheless, the neuronal interactions underlying these spontaneous activity patterns, and their biological relevance, remain elusive. We addressed these questions using two-photon Ca2+ imaging of intact zebrafish larvae to monitor the spontaneous activity fine-structure in the tectum. The spontaneous activity is organized in topographically compact assemblies, grouping functionally similar neurons rather than merely neighboring ones, reflecting the tectal retinotopic map. Assemblies show attractor-like dynamics, improving visual detection in noisy natural environments. These assemblies also emerged in “naive” tecta (tecta of enucleated larvae before the retina connected to the tectum). We thus suggest that the formation of the tectal network circuitry is genetically prone for its functional role. This capability is an advantageous developmental strategy for the prompt execution of vital behaviors, such as escaping predators or catching prey, without requiring prior visual experience.
Mutant zebrafish larvae for the mecp2 gene display an abnormal spontaneous tectal activity suggesting disrupted functional connectivity. These mutant fish show no attractor circuits and an exagerated visual response, suggesting that the functional connectivity of the optic tectum acts as a virtual top-down fovea, improving spatial resolution.