Crossing the scales: Single-neuron recruitment and continuous cortical propagation of slow wave events revealed by integrative opto-magnetic imaging

Population up-states, also referred to as slow wave events (SWEs), are a hallmark of the slow wave brain state in mammalian cortex, typically occurring during deep sleep or under certain types of anesthesia. We explore the neuronal recruitment and propagation of SWEs on observational scales ranging from single neurons to the entire cortex, intertwining optical and translationally relevant functional MRI (fMRI). By two-photon calcium imaging in mouse visual cortex, we demonstrate that all active cells of the observed local micronetwork participate in a population wide SWE. Implementing an optomagnetic-integration concept, involving simultaneous fiber photometry with fast cortical line-scanning fMRI in rats, we identify and follow propagating SWEs across the cortex. We can demonstrate continuous cortical propagation of a SWE by non-invasive line-scanning fMRI. This opens the door for monitoring the spatiotemporal dynamics of a neurophysiological-defined signal - here SWEs. Non-invasive monitoring of SWE propagation might represent a proxy for the functional integrity of local and global cortical networks in rodents and humans.