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

Population up states or slow wave events (SWEs) represent the main feature of slow wave brain state in mammalian cortex, occurring during deep sleep or under certain types of anesthesia. We explore the neuronal recruitment and propagation of SWE 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 micro network participate in a population wide slow wave. Implementing an optomagnetic-integration concept, involving simultaneous fiber photometry with fast cortical line-scanning fMRI in rats, we identify and follow propagating SWE across the cortex. We can demonstrate continuous cortical propagation of a slow wave event, by non-invasive line-scanning fMRI. This opens the door for monitoring the spatiotemporal dynamics of a neurophysiological-defined signal - here SWE. Non-invasive monitoring of slow wave event propagation might represent a proxy for the functional integrity of local and global cortical networks in rodents and humans.