A core aspect of clinical epileptology revolves around relating epileptic field potentials to underlying neural sources (e.g. an “epileptogenic focus”). Yet still, how neural population activity relates to epileptic field potentials, especially across neuroanatomical scales, remains far from being understood. The talk will provide new insights on this topic, based on hippocampal and neocortical chronic in vivo two-photon population imaging and local field potential recordings of epileptic micronetworks in mice, and invasive depth electrode recordings (macroelectrodes and BF microwires) in epilepsy patients during pre-surgical evaluation. References: Wenzel M, Hamm JP, Peterka DS, Yuste R. (2019) Acute focal seizures start as local synchronizations of neuronal ensembles. J Neurosci. 39 (43) 8562-8575, doi: 10.1523/JNEUROSCI.3176-18.2019 Bando Y, Wenzel M, Yuste R. (2021) Simultaneous two-photon imaging of action potentials and subthreshold inputs in vivo. Nat Commun. 12(1):1-12. doi:10.1038/s41467-021-27444-9 Wenzel M, Huberfeld G, Grayden DB, Curtis M De, Trevelyan AJ. (2023) A debate on the neuronal origin of focal seizures. Epilepsia. 00:1-12. doi:10.1111/epi.17650