Nonlinear super-resolution signal processing for subcellular analysis of calcium dynamics

Abstract Fluorescence imaging of calcium dynamics has revolutionized cellular biology, and especially neuroscience as it allows the study of neural activity across spatially well defined populations. Quantification of fluorescence signals is commonly performed using ratiometric measures. These measures, such as ΔF/F, are easy to implement, but they depend on the definition of a baseline, which is often not trivial outside of the measurement of evoked responses, and needs to be defined for every cell (or other cellular compartment) separately. Here, we present a new quantitative measure of fluorescence by taking advantage of the time dimension of the signal. The new method, which we named ARES (Autoregressive RESiduals), is based on the quantification of residuals after linear autoregression and does not require arbitrary baseline assignment. We detail the basic characteristics of the ARES signal, compare it against ΔF/F, and quantify the improvement in spatial and temporal resolution of recorded calcium data. We further exemplify its utility in the study of intracellular calcium dynamics by describing the propagation of a calcium wave inside a dendrite. As a robust and accurate method for quantifying fluorescence signals, ARES is particularly well-suited for the study of spontaneous as well as evoked calcium dynamics, subcellular localization of calcium signals, and spatiotemporal tracking of calcium dynamics. Highlights A baseline-free quantitative measure of fluorescence is introduced The method, called ARES, is based on autoregression ARES improves the spatiotemporal resolution of calcium imaging recordings Its utility for the localization and spatiotemporal tracking of calcium is shown