Spike inference from calcium imaging data acquired with GCaMP8 indicators

Calcium imaging is a central method in neuroscience but it records neuronal activity only indirectly and thereby produces results that are difficult to interpret. Here we evaluate the GCaMP8 calcium indicator variants, together with methods to infer neuronal spiking, and thus interpret GCaMP8 recordings. We find that the linearity of GCaMP8 indicators enables accurate detection of both single action potentials and high-frequency spiking events. Ground-truth recordings from mouse neocortex show that the most linear variants GCaMP8s and GCaMP8m (but not GCaMP6, GCaMP7f or GCaMP8f) robustly detect isolated spikes in cortical pyramidal neurons. In addition, we fine-tune and benchmark algorithms for spike inference (CASCADE, OASIS and MLSpike) with data from all GCaMP8 variants for pyramidal neurons and interneurons, and we demonstrate how the fast rise time of GCaMP8 indicators enables real-time detection of neuronal activity. Overall, we provide tools and guidelines to optimally process GCaMP8 calcium signals and highlight the key role of linearity in interpreting calcium imaging data.