Fig 1. Characteristic features of a calcium imaging movie.

(A) Cell overlap in the spatial domain. Calcium fluorescence observed at pixels W and X contained in the same neuron shows similar behavior, which differs from the calcium fluorescence observed at pixel Y contained in another neuron. The calcium fluorescence observed at pixel Z is the sum of these series when pixel Z is contained by both neurons. (B) Calcium fluorescence overlap in the temporal domain. Calcium fluorescence observed at each pixel is the convolution of calcium ion dynamics into a spike train. If two spikes occur in a short time relative to the time constant of these dynamics, increases in calcium ion concentration due to these spikes will overlap each other.