Fig. 1.

Generation of surrogate calcium imaging data. a On the left, points were drawn from a two-dimensional normal distribution, and a neuron was considered part of the assembly when at least one point fell within distance \(\frac {1}{2}\) of its corresponding lattice point at its centre. The contour lines around the mean indicate regions of probability mass 50%, 90%, 99%, and 99.9%. The corresponding assembly is shown on the right. b An example of 10 assemblies (colour coded) embedded in a neural array of 469 neurons. Annuli represent neurons which overlap between two assemblies. c An example of the firing rates for 19 neurons over the course of 120 s. Neurons within the same assemblies simultaneously elevated their firing rates (here at 60 s, 77.5 s and 92 s). d The spike counts for the neurons over the course of 120 s as determined from independent Poisson random variables based on the firing rates shown in c. e The spiking events of a single neuron in a time-window of 10 s (top) and the corresponding calcium fluorescence after convolution with an exponential kernel (bottom). f The calcium fluorescence for the neurons over the course of 120 s. g The deflection of calcium fluorescence from baseline level, \(\frac {\Delta F}{F}\), for the neurons over the course of 120 s. This was the signal from which the algorithms attempted to reconstruct assembly structure