Table 3.

Summary of the models used.

type of network	coupling	method of generation	key results
homogeneous lattice	symmetrical	fixed coupling κ	minimum and maximum coupling for each perturbation in which global excitation is possible
Bernoulli lattice	symmetrical	fixed coupling κ with varying probability p	even when global excitation cannot occur in the fully connected lattice, it can be attained in a partially connected system
uniformly distributed	symmetrical	couplings drawn from a uniform distribution on [0.5,10] with varying probability p	total coupling between neighbouring cells has a minimum and maximum threshold for global excitation. Between these values (and with constant total coupling), the ability to achieve global excitation is dependent on the standard deviation of coupling values
cell capacitance	asymmetrical	coupling κ = RC−1. C is drawn from distribution of cell capacitance taken from experimental data. R is fixed. Probability p is varied	the presence of spatial heterogeneity is essential for global excitation at comparable perturbation values to the Bernoulli lattice. A larger perturbation is needed for full excitation and full connectivity. There is no discernible difference between day 15 and day 18 gestation
resting membrane potential	symmetrical	fixed coupling κ. Each cell has its own parameters and so its own resting membrane potential	increase in gestational age results in a smaller excitation threshold for each cell to overcome. Systems with resting membrane potential variation only fail to achieve global excitation
cell capacitance and resting membrane potential combined	asymmetrical	each cell has its own resting membrane potential. C is drawn from distribution of cell capacitance. R is fixed	both forms of variation allow global excitation in heterogeneous systems. A larger perturbation is needed than in the Bernoulli lattice to achieve global excitation at full connectivity
pacemaker cells	symmetrical	central cell is a pacemaker. All other cells as before. Fixed coupling κ with varying probability p	highly connected systems have a greater probability of the pacemaker cell ceasing to be active. The frequency of oscillation of the pacemaker cell decreases with increasing connectivity. At high coupling strength values, connectivity has no effect on the frequency—the only way for a pacemaker to retain a finite frequency is to be isolated