Estimates of the mean number of FSIs gap-junction coupled to each FSI, derived from Fukuda's [39] data.

Fukuda reported densities of between 500–4000 gap junctions per across the striatum; we used this to estimate lower and upper bounds for the number of FSIs gap-junction coupled to a FSI, for each FSI density and for between 1 and 3 gap junctions per coupled pair. For example, the first entry of the fourth column indicates that if we assume 2 gap junctions are made per coupled pair and the FSI density is 1%, then each FSI contacts between 0.29 and 2.35 other FSIs via gap junctions. We assumed here a MSN density of 84900 per [35] when computing the density of FSIs.