Extended Data Fig. 4. Validation of core-variable model and contact scoring.

a-c, Core-variable model reliably predicts the empirical synaptic and gap junction contact reproducibility (${\mathbb{C}}^{\delta }$ and ${\mathbb{G}}^{\delta }$) on ${\mathbb{M}}^2$ and ${\mathbb{M}}^3$. To predict synaptic/gap junctional contact counts on ${\mathbb{M}}^{j<\mathit{4}}$ contacts, ${\mathbb{C}}^{\delta }$ (or ${\mathbb{G}}^{\delta }$) contact counts on ${\mathbb{M}}^4$ are scaled by the ratio of all $\mathbb{C}(\mathbb{G})$ on ${\mathbb{M}}^j$ count : all $\mathbb{C}(\mathbb{G})$ on ${\mathbb{M}}^{\mathit{4}}$ count (Methods). E.g. in a, the model predicts a ${\mathbb{C}}^3$ count on ${\mathbb{M}}^3$ contacts as 206×285/1474 = 40 where 206 is the empirical ${\mathbb{C}}^3$ count on ${\mathbb{M}}^4$ contacts, 285 is the total empirical synaptic contact count, $\mathbb{C}$, on ${\mathbb{M}}^3$ and 1474 is the total empirical count of synaptic contacts on ${\mathbb{M}}^4$. The model prediction is consistent with the empirical ${\mathbb{C}}^3$ on ${\mathbb{M}}^3$ count (43). Error bars: $\pm \surd n$, where $n$ is the empirical or predicted count (see Source Data for precise $n$ values). d, Chemical synapses and e, gap junctions also consist of a core and variable circuit. Surrogate model data for ${\mathbb{C}}^{\delta }$ and ${\mathbb{G}}^{\delta }$, generated as in Fig. 2b. Across each dataset, ~62% of synaptic contacts and ~59% of gap junction contacts consist of target contacts (given by $fp/\left[fp+\left(1-f\right)\left(1-s\right)\right]$, Methods). f,g, Core synaptic contacts are typically larger than variable ones in both Cook et al. (2019)³ and White et al. (1986)⁵. Distribution of f, ${\mathbb{C}}^{\delta }$ and g, ${\mathbb{G}}^{\delta }$ contact counts by EM sizes (the total number of EM sections in which a contact was observed)^3,7. To check for biases in contact size due to possible differences in synaptic/gap junction scoring criteria, we compare the distributions of EM sizes for contacts identified by White et al. (1986)⁵ (orange) and those identified by Cook et al. (blue). Because White et al. (1986)⁵ does not provide EM sizes, we used the EM sizes from Cook et al. (2019)³ for all contacts. Although many additional synapses identified by Cook et al. (2019)³ occur only in 1 EM section, we find no systematic bias towards smaller synaptic contacts by Cook et al. (2019)³. h,i, Bidirectional comparison of Cook et al. (2019)³ and Witvliet et al. (2020)²⁰ synaptic contact reproducibility. h, Fraction of Cook et al. (2019)³ synaptic contacts scored by Witvliet et al. (2020)²⁰. i, Fraction of Witvliet et al. (2020)²⁰ synaptic contacts scored by Cook et al. (2019)³. h,i, Fractions of the total empirical count of synaptic contacts $(n)$.