Extended Data Figure 7. Distribution of log₁₀-transformed normalized projection volumes from the entire matrix presented in Fig. 3.

The values (left-hand y axis, black bars) were number of target regions and derived from Supplementary Table 2. The entire range of the normalized projection volumes in this matrix was between log₁₀ = −14 and log₁₀ = 1.5, and it peaked between log₁₀ = −3.5 and log₁₀ = −3.0. A manual analysis of true positive and true negative signals from 20 randomly chosen injection experiments, representing the range of injection sizes, was used to estimate the false positive rate at different threshold levels, shown on the right-hand y axis (grey circles). True positive values predominantly fall within the range of log₁₀ = −4 to 1.5. For example, at a threshold of log₁₀ = −4, the false positive rate was 27%, dropping to 14.5% at log₁₀ = −3.5. False positives were almost exclusively due to small segmentation artefacts in areas without actual fluorescently labelled axon fibres.