Fig. 7.

Differential BD tree dynamics in neonatal barrel cortex SS neurons. a In the normal neonatal mouse barrel cortex, eSS neurons receive spatially biased TCA inputs, predominantly from the barrel-center side (yellow); while on the other side (white), they receive no inputs or inputs from inappropriate TCAs. At P3, eSS neurons already have BD orientation bias, albeit weak, toward the barrel-center side (Fig. 2g). However, at this age, individual BD trees are still primitive (Figs. 2f, 3d and Supplementary Fig. 3b) and the BD orientation bias is ascribed primarily to the larger number of BD trees on the barrel side vs. the other side (Fig. 3c). BD orientation bias increases drastically between P3 and P6 (Fig. 3b), while the ratio of inner tree number to total tree number does not change (Supplementary Fig. 3a). BD trees are highly dynamic and emerge (orange) and disappear (dashed gray BDs) frequently both inside and outside the barrel center-side half (Fig. 4a–e). Meanwhile, only a fraction of trees (mostly inner) are stabilized (Fig. 4d–f) and these become extensively elaborated over time to become “winners” (red) (Fig. 4g). BD trees born later also have a chance to become winners (Supplementary Fig. 3f). b cSS and iSS neurons receive TCA inputs (yellow) from all directions (no biased inputs). In this situation, BD tree turnover is suppressed (Fig. 5g, h), few winners and losers are found, and most trees elaborate moderately (Fig. 5d and Supplementary Fig. 5j)