Individual quantitative observations that underlie the data summarized in the figures and results of the paper.

In Figs 3 and 4 and S3 Fig, to quantify the confidence intervals in the measured fractions of spine gain, spine loss, spine turnover, Occupancy, and Transitions, we used a 2-level bootstrapping method, which accounts both for heterogeneity between neurons and for heterogeneity between spines within a neuron (“Quantification and statistical analysis” in the Methods section for more details). The procedure was repeated 10,000 times, and the error bars denote the standard deviations of the distribution of these quantities across the different samples. (XLSX)