Effect of spine neck variation on synaptic plasticity in thin spines. (a) Spatial plots at 15 and 30 ms for thin spines of the same volume with different neck geometries (neck radius of 0.04, 0.06, and 0.07 μm). The number above each spine corresponds to the number of calcium ions present at that time point. Scale bar, 2 μm. (b and c) Calcium ions over time (b) and variance, displayed as variance divided by 1,000 ions (c), for all three thin spines with different neck cases. Shaded regions in b denote SD. (d) Peak calcium ion number for each thin spine with the mean and SEM (n = 50) show no statistically significant differences using a two-tailed t test. We fitted the trend in peak calcium as a linear function of spine neck base surface area; r2 = 0.0009 for the linear fit. (e) We fitted the decay portion of each calcium transient with the exponential decay function c · exp(−kt). The decay time constant mean and SEM (n = 50), k, only statistically significant differences shows between the thin and thick necks; ***, P = 0.0322 from two-tailed t test. We fitted the trend in decay time constants as a function of spine neck base surface area with an exponential a · exp(−bψ), where ψ is the spine neck base surface area; r2 = 0.0256 for the exponential fit. (f) Calculated synaptic weight change at the last time point for all three thin spines shows no statistically significant difference due to neck size.
