Table 1.

Summary of determined parameters

	Determination	YU	YL	AU	AL	Change with age	Test	P value
								U location	L location
$\overline{{\mathit{w}}_{\mathit{\Sigma }\mathit{\Phi }}}$ (µV⋅%−1⋅µm−2)	Meas.	1.27 ± 0.20	2.15 ± 0.32	2.08 ± 0.43	3.81 ± 0.44	Increase	M-W	0.09	0.006
${\mathit{\Phi }}_{\mathit{max}}$ (%)	Meas.	17.6 ± 1.9	17 ± 1.6	10.1 ± 1.3	9.4 ± 1.1	Decrease	M-W	0.005	0.001
$\overline{{\mathit{w}}_{\mathit{\Sigma }\mathit{\Phi }}}·{\mathit{\Phi }}_{\mathit{max}}$ (µV⋅µm−2)	Meas.	20 ± 2.9	36.4 ± 6.4	22.1 ± 6.5	32.2 ± 3.7		M-W	0.74	0.79
$\mathit{\Delta }{\mathit{z}}_{\mathit{tree}}$ (µm)	Meas.	3.99 ± 0.26	4.11 ± 0.21	3.82 ± 0.11	3.92 ± 0.28		Stu	0.58	0.63
${\mathit{d}}_{\mathit{S}}$ (µm−3)	Meas.	0.73 ± 0.05	0.72 ± 0.03	0.86 ± 0.06	0.73 ± 0.08		Stu	0.13	0.96
$\mathit{\Delta }{\mathit{z}}_{\mathit{tree}}·{\mathit{d}}_{\mathit{S}}$ (µm−2)*	Calc.	3.02
${\mathit{\Phi }}_{1\mathit{PF},\mathit{ in }4\mathit{AP}}$ (%)	Meas.	0.66 ± 0.04	0.52 ± 0.02	0.43 ± 0.02	0.49 ± 0.02	Decrease	M-W	<0.0001	0.17
$\overline{\mathbf{\Sigma }{\mathit{\Phi }}_{1\mathit{PF}}}$ (%⋅µm2)†,‡	Calc.	4.11 ± 1.24	3.20 ± 0.93	2.68 ± 0.81	3.03 ± 0.89
$\mathit{\alpha }·{\mathit{d}}_{\mathit{PF}}$ (µm−2)†,‡	Calc. Eq. 5	4.27 ± 1.77	5.3 ± 2.06	3.77 ± 1.63	3.09 ± 1.27
${\mathit{d}}_{\mathit{PF}}$ (µm−2)	Meas.	7.85	6.8	6.3	5.75
$\mathit{\alpha }$ §	Calc.	0.66		0.57
$\overline{\mathit{w}}$ (µV)	Calc. Eq. 6	10 ± 1.5	18.3 ± 3.2	12.9 ± 3.8	18.8 ± 2.2		M-W	0.94	0.77
$\overline{{\mathit{w}}_{\mathit{t}}}$ (µV)	Meas.	70.6 ± 16.2		85.4 ± 25.9			M-W	0.94
$\mathit{f}$ (%)‡	Calc. Eq. 7	86 ± 5	74 ± 11	85 ± 9	78 ± 9

Determination (measured [Meas.] or calculated [Calc.]), values, change with age, and statistical test (Mann–Whitney U [M-W] or Student’s t [Stu]).

*In vivo areal synapse density per PC, assumed constant based on the similarity of $\mathrm{\Delta }{z}_{\mathit{tree}}$ and $d_S$ values between groups and their low variation coefficient (see main text).

^†Calculated from ${\mathrm{\Phi }}_{1PF, in 4AP}$ (see SI Appendix).

^‡Propagated errors.

^§Calculated $\alpha$ values were 0.54, 0.78, 0.60, and 0.54 for YU, YL, AU, and AL groups, respectively. Since U and L groups were from the same slice preparations, $\alpha$ was averaged between U and L loci.