Table 2.

Size of the active neuronal ensembles under the AA/AA′/AB′/AB protocols

	CA3 (%)	CA2 (%)	CA1 (%)
AA
arc	6.4 ± 0.9ΔΔ	5.3 ± 0.8ΔΔ	13.8 ± 2.0
H1a	9.5 ± 1.3	7.3 ± 0.7###	13.8 ± 1.1
AA′
arc	8.5 ± 0.5ΔΔΔ	4.7 ± 0.8ΔΔΔ	19.9 ± 1.1*
H1a	9.5 ± 0.8	6.3 ± 1.2##	12.0 ± 0.8
AB′
arc	6.6 ± 0.7ΔΔΔ	5.9 ± 1.7ΔΔΔ	23.4 ± 1.7***
H1a	9.7 ± 1.0	5.1 ± 1.0###	13.2 ± 1.7
AB
arc	7.2 ± 0.8ΔΔΔ	11.0 ± 2.0ΔΔΔ	23.6 ± 3.2***
H1a	9.8 ± 0.8	5.6 ± 0.9##	12.1 ± 1.5

*CA1 arc in AA′, AB′, and AB mice is elevated compared to AA mice; *p < 0.05, ***p < 0.001.

^Δarc expression is significantly lower in CA2 and CA3 compared with CA1; ^ΔΔp < 0.01, ^ΔΔΔp < 0.0001.

^#H1a expression is significantly lower in CA2 compared with CA1; ^##p < 0.01, ^###p < 0.0001.

Percentage (mean ± SEM) of neurons scored Arc+ or H1a+ in CA1, CA2, and CA3 of C57BL/6 wild-type mice subject to the AA/AA′/AB′/AB protocols. For Arc expression we found a significant interaction between protocol and subregion with significantly more Arc in the CA1 of AA′, AB′, and AB mice compared with AA mice (two-way ANOVA, F_(1,6): protocol × subregion = 3.44, p = 0.0044; Bonferroni post-test AA × AA′: CA1, p < 0.05; CA2 and CA3, p > 0.05; AA × AB′: CA1, p < 0.0001; CA2 and CA3, p > 0.05; AA × AB: CA1, p < 0.0001; CA2 and CA3, p > 0.05). When we compared Arc expression across subregions within protocols we find that levels in CA2 and CA3 are similar and both are significantly lower than levels in CA1 (Bonferroni post-test CA1 × CA2: AA, p < 0.01; AA′, p < 0.0001; AB′, p < 0.0001; AB, p < 0.001; CA1 × CA3: AA, p < 0.01; AA′, p < 0.0001; AB′, p < 0.0001; AB, p < 0.001) . For H1a expression we found no interaction or protocol effect, but observed a significant effect of subregion (two-way ANOVA, F_(1,6): protocol × subregion = 0.41, p = 0.868; F_(1,3): protocol = 0.56, p = 0.644; F_(1,2): subregion = 36.8, p < 0.0001; Bonferroni post-test CA1 × CA2: AA, p < 0.001; AA′, p < 0.01; AB′, p < 0.0001; AB, p < 0.001), with overall levels significantly lower in CA2 compared with CA1.