The critical period for synaptic plasticity. A, EPSPs in perforated patch recordings from GCs at each age were normalized during a 10 min baseline before TBS and binned into 1 min intervals. Insets show example EPSPs before and after TBS. Dotted lines mark baseline. B, Comparison of EPSPs at 25–30 min post-TBS. 4w, n = 7; 6w, n = 5; 8w, n = 5; M, n = 9; one-way ANOVA; F_(3,23) = 26, p < 0.0001; Tukey's post hoc with 4w versus M p < 0.0001, 4w versus 8w p = 0.0002, 6w versus 8w and M p < 0.0001. C, PPRs normalized and binned. Inset shows example EPSPs from a 6w abGC. D, Current injections used to monitor rheobase before and after TBS from a 4w (blue, 20 and 30 pA) and mature GC (black, 50 and 60 pA). TBS did not alter rheobase (2-way ANOVA; F_(1,22) = 0.01, p = 0.9), but rheobase was higher in mature GCs compared with abGCs (F_(3,22) = 14, p < 0.0001; Tukey's post hoc with 4w versus M p = 0.0001, 6w versus M p = 0.0002, 8w versus M 0.004, and no interaction effect (F_(3,22) = 0.61, p = 0.6). 4w, n = 7; 6w, n = 5; 8w, n = 4; M, n = 9.