Fig. 4: Discriminative contextual fear learning induced synaptic strengthening in the vCA1 inputs that convey threat-predictive contextual information to the BA.

a Experimental setup for recording synaptic responses in the Context A vCA1–BA pathway in b–f. ChR2 was expressed in vCA1 neurons active in Context A. Photostimulation selectively activated Context A vCA1 inputs and induced postsynaptic responses in BA neurons (Rec). b Mice were exposed to Context A for labeling vCA1 neurons active in Contest A as in Fig. 3h. Mice in the fear conditioning (FC) group were trained for discriminative fear in Context A on Days 1–5 as in Supplementary Fig. 1b. Mice in the no shock (NS) control group were exposed to the contexts without a shock. c Freezing behavior in Contexts (Ctx) A and B on Day 5 in the FC (11 mice) and NS groups (10 mice). d Traces of EPSCs induced by blue light (1 ms pulses, blue bars), which activated ChR2-expressing Context A vCA1 inputs. EPSCs were recorded at −80 mV, 0 mV, and +40 mV in voltage-clamp mode in the same BA neurons. AMPAR EPSCs were quantified as the peak amplitude of EPSCs recorded at −80 mV (open circles). NMDAR EPSCs were quantified as the average amplitude of EPSC recorded at +40 mV from 47.5 ms to 52.5 ms after photostimulation onset (gray vertical lines and closed circles). SR-95531 (10 μM) was added to block inhibitory postsynaptic currents. e Comparison of the AMPA/NMDA ratio in Context A-specific vCA1–BA pathway between the FC and NS groups (p = 0.024). Two-sided Kruskal Wallis multiple comparisons were used to analyze combined data in e and k. Open circles indicate the AMPA/NMDA ratio in each neuron. Numbers within the bars are the number of neurons examined in each group. f Histogram showing the distribution of the AMPA/NMDA EPSC ratio in Context A inputs to each BA neuron in the FC (red bars, 52 cells) and NS groups (open bars, 37 cells). A dotted vertical line indicates the mean + 2 standard deviations of the AMPA/NMDA ratio in the NS group. g Experimental setup for recording synaptic responses in the Context B vCA1–BA pathway in h–l. ChR2 was expressed in vCA1 neurons active in Context B. Photostimulation activated Context B vCA1 inputs and induced postsynaptic responses in BA neurons. h Mice were exposed to Context B for labeling vCA1 neurons. Mice in the FC group were trained for discriminative fear in Context A on Days 1–5 as in Supplementary Fig. 1b, whereas mice in NS group were exposed to the contexts without a shock. i Freezing behavior in Contexts A and B on Day 5 in the FC (6 mice) and NS groups (8 mice). In the FC group, only discriminators (D, freezing score in Context B on Day 5 <35%) were included in the analysis in j–k. j Left: traces of EPSCs recorded in the Context B pathway. AMPAR and NMDAR EPSCs were induced and recorded as in d. k Comparison of the AMPA/NMDA ratio in Context B vCA1–BA pathway between the FC and NS groups (n.s., not significant; p = 0.68, two-sided Kruskal Wallis multiple comparisons). l Correlation between the average AMPA/NMDA ratio vs. freezing score in Context B on Day 5 (Pearson correlation coefficient r = 0.71, left) and discrimination index [DI = (Context A freezing − Context B freezing)/(Context A freezing + Context B freezing); Pearson correlation coefficient r = 0.69; right]. Both discriminators (D) and generalizers (G, freezing score in Context B on Day 5 >35%) in the FC group were included. For each mouse, the AMPA/NMDA ratios in 4–5 BA neurons were averaged. Error bars represent the SEM. Source data are provided as a Source Data file. See also Supplementary Figs. 8–11.