(A) Average post-CS-related single-unit firing during early extinction. (B) Peri-event histogram of CS-related single-unit firing during early extinction (first 100 msec, inset). (C) Average post-CS-related single-unit firing during late extinction. (D) Peri-event histogram of CS-related single-unit firing during late extinction (first 100 msec, inset). (E) Higher average post-CS-related single-unit firing during extinction retrieval in S1 mice, relative to B6 mice, and higher firing during retrieval than late extinction in S1 mice. (F) Peri-event histogram of CS-related single-unit firing during extinction retrieval (first 100 msec, inset). n=6–7 mice per strain, n=55–65 units per test phase and strain. Data are Means ± SEM. * P<.05 versus B6/same task-phase, † P<.05 retrieval versus late extinction.