Exposure to the novel but not familiar OF enhances extinction LTM and reduces reinstatement. a, Experimental time line. To familiarize the rats with the OF, they were allowed to freely explore the apparatus for 30 min 1 d before extinction (Ext). The OF was presented again 1 h before or after extinction. Extinction LTM and reinstatement were then tested (n = 8–9 per group). b, Exposure to the novel (Nov) or familiar (Fam) OF did not affect extinction acquisition. c, Neither pre-extinction nor post-extinction exploration of the familiar OF affected extinction LTM 2 and 7 d after extinction. d, Exposure to the familiar OF had no effect on fear reinstatement. e, OF exploration did not alter locomotor activity in a 5 min test. In the elevated plus maze, rats that explored the OF exhibited no differences from control rats in the number of entries into the open or closed arms (f) or time spent in the open arms (g). Data are expressed as mean ± SEM; *p < 0.05. CFC, contextual fear conditioning.