FIGURE 6.
(A) Timeline of infusions and mnemonic discrimination tests administered in Experiment 2. Rats were randomly assigned after surgery to either receive vehicle infusions in the first test block (veh-first group; n = 9) or muscimol infusions in the first test block (mus-first group; n = 8). Each test block comprised 3 tests with the same infusion condition. In block 1, veh-first rats received vehicle and mus-first rats received muscimol prior to tests 1–3. In block 2, infusion conditions reversed; veh-first rats received muscimol and mus-first rats received vehicle prior to tests 4–6. (B–E) Performance (% correct trials) on mnemonic discrimination tests in Experiment 2 plotted by trial type, with objects sharing 0, 50, 70, or 90% target-lure overlap. Test performance on days with vehicle infusions (veh) designated by open circles, and on days with muscimol infusions (mus) by filled circles. Data for block 1 are shown in (B,C). Data for block 2 are shown in (D,E). (B,D) Mean ± SEM performance on mnemonic discrimination tests collapsed across blocks 1 and 2, with a total of 30 trials per lure object for each infusion group. As in Experiment 1, performance decreased as target-lure overlap increased [main effect lure: F(3,45) = 61.8, p < 0.001]. Muscimol impaired discrimination across all lures in block 1 (B), but did not impair discrimination in block 2 (D) [main effect block: F(1,15) = 41.2, p < 0.001; block × group: F(1,15) = 116.3, p < 0.001]. (C) Mean ± SEM performance plotted for each test of block 1 (tests 1–3; 10 trials/lure object/infusion group). Muscimol infusions impaired discrimination across all tests of block 1, when lures were relatively novel [main effect group: F(1,16) = 27.2, p < 0.001]; however, rats in the mus-first group showed selective improvement across tests on trials with the more distinct lure objects [main effect test: F(2,32) = 11.2, p < 0.001; test × lure: F(6,96) = 6.13, p < 0.001; 3-way interaction: F(6,96) = 2.86, p < 0.013]. (E) Mean ± SEM performance plotted for each test of block 2 (tests 4–6; 10 trials/lure object/infusion group). Muscimol infusions did not impair discrimination across tests of block 2, when rats of the veh-first group had gained prior experience with lure objects [main effect lure: F(3,45) = 58.5, p < 0.001; all other effects: p’s > 0.11].