Role of the hippocampus in contextual memory after classical aversive conditioning in pigeons (C-livia)

We investigated the effects of hippocampal lesions with ibotenic acid (IBO) on the memory of the sound-context-shock association during reexposure to the conditioning context. Twenty-nine adult pigeons were assigned to a non- lesioned control group (CG, N = 7), a sham-lesioned group (SG, N = 7), a hi ppocampus-lesioned experimental group (EG, N = 7), and to an unpaired nonle sioned group (tone-alone exposure) (NG, N = 8). All pigeons were submitted to a 20-min session in the conditioning chamber with three associations of sound (1000 Hz, 85 dB, 1 s) and shock (10 mA, 1 s). Experimental and sham l esions were performed 24 h later (EG and SG) when EG birds received three b ilateral injections (anteroposterior (A), 4.5, 5.25 and 7.0) of IBO (1 mu l and 1 mu g/mu l) and SG received one bilateral injection (A, 5.25) of PBS. The animals were reexposed to the training context 5 days after the lesion . Behavior was videotaped for 20 min and analyzed at 30-s intervals. A sign ificantly higher percent rating of immobility was observed for CG (median, 95.1; range, 79.2 to 100.0) and SG (median, 90.0; range, 69.6 to 95.0) comp ared to EG (median, 11.62; range, 3.83 to 50.1) and NG (median, 7.33; range , 6.2 to 28.1) (P<0.001) in the training context. These results suggest imp airment of contextual fear in birds who received lesions one day after cond itioning and a role for the hippocampus in the modulation of emotional aver sive memories in pigeons.