Effects of lesions to the hippocampus on contextual fear: Evidence for a disruption of freezing and avoidance behavior but not context conditioning

The effects of ibotenic lesions of the hippocampus on conditioning to conte xtual cues during classical fear conditioning in rats were evaluated by (a) the amount of freezing elicited by contextual cues and (b) the relative av oidance of a shock compartment. In Experiment 1, lesions to the hippocampus had no effect on contextual freezing and marginally affected avoidance aft er repeated sessions. Experiment 2 showed that lesions to the hippocampus d isrupted avoidance when tested after a single conditioning session, while l eaving unaffected the acquisition of contextual freezing. Experiment 3 indi cated 1:hat these lesions decreased the acquisition of contextual freezing when higher footshock intensity was used but had no effect on avoidance aft er repeated conditioning sessions. These results show that freezing and avo idance do not quantify context conditioning similarly. They further indicat e that lesions to the hippocampus may disrupt the expression of these behav iors used as measures of context conditioning but not the acquisition of co ntext conditioning per se.