THE DORSAL HIPPOCAMPUS IS ESSENTIAL FOR CONTEXT DISCRIMINATION BUT NOT FOR CONTEXTUAL CONDITIONING

The authors describe how (a) the timing of hippocampal lesions and (b) the behavioral-representational demands of the task affect the requir ement for the hippocampus in contextual fear conditioning. Post- but n ot pretraining lesions of the hippocampus greatly reduced contextual f ear conditioning. In contrast, pretraining lesions of the hippocampus abolished context discrimination, a procedure in which mice are traine d to discriminate between 2 similar chambers (shock context vs. no-sho ck context). Whereas either contextual- or cue-based strategies can be used to recognize an aversive context, discrimination between similar contexts is optimally acquired by contextual (hippocampal)-based stra tegies. In keeping with the lesion results, Nf1(+/-)/Nmdar1(+/-) mutan t mice, which have spatial learning deficits, are impaired in context discrimination but not in contextual conditioning. Together, these dat a dissociate hippocampal and nonhippocampal contributions to contextua l conditioning, and they provide direct evidence that the hippocampus plays an essential role in the processing of contextual stimuli.