Contextual fear conditioning is disrupted by lesions of the subcortical, but not entorhinal, connections to the hippocampus

Recent studies have questioned the importance of the entorhinal cortex (ERC ) for normal hippocampal function. For example, fibre-sparing ERC lesions h ave been found to have no effect on spatial learning in the watermaze. Ther e is also doubt as to the importance of the ERC for contextual fear conditi oning, with previous studies having yielded conflicting results. In an atte mpt to resolve this issue, the present study compared aspiration and cytoto xic ERC lesioned rats, along with fimbria-fornix (FFX) lesioned animals and sham operated controls, on an unsignalled contextual fear conditioning par adigm. The results of the present study show that whereas lesions of the FF X disrupted contextual freezing, neither aspiration nor cytotoxic ERC lesio ns had any effect on this behaviour. Aspiration ERC lesioned rats, however, like FFX lesioned animals, did display hyperactivity prior to the delivery of footshock. These results suggest that whereas projections between the h ippocampus and subcortical structures are important for normal levels of co ntextual freezing, projections from the entorhinal cortex are not essential .