The ability to smell remains intact, but does not recover, after olfactory bulb lesions

We examined two unresolved issues regarding the influence of olfactory bulb lesions on the ability to smell. First, we asked whether the sense of smell remains intact or recovers after incomplete and complete removal of both olfactory bulbs and second, whether the qualitative perception of smell changes after lesion. Rats were trained to perform a four-choice olfactory discrimination task and were subsequently prepared with either medium, large, or complete bilateral olfactory bulb lesions. They were retested after a recovery period of either 6 or 22 weeks. The lesion effect depended on lesion size, and not on recovery interval. Animals with complete lesions showed no retention, and a failure to relearn, regardless of the recovery interval. Animals with incomplete lesions showed virtually perfect retention. These results, therefore, indicate first that the sense of smell remains intact following extensive olfactory bulb lesions, and that a previously acquired discrimination is permanently lost after complete olfactory bulb lesions.