Changes in odor quality discrimination following recovery from olfactory nerve transection

Following recovery from olfactory nerve transection, animals regain theirability to discriminate between odors. Odor discrimination is restoredafter new neurons establish connections with the olfactory bulb. However,it is not known if the new connections alter odor quality perception. Toaddress this question, 20 adult hamsters were first trained to discriminatebetween cinnamon and strawberry odors. After reaching criterion (> or =90% correct response), half of the animals received a bilateral nervetransection (BTX) and half a surgical sham procedure. Animals were nottested again until day 40, a point in recovery when connections arere-established with the bulb. When BTX animals were tested without foodreinforcement, they could not perform the odor discrimination task. Shamanimals, however, could discriminate, demonstrating that the behavioralresponse had not been extinguished during the 40 day period. Whenreinforcement was resumed, BTX animals were able to discriminate betweencinnamon and strawberry after four test sessions. In addition, theirability to discriminate between these two familiar odors was no differentthan that of BTX and sham animals tested with two novel odors, baby powderand coffee. These findings suggest that, after recovery from nervetransection, there are alterations in sensory perception and thatrestoration of odor quality discrimination requires that the animal mustagain learn to associate individual odor sensations with a behavioralresponse.