Performance of mice in discrimination of liquor odors: behavioral evidence for olfactory attention.

We examined performance of mice in discrimination of liquor odors by Y-maze behavioral assays. Thirsty mice were initially trained to choose the odor of a red wine in the Y-maze. After successful training (>70% concordance for each trained mouse), the individual mice were able to discriminate the learned red wine from other liquors, including white wine, rosé wine, sake, and plum liqueur. However, when the mice were tested to distinguish fine differences between 2 brands of red wine, their performance significantly varied among the individual trained mice. Among 10 mice tested, 2 mice were able to discriminate between the red wines (>75% concordance) whereas 6 mice failed to distinguish between them (50-67% concordance, where chance could be assumed to be 50%). More importantly, 2 other mice exhibited lower than 30% concordance, indicating that they were more attracted to the nonrewarded red wine compared with the learned one. This result suggested that the individual mice directed attention to different subsets of volatile components emanating from the rewarded red wine, when they were trained to choose the liquor odor in the Y-maze. Selective attention of mice was also observed in Y-maze behavioral assays using the mixtures of 3 or less pure odorants. Additionally, we also observed that the olfactory attention of mice could be modified through their learning experiences.