A two-choice discrimination method to assess olfactory performance in pigtailed macaques, Macaca nemestrina

Abstract

Four pigtailed macaques were trained in a new two-choice olfactory discrimination method. They learned the initial task within 3 months, requiring a maximum of 900 trials. After the method was established, we investigated the olfactory threshold of three monkeys for the odors peanut, iso-amyl acetate, and n-pentanoic acid. The animals detected peanut odor in dilutions as low as 1:10 000. They were able to perceive iso-amyl acetate up to a 30 000-fold dilution (animals F1 and M2), respectively in a 30 Mio-fold dilution (animal M1). The sensitivity for n-pentanoic acid ranged between a dilution of 1:30 000 (F1), 1:100 000 (M2), and 1:300 000 (M1). A comparison with the thresholds of other species demonstrates that the olfactory sensitivity of pigtailed macaques is not necessarily inferior to that of species that are believed to have a very keen sense of smell, such as dogs and rats. The sensitivity for certain odors seems to reflect their biological relevance for the tested species. The fact that the threshold for peanut odor obtained in this study is lower than the one found in a previous study with pigtailed macaques using a multiple olfactory discrimination method indicates that the new two-choice discrimination method is a better candidate for the assessment of olfactory abilities in pigtailed macaques.