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

Four pigtailed macaques were trained in a new two-choice olfactory discrimi nation method. They learned the initial task within 3 months, requiring a m aximum 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 lo w as 1:10 000. They were able to perceive iso-amyl acetate up to a 30 000-f old dilution (animals F1 and M2), respectively in a 30 Mio-fold dilution (a nimal M1). The sensitivity for n-pentanoic acid ranged between a dilution o f 1:30 000 (F1), 1:100 000 (M2), and 1:300 000 (M1). A comparison withthe t hresholds of other species demonstrates that the olfactory sensitivity of p igtailed macaques is not necessarily inferior to that of species that are b elieved to have a very keen sense of smell, such as dogs and rats. The sens itivity for certain odors seems to reflect their biological relevance for t he 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 m acaques using a multiple olfactory discrimination method indicates that the new two-choice discrimination method is a better candidate for the assessm ent of olfactory abilities in pigtailed macaques. (C) 2001 Elsevier Science Inc. All rights reserved.