Enantioselectivity of odor perception in squirrel monkeys and humans

With use of a conditioning paradigm, the ability of six squirrel monkeys to distinguish between 10 pairs of enantiomers, i.e., odorants that are identical except for chirality, was investigated. As a group, the animals were only able to discriminate between the optical isomers of alpha-pinene, carvone, limonene, and fenchone, whereas they failed to distinguish between the (+) and (-) forms of beta-citronellol, menthol, rose oxide, 2-butanol, alpha-terpineol, and camphor. With use of a triple forced-choice procedure, 10 human subjects were tested for their ability to discriminate between the same enantiomeric odor pairs in parallel and, with the exception of fenchone, showed a very similar pattern of performance compared with the squirrel monkeys. These findings support the assumption that human and nonhuman primates may share common principles of odor quality perception. Furthermore, the results suggest that, in both species, enantioselective molecular odor receptors may only exist for some, but not all volatile enantiomers and thus that chiral recognition of odorants is not a general phenomenon, but may be restricted to some substances.