Matthias Laska

Odor structure-activity relationships of carboxylic acids correspond between squirrel monkeys and humans

With use of a conditioning paradigm, the ability of four squirrel monkeys to distinguish n-valeric acid from n-forms and isoforms of other carboxylic acids (acetic acid to octanoic acid) was investigated. All four animals were clearly able to discriminate between all odor pairs tested and showed a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length of the carboxylic acids. Branching of the carbon chain was also found to affect odorant quality because all animals performed better in discriminating n-valeric acid from isoforms of other carboxylic acids compared with the corresponding n-forms of these substances. With use of a triple forced-choice procedure, 10 human subjects were tested on the same tasks in parallel and showed a very similar pattern of discrimination performance compared with the squirrel monkeys. Thus the results of this study provide evidence of well-developed olfactory discrimination ability in squirrel monkeys for carboxylic acids and support the assumption that human and nonhuman primates may share common principles of odor quality perception.

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.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 α-pinene, carvone, limonene, and fenchone, whereas they failed to distinguish between the (+) and (-) forms of β-citronellol, menthol, rose oxide, 2-butanol, α-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.

Olfactory Sensitivity for Aliphatic Esters in Spider Monkeys (Ateles geoffroyi)

Using a conditioning paradigm, the authors investigated the olfactory sensitivity of 3 spider monkeys (Ateles geoffroyi) for a homologous series of aliphatic esters (ethyl acetate to n-octyl acetate) and isomeric forms of some of these substances. With all odorants, the monkeys significantly discriminated concentrations below 1 ppm from the odorless solvent, and in several cases, individual monkeys even demonstrated thresholds below 1 ppb. The results showed spider monkeys to have a high olfactory sensitivity for aliphatic esters, which for the majority of substances matches or even is better than that of species such as the rat, the mouse, or the dog. These findings support the assumption that between-species comparisons of neuroanatomical features are poor predictors of olfactory performance.

Successful acquisition of an olfactory discrimination paradigm by spider monkeys, Ateles geoffroyi

The present study demonstrates that an operant conditioning paradigm-originally designed for assessing olfactory performance in an Old World primate, the pigtail macaque-can successfully be adapted for use with a New World primate, the spider monkey. Using a task based on a food-rewarded, two-choice discrimination of simultaneously presented odor stimuli, Ateles geoffroyi is capable of learning to discriminate between objects on the basis of odor cues. Moreover, animals could readily transfer to new S+ and S- stimuli, and could remember the significance of previously learned odor stimuli even after a 4-week break. We could also show that this method is suitable for obtaining reliable measures of olfactory sensitivity. Our results indicate that A. geoffroyi clearly outperforms Macaca nemestrina with regard to the speed of initial task acquisition and the ability to master transfer tasks, and shows a sensitivity to a food-related odorant which matches that of other primate species.

Odor structure-activity relationships compared in human and nonhuman primates.

The ability of 4 squirrel monkeys to distinguish between members of 3 homologous series of substances (aliphatic alcohols, aldehydes, and ketones) was investigated, and their performance was compared with that of a group of 10 human participants. With all 3 substance classes, and in both species, a significant negative correlation was found between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length. These findings suggest carbon chain length of aliphatic odorants to be one of presumably several determinants of the interaction between stimulus molecule and olfactory receptor and support the assumption that human and nonhuman primates may share common mechanisms of odor quality perception.

Unilateral olfactory perception and magical ideation

We assessed olfactory detection thresholds and discrimination abilities in 40 healthy right-handers (20 women and 20 men). All subjects were also required to complete the Magical Ideation (MI) scale, a well-validated 30-item schizotypy inventory. Over both nostrils, we found elevated thresholds for subjects with high MI scores (at or above the median score of 9.0) compared with those with low scores. In men but not women, specifically left-nostril acuity was inversely correlated to MI raw scores. MI was unrelated to olfactory discrimination performance. These results suggest an association, at least in healthy men, between even moderate signs of schizotypy and deficits in odor detection. The selective impairment of left-nostril performance adds to the growing evidence for left temporal lobe functional abnormalities in people high on MI. This laterality effect is known from previous studies in patients with schizophrenia. However, as a rule, in psychiatric patients olfactory identification rather than simple detection performance was found to be impaired, indicating that the integration of odor information is affected at different levels of processing in schizotypy compared with schizophrenia. Work with completely normal subjects may reasonably complement clinical studies of olfactory perception. Among its advantages are the good subject compliance and the absence of medication effects.

Different forms of human odor memory: a developmental study

Recognizing odors is an important biological function, both in the animal kingdom as well as for humans. It has been debated whether there exist different forms of human odor memory. For verbal memory, the concept of recollection and familiarity for conscious and unconscious recognition is widely accepted. Here we introduce a similar model for human odor memory. We use a combination of an odor naming and odor recognition memory task to estimate the relationship between depth of processing and retention of olfactory information. A developmental approach with children, young adults, middle aged adults and elderly subjects was chosen in order to study the influence of age. Our results indicate the existence of two separable forms of odor memory depending on whether the odors were correctly or incorrectly named during the naming task. These two forms of odor memory were differently represented across the human age range. Intact familiarity-based memory was found in all age groups, whereas memory based on recollection was impaired in the elderly and not yet fully developed in children. Our data show, for the first time, two different forms of human odor memory across the human life span.

Olfactory discrimination ability for homologous series of aliphatic ketones and acetic esters

We tested the ability of human subjects to distinguish between members of homologous series of aliphatic ketones (2-butanone to 2-decanone) and acetic esters (ethyl acetate to n-octyl acetate). In a forced-choice triangular test procedure, 20 subjects per series were repeatedly presented with all 21 binary combinations of the seven stimuli and asked to identify the bottle containing the odd stimulus. We found (a) that as a group, the subjects performed significantly above chance level in all tasks but three with the ketones, and all tasks but six with the acetic esters, and thus were clearly able to discriminate between most of the odor pairs presented; (b) marked interindividual differences in discrimination performance, ranging from subjects who were able to significantly distinguish between all 21 odor pairs of a series to subjects who failed to do so with the majority of tasks; and (c) a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length for both homologous series. In line with findings of two previous studies using homologous series of aliphatic alcohols, aldehydes, and carboxylic acids, our results suggest that carbon chain length may generally be an important determinant of the interaction between stimulus molecule and receptor, and thus may generally be a molecular property affecting odor quality of aliphatic substances.

Enantioselectivity of Odor Perception in Honeybees (Apis mellifera carnica)

The authors tested the ability of 60 free-flying honeybees (Apis mellifera carnica) to discriminate a conditioning odor from an array of 26 simultaneously presented substances. The stimuli included 10 pairs of enantiomers and 6 essential oils. The bees (a) significantly distinguished between 98% of the 540 odor pairs tested, thus showing an excellent overall discrimination performance, and (b) were able to discriminate between the optical isomers of limonene, alpha-pinene, beta-citronellol, menthol, and carvone but failed to distinguish between the (+)- and (-)-forms of alpha-terpineol, camphor, rose oxide, fenchone, and 2-butanol. The findings support the assumptions that enantioselective molecular odor receptors may exist only for some volatile enantiomers and that insects and mammals may share common principles of odor quality perception, irrespective of their completely differing repertoires of olfactory receptors.

Food Preferences and Nutrient Composition in Captive Spider Monkeys, Ateles geoffroyi

We assessed the occurrence of food preferences in captive spider monkeys and analyzed whether their preferences correlate with nutrient composition. Using a two-alternative choice test, we repeatedly presented 7 Ateles geoffroyi with all possible binary combinations of 12 types of food that are part of their diet in captivity. They exhibited the following rank order of preference: avocado > sapodilla > pineapple > mango > papaya > melon > banana > apple > tomato > orange > carrot > cucumber. Correlational analyses revealed that this preference ranking is significantly positively correlated with total energy content, irrespective of the source of energy as neither total carbohydrate content nor protein or lipid content is significantly correlated with food preference. Further, food preferences are significantly negatively correlated with water content and positively correlated with the content of magnesium, copper and manganese. These results suggest that despite their high degree of frugivory and high taste sensitivity for soluble carbohydrates, spider monkeys are opportunistic feeders with regard to maximizing net gain of energy.