Information

Is stereo olfactory ability restricted to humans?


Most animals I see around seem to have two nostrils - humans, snakes, birds, fish… and so on. From reading online I see that 2 nostrils provide a stereo olfactory effect. This stereo effect is caused by the difference in flow of air through the nostrils.

Does this stereo effect apply only to humans? Are there any animals that have a different number of nostrils? Say, more than 2, or less.


Moles and rats also smell in stereo (Catania 2013 and Rajan et al 2006), as do desert ants (link). The latter is rather interesting, given that ants "smell" using their antennae, which suggests multiple sensory structures, not necessarily nostrils, are required for stereo olfactory ability.

EDIT: Hammerhead sharks have two nares and also stereo olfactory ability (here). Dolphins have one spiracle, as do a number of other cetaceans.

It's actually not clear whether humans have stereo olfactory ability, (see edit below) as the "stereo" aspect derives from having nostrils that are sampling from different spatial locations. However, the research in the eastern mole suggests that this is not so far-fetched an idea, as their nostrils are not so far apart.

EDIT of EDIT: I take that back about humans: we do appear to have stereo olfaction.


Olfaction

Olfaction , or the sense of smell, is an ancient sensory system that together with taste enables an organism to detect chemicals in the external environment. Olfaction is present in most species such as insects, worms, fish, amphibians, birds, and mammals. It is essential for survival by permitting the location of food, mates, and predators, although in humans, olfaction is often viewed as an esthetic sense capable of triggering emotion and memory. In mammals, the sense of smell is mediated by two main sensory organs that are located in the nasal cavity: the main olfactory epithelium (MOE), which binds odorants, and the vomeronasal organ (VNO), which is responsible for pheromone detection. This review will focus on genetic aspects of the conscious perception of odors mediated by the MOE. In terrestrial vertebrates, odorants are volatile chemicals of various classes (aliphatic, cyclic, aromatic, etc.). The olfactory perception starts when odorants bind to olfactory receptors (ORs) that are expressed on cilia of the dendrites of olfactory sensory neurons (OSNs), which emerge in the MOE. This interaction induces the activation of a transduction pathway that involves a G-protein-dependent elevation of cyclic 3′, 5′ adenosine monophosphate (cAMP) opening ion channels that in turn results in the transmission of action potentials to specialized glomeruli localized in the olfactory bulb. Sensory inputs are then transmitted to the olfactory cortex where the information is integrated to result in the sensation of smell. A number of reviews have been published on the principles of olfaction ( Moulton, 1967 Keverne, 1999 Krieger and Breer, 1999 Laurent, 1999 Mombaerts, 1999, 2001a , 2004a Mori et al., 1999 Firestein, 2001 Gaillard et al., 2004a ).

During the past 6 years, different studies on the evolution of the OR genes in mammals have pointed out the reduction of the functional fraction of the OR gene repertoire during primate evolution leading to a restricted set of functional OR genes in humans (see Evolution of Vertebrate Olfactory Subsystems ). These observations led to the hypothesis that the size of the functional OR repertoire reflects the olfactory needs and hence the olfactory capacity/ability of an organism.

This review is an overview on the subject by comparing data obtained by the analysis of the OR subgenome of different primate species with respect to that of mouse and dog.


Biology 1002 (Final) Ch 35

After reading the paragraphs below, answer the questions that follow.

A researcher is investigating the ability of salmon to migrate thousands of miles in the ocean yet return to the location where they were hatched to spawn. Data from experiments suggest that more than one type of homing mechanism may be involved in this behavior. When salmon arrive at a river mouth from the open sea, they appear to use olfactory cues to find their home streams, but how do they find their way back to the correct spot along the coastline from the open ocean?

Several experiments were carried out to test the hypothesis that geomagnetic factors (the influence of Earth's magnetic field) play a key role in the ability of salmon to find the proper location along the coast. In one such experiment, salmon hatched in Ketchikan, Alaska were subjected to the geomagnetic characteristics of a different location on the Alaska Peninsula, Cold Bay. The fish were then released to determine to which of the two locations they would return to spawn.

After reading the paragraphs below, answer the questions that follow.

A researcher is investigating the ability of salmon to migrate thousands of miles in the ocean yet return to the location where they were hatched to spawn. Data from experiments suggest that more than one type of homing mechanism may be involved in this behavior. When salmon arrive at a river mouth from the open sea, they appear to use olfactory cues to find their home streams, but how do they find their way back to the correct spot along the coastline from the open ocean?

Several experiments were carried out to test the hypothesis that geomagnetic factors (the influence of Earth's magnetic field) play a key role in the ability of salmon to find the proper location along the coast. In one such experiment, salmon hatched in Ketchikan, Alaska were subjected to the geomagnetic characteristics of a different location on the Alaska Peninsula, Cold Bay. The fish were then released to determine to which of the two locations they would return to spawn.

In examining the effects of atrazine, one of the most commonly used herbicides in the world, scientists studied the mating behavior of male frogs exposed to atrazine (Atr) compared to a group that was not exposed (Non). The results are shown in the figure.


Gender-specific induction of enhanced sensitivity to odors

Induction of olfactory sensitivity in humans was first illustrated when men and women who were initially unable to smell the volatile steroid androstenone (5α-androst-16-en-3-one) developed that ability after repeated, brief exposures 1 . Because this finding has not been replicated with other compounds in humans, it has been assumed that olfactory induction is a narrowly constrained phenomenon, occurring only in individuals with specific anosmias, perhaps only to androstenone (compare ref. 2). Here we show that induction of enhanced olfactory sensitivity seems to be a more general phenomenon, with marked changes in olfactory acuity occurring during repeated test exposures to several odorants among people with average baseline sensitivity to these compounds. This increased sensitivity (averaging five orders of magnitude) was observed only among females of reproductive age. These observations provide convincing evidence that female olfactory acuity to a variety of odorants can vastly improve with repeated test exposures. They also suggest a sensory basis for the anecdotal observation of greater olfactory sensitivities among females and raise the possibility that the olfactory-induction process may be associated with female reproductive behaviors such as pair bonding and kin recognition.


Footnotes

Electronic supplementary material is available online at https://doi.org/10.6084/m9.figshare.c.4874640.

One contribution of 18 to a Theo Murphy meeting issue ‘Olfactory communication in humans’.

Published by the Royal Society. All rights reserved.

References

Cahill L, Babinsky R, Markowitsch HJ, McGaugh JL

. 1995 The amygdala and emotional memory . Nature 377, 295-296. (doi:10.1038/377295a0) Crossref, PubMed, ISI, Google Scholar

. 2002 Neural systems for recognizing emotion . Curr. Opin. Neurobiol. 12, 169-177. (doi:10.1016/S0959-4388(02)00301-X) Crossref, PubMed, ISI, Google Scholar

. 2003 Affect and face perception: odors modulate the recognition advantage of happy faces . Emotion 3, 315-326. (doi:10.1037/1528-3542.3.4.315) Crossref, PubMed, ISI, Google Scholar

Lemogne C, Smadja J, Zerdazi E-H, Soudry Y, Robin M, Berthoz S, Limosin F, Consoli SM, Bonfils P

. 2015 Congenital anosmia and emotion recognition: a case-control study . Neuropsychologia 72, 52-58. (doi:10.1016/J.NEUROPSYCHOLOGIA.2015.04.028) Crossref, PubMed, ISI, Google Scholar

Croy I, Bojanowski V, Hummel T

. 2013 Men without a sense of smell exhibit a strongly reduced number of sexual relationships, women exhibit reduced partnership security – a reanalysis of previously published data . Biol. Psychol. 92, 292-294. (doi:10.1016/j.biopsycho.2012.11.008) Crossref, PubMed, ISI, Google Scholar

2011 Smelling chemosensory signals of males in anxious versus nonanxious condition increases state anxiety of female subjects . Chem. Senses 36, 19-27. (doi:10.1093/chemse/bjq087) Crossref, PubMed, ISI, Google Scholar

. 2006 Chemosignals of fear enhance cognitive performance in humans . Chem. Senses 31, 415-423. (doi:10.1093/chemse/bjj046) Crossref, PubMed, ISI, Google Scholar

de Groot JHB, Smeets MAM, Kaldewaij A, Duijndam MJA, Semin GR

. 2012 Chemosignals communicate human emotions . Psychol. Sci. 23, 1417-1424. (doi:10.1177/0956797612445317) Crossref, PubMed, ISI, Google Scholar

Prehn A, Ohrt A, Sojka B, Ferstl R, Pause BM

. 2006 Chemosensory anxiety signals augment the startle reflex in humans . Neurosci. Lett. 394, 127-130. (doi:10.1016/j.neulet.2005.10.012) Crossref, PubMed, ISI, Google Scholar

. 1999 Rapid mood change and human odors . Physiol. Behav. 68, 241-250. (doi:10.1016/S0031-9384(99)00147-X) Crossref, PubMed, ISI, Google Scholar

2007 Individual and gender fingerprints in human body odour . J. R. Soc. Interface 4, 331-340. (doi:10.1098/rsif.22006.0182) Link, ISI, Google Scholar

. 1977 The importance of human odour in non-verbal communication . Z. Tierpsychol. 43, 225-238. (doi:10.1111/j.1439-0310.1977.tb00072.x) Crossref, PubMed, Google Scholar

. 1980 Personal odor and nonverbal communication . Ethol. Sociobiol. 1, 225-231. (doi:10.1016/0162-3095(80)90009-6) Crossref, ISI, Google Scholar

Mahmut MK, Stevenson RJ, Stephen I

. 2019 Do women love their partner's smell? Exploring women's preferences for and identification of male partner and non-partner body odor . Physiol. Behav. 210, 112517 (doi:10.1016/J.PHYSBEH.2019.04.006) Crossref, PubMed, ISI, Google Scholar

. 2013 Assessing personality using body odor: differences between children and adults . J. Nonverbal Behav. 37, 153-163. (doi:10.1007/s10919-013-0152-2) Crossref, PubMed, ISI, Google Scholar

. 2013 Seeing or smelling? Assessing personality on the basis of different stimuli . Pers. Individ. Differ. 55, 175-179. (doi:10.1016/j.paid.2013.02.026) Crossref, ISI, Google Scholar

2015 Individual olfactory perception reveals meaningful nonolfactory genetic information . Proc. Natl Acad. Sci. USA 112, 8750-8755. (doi:10.1073/pnas.1424826112) Crossref, PubMed, ISI, Google Scholar

Carvalho Santos PS, Schinemann JA, Gabardo J, Da Graça Bicalho M

. 2005 New evidence that the MHC influences odor perception in humans: a study with 58 Southern Brazilian students . Horm. Behav. 47, 384-388. (doi:10.1016/j.yhbeh.2004.11.005) Crossref, PubMed, ISI, Google Scholar

Wedekind C, Seebeck T, Bettens F, Paepke AJ

. 1995 MHC-dependent mate preferences in humans . Proc. R. Soc. Lond. B 260, 245-249. (doi:10.1098/rspb.1995.0087) Link, ISI, Google Scholar

. 1997 Body odour preferences in men and women: do they aim for specific MHC combinations or simply heterozygosity? Proc. R. Soc. Lond. B 264, 1471-1479. (doi:10.1098/rspb.1997.0204) Link, ISI, Google Scholar

Roberts SC, Gosling LM, Carter V, Petrie M

. 2008 MHC-correlated odour preferences in humans and the use of oral contraceptives . Proc. R. Soc. B 275, 2715-2722. (doi:10.1098/rspb.2008.0825) Link, ISI, Google Scholar

Havlícek J, Winternitz J, Roberts SC

. 2020 Major histocompatibility complex-associated odour preferences and human mate choice: near and far horizons . Phil. Trans. R. Soc. B 375, 20190260. (doi:10.1098/rstb.2019.0260) Link, Google Scholar

Allen C, Cobey KD, Havlíček J, Singleton FP, Hahn AC, Moran CN, Roberts SC

. 2019 Preparation for fatherhood: a role for olfactory communication during human pregnancy? Physiol. Behav. 206, 175-180. (doi:10.1016/J.PHYSBEH.2019.03.030) Crossref, PubMed, ISI, Google Scholar

Porter RH, Balogh RD, Cernoch JM, Franchi C

. 1986 Recognition of kin through characteristic body odors . Chem. Senses 11, 389-395. (doi:10.1093/chemse/11.3.389) Crossref, ISI, Google Scholar

Porter RH, Cernoch JM, McLaughlin FJ

. 1983 Maternal recognition of neonates through olfactory cues . Physiol. Behav. 30, 151-154. (doi:10.1016/0031-9384(83)90051-3) Crossref, PubMed, ISI, Google Scholar

Croy I, Landis BN, Meusel T, Seo H-S, Krone F, Hummel T

. 2011 Patient adjustment to reduced olfactory function . Arch. Otolaryngol. Head Neck Surg. 137, 377-382. (doi:10.1001/archoto.2011.32) Crossref, PubMed, Google Scholar

2017 Position paper on olfactory dysfunction . Rhinology 54, 1-30. (doi:10.4193/Rhin16.248) PubMed, ISI, Google Scholar

Katotomichelakis M, Simopoulos E, Tripsianis G, Prokopakis E, Danielides G, Velegrakis SG, Livaditis M, Danielides V

. 2013 Improvement of olfactory function for quality of life recovery . Laryngoscope 123, E10-E16. (doi:10.1002/lary.24113) Crossref, PubMed, ISI, Google Scholar

Litvack JR, Mace JC, Smith TL

. 2009 Olfactory function and disease severity in chronic rhinosinusitis . Am. J. Rhinol. Allergy 23, 139-144. (doi:10.2500/ajra.2009.23.3286) Crossref, PubMed, ISI, Google Scholar

Miwa T, Furukawa M, Tsukatani T, Costanzo RM, DiNardo LJ, Reiter ER

. 2001 Impact of olfactory impairment on quality of life and disability . Arch. Otolaryngol. Head Neck Surg. 127, 497-503. (doi:10.1001/archotol.127.5.497) Crossref, PubMed, Google Scholar

Neuland C, Bitter T, Marschner H, Gudziol H, Guntinas-Lichius O

. 2011 Health-related and specific olfaction-related quality of life in patients with chronic functional anosmia or severe hyposmia . Laryngoscope 121, 867-872. (doi:10.1002/lary.21387) Crossref, PubMed, ISI, Google Scholar

. 2014 The impact of olfactory disorders in the United Kingdom . Chem. Senses 39, 711-718. (doi:10.1093/chemse/bju043) Crossref, PubMed, ISI, Google Scholar

Smeets MAM, Veldhuizen MG, Galle S, Gouweloos J, de Haan A-MJA, Vernooij J, Visscher F, Kroeze JHA

. 2009 Sense of smell disorder and health-related quality of life . Rehabil. Psychol. 54, 404-412. (doi:10.1037/a0017502) Crossref, PubMed, ISI, Google Scholar

Shu CH, Lee PO, Lan MY, Lee YL

. 2011 Factors affecting the impact of olfactory loss on the quality of life and emotional coping ability . Rhinology 49, 337-341. (doi:10.4193/Rhino10.130) PubMed, ISI, Google Scholar

Oleszkiewicz A, Schriever VA, Croy I, Hähner A, Hummel T

. 2019 Updated Sniffin’ Sticks normative data based on an extended sample of 9139 subjects . Eur. Arch. Otorhinolaryngol. 276, 719-728. (doi:10.1007/s00405-018-5248-1) Crossref, PubMed, ISI, Google Scholar

Mattos JL, Schlosser RJ, Storck KA, Soler ZM

. 2017 Understanding the relationship between olfactory-specific quality of life, objective olfactory loss, and patient factors in chronic rhinosinusitis . Int. Forum Allergy Rhinol. 7, 734-740. (doi:10.1002/alr.21940) Crossref, PubMed, ISI, Google Scholar

Faul F, Erdfelder E, Lang A, Buchner A

. 2007 G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences . Behav. Res. Methods 39, 175-191. (doi:10.3758/bf03193146) Crossref, PubMed, ISI, Google Scholar

Welge-Luessen A, Leopold D, Miwa T

. 2013 Smell and taste disorders diagnostic and clinical work-up . In Management of smell and taste disorders—a practical guide for clinicians (eds

), pp. 49-57. Stuttgart, Germany : Thieme Verlagsgruppe . Google Scholar

Croy I, Buschhüter D, Seo H-S, Negoias S, Hummel T

. 2010 Individual significance of olfaction: development of a questionnaire . Eur. Arch. Otorhinolaryngol. 267, 67-71. (doi:10.1007/s00405-009-1054-0) Crossref, PubMed, ISI, Google Scholar

Nucci M, Mapelli D, Mondini S

. 2012 Cognitive reserve index questionnaire (CRIq): a new instrument for measuring cognitive reserve . Aging Clin. Exp. Res. 24, 218-226. (doi:10.3275/7800) PubMed, Google Scholar

Nasreddine ZS, Phillips NA, Bédirian V, Charbonneau S, Whitehead V, Collin I, Cummings JL, Chertkow H

. 2005 The Montreal Cognitive Assessment, MoCA: a brief screening tool for mild cognitive impairment . J. Am. Geriatr. Soc. 53, 695-699. (doi:10.1111/j.1532-5415.2005.53221.x) Crossref, PubMed, ISI, Google Scholar

Brazier JE, Harper R, Jones NM, O'Cathain A, Thomas KJ, Usherwood T, Westlake L

. 1992 Validating the SF-36 health survey questionnaire: new outcome measure for primary care . BMJ 305, 160-164. (doi:10.1136/bmj.305.6846.160) Crossref, PubMed, Google Scholar

. 1992 The MOS 36-item short-form health survey (SF-36): I. Conceptual framework and item selection on JSTOR . Med. Care 30, 473-483. (doi:10.1097/00005650-199206000-00002) Crossref, PubMed, ISI, Google Scholar

Beck AT, Steer RA, Carbin MG

. 1988 Psychometric properties of the Beck Depression Inventory: twenty-five years of evaluation . Clin. Psychol. Rev. 8, 77-100. (doi:10.1016/0272-7358(88)90050-5) Crossref, ISI, Google Scholar

Hummel T, Sekinger B, Wolf SR, Pauli E, Kobal G

. 1997 ‘Sniffin’ Sticks’: olfactory performance assessed by the combined testing of odour identification, odor discrimination and olfactory threshold . Chem. Senses 22, 39-52. (doi:10.1093/chemse/22.1.39) Crossref, PubMed, ISI, Google Scholar

Ottaviano G, Scadding GK, Coles S, Lund VJ

. 2006 Peak nasal inspiratory flow normal range in adult population . Rhinology 44, 32-35. (doi:10.4193/rhin12.071) PubMed, ISI, Google Scholar

Bahar-Fuchs A, Moss S, Rowe C, Savage G

. 2011 Awareness of olfactory deficits in healthy aging, amnestic mild cognitive impairment and Alzheimer's disease . Int. Psychogeriatr. 23, 1097-1106. (doi:10.1017/S1041610210002371) Crossref, PubMed, ISI, Google Scholar

Landis BN, Hummel T, Hugentobler M, Giger R, Lacroix JS

. 2003 Ratings of overall olfactory function . Chem. Senses 28, 691-694. (doi:10.1093/chemse/bjg061) Crossref, PubMed, ISI, Google Scholar

Nordin S, Monsch AU, Murphy C

. 1995 Unawareness of smell loss in normal aging and Alzheimer's disease: discrepancy between self-reported and diagnosed smell sensitivity . J. Gerontol. B Psychol. Sci. Soc. Sci. 50, 187-192. (doi:10.1093/geronb/50B.4.P187) Crossref, ISI, Google Scholar

. 2010 Human olfaction: a constant state of change-blindness . Exp. Brain Res. 205, 13-29. (doi:10.1007/s00221-010-2348-6) Crossref, PubMed, ISI, Google Scholar

Wehling E, Nordin S, Espeseth T, Reinvang I, Lundervold AJ

. 2011 Unawareness of olfactory dysfunction and its association with cognitive functioning in middle aged and old adults . Arch. Clin. Neuropsychol. 26, 260-269. (doi:10.1093/arclin/acr019) Crossref, PubMed, ISI, Google Scholar

2004 Riechstörungen: epidemiologie, pathophysiologische klassifikation, diagnose und therapie . HNO 52, 679-684. (doi:10.1007/s00106-004-1117-x) Crossref, PubMed, ISI, Google Scholar

. 2005 Olfactory dysfunction and daily life . Eur. Arch. Otorhinorlaryngol. 262, 231-235. (doi:10.1007/s00405-004-0796-y) Crossref, PubMed, ISI, Google Scholar

. 1989 National geographic smell survey: effects of age are heterogenous . Ann. N.Y. Acad. Sci. 561, 12-28. (doi:10.1111/j.1749-6632.1989.tb20966.x) Crossref, PubMed, ISI, Google Scholar

. 2019 Whose nose does not know? Demographical characterization of people unaware of anosmia . Eur. Arch. Otorhinolaryngol. 276, 1849-1852. (doi:10.1007/s00405-019-05414-8) Crossref, PubMed, ISI, Google Scholar

Wehling E, Lundervold AJ, Espeset T, Reinvang I, Bramerson A, Nordin S

. 2015 Even cognitively well-functioning adults are unaware of their olfactory dysfunction: implications for ENT clinicians and researchers . Rhinology 53, 89-94. (doi:10.4193/Rhin14.081) Crossref, PubMed, ISI, Google Scholar

. 2014 Olfactory disorders and quality of life—an updated review . Chem. Senses 39, 185-194. (doi:10.1093/chemse/bjt072) Crossref, PubMed, ISI, Google Scholar

. 2005 Olfactory disorders and their consequences for quality of life . Acta Otolaryngol. 125, 116-121. (doi:10.1080/00016480410022787) Crossref, PubMed, ISI, Google Scholar

Sorokowska A, Oleszkiewicz A, Sorokowski P

. 2018 A compensatory effect on mate selection? Importance of auditory, olfactory, and tactile cues in partner choice among blind and sighted individuals . Arch. Sex. Behav. 47, 597-603. (doi:10.1007/s10508-018-1156-0) Crossref, PubMed, ISI, Google Scholar

Haehner A, Hummel T, Reichmann H

. 2009 Olfactory dysfunction as a diagnostic marker for Parkinson's disease . Expert Rev. Neurother. 9, 1773-1779. (doi:10.1586/ern.09.115) Crossref, PubMed, ISI, Google Scholar

Mesholam RI, Moberg PJ, Mahr RN, Doty RL

. 1998 Olfaction in neurodegenerative disease: A meta-analysis of olfactory functioning in Alzheimer's and Parkinson's diseases . Arch. Neurol. 55, 84-90. (doi:10.1001/archneur.55.1.84) Crossref, PubMed, Google Scholar

Wegener B-A, Croy I, Hähner A, Hummel T

. 2018 Olfactory training with older people . Int. J. Geriatr. Psychiatry 33, 212-220. (doi:10.1002/gps.4725) Crossref, PubMed, ISI, Google Scholar


Discussion

The results of this study demonstrate that the ability of human subjects to discriminate between enantiomeric odor pairs is substance-specific and thus not a generalizable phenomenon. Whereas almost all subjects had few difficulties in distinguishing the (+)- and the (−)-forms of α-pinene, carvone and limonene, most panelists failed to discriminate between the antipodes of β-citronellol, menthol, fenchone, rose oxide, camphor,α -terpineol and 2-butanol when presented at equal concentrations.

They are also in line with reports which assigned the same verbal labels to the antipodes of menthol ( Doll and Bournot, 1949 Beets, 1978 Eccles, 1990), citronellol ( Maas et al., 1993), camphor ( Theimer et al., 1977 Simmons et al., 1992 Ohloff, 1994), fenchone ( Ohloff, 1994) and 2-butanol ( Ohloff, 1994).

On the contrary, our findings do not agree with reports which assigned different verbal labels to the enantiomers of menthol and α-terpineol ( Beets, 1978 Koppenhoefer et al., 1994), and to the optical isomers of citronellol ( Ohloff, 1972, 1994) and rose oxide ( Ohloff, 1972 Pickenhagen, 1989). They also differ from reports which assigned the same verbal labels to the antipodes ofα -pinene ( Ohloff, 1994).

The fact that different authors came to contradictory conclusions with regard to the equality or inequality of qualitative attributes assigned to several of the enantiomeric odor pairs employed here (α-pinene, menthol and citronellol) reflects the fundamental problem of semantic ambiguity in the verbal description of odor quality and illustrates the need for more unequivocal means of assessing qualitative similarities and differences between odorants.

The few studies which have so far used discrimination procedures to assess the ability of humans to detect differences between enantiomeric odor pairs are generally in agreement with our findings. Jones and Velasquez ( 1974), Pike et al. ( 1987, 1988), Cowart ( 1990) and Hormann and Cowart ( 1993) all reported the (+)- and (−)-forms of carvone to be readily discriminable both when presented at equal concentrations and when stimulus intensity of one of the discriminants was intentionally altered. Using a triangular test procedure similar to the one employed here, Cowart ( 1990) also found that humans are unable to discriminate between the antipodes of fenchone.

In the only study so far that has employed an array of chiral odor pairs, Jones and Elliot ( 1975) reported the ability of human subjects to discriminate between enantiomers to be both substance-specific and subject-specific. In line with our results, the majority of their subjects were able to distinguish the antipodes of carvone and of α-pinene. Their finding of 2-butanol—which was significantly discriminated by only 1 out of 20 subjects in our study—to be discriminable from its mirror image, however, was based on invalid statistics as the authors applied binomial tests to the total number of correct responses pooled from all subjects. Converted to percentages, their summed score for this odor pair corresponds to 40.3% decisions correct, which compares favorably with our finding of an average score of 37.5%.

The same authors reported large differences in discrim- ination performance between subjects. Unfortunately, they gave no detailed information but only stated that 7 of their 31 subjects failed to reach a significant overall score which the authors discussed as a‘ general chiral anosmia’ ( Jones and Elliot, 1975). We also found considerable interindividual variability both with individual odor pairs (cf. SDs in Figure 1) and across tasks (cf. Figure 2). However, the across-task patterns of performance were very similar between subjects, with virtually all individuals scoring better withα -pinene, carvone and limonene than with the other tasks. This suggests that the substance-specificity of the ability to discriminate between enantiomeric odor pairs is a robust phenomenon.

It is well-established that both the olfactory and trigeminal systems contribute to the perception of the majority of odorants ( Doty, 1995). This raises the possibility that the nasal trigeminal system might have contributed to the discrimination of the enantiomers of α-pinene, carvone and limonene, a possibility which is supported by the finding that congenitally anosmic subjects possess at least a coarse ability to distinguish between odorants using sensory information provided by their fifth cranial nerve ( Laska et al., 1997). The results of experiment 2, however, strongly suggest that the substances used here had little if any trigeminal-stimulating properties at the concentrations tested and that in any case the antipodes of a given substance did not differ in their degree of trigeminality. Thus, the possibility of trigeminal involvement in the discrimination of the three enantiomeric odor pairs in question can be excluded.

The possibility that differences in perceived odor intensity might have contributed to the discrimination performance also seems quite unlikely as >90% of the subjects' decisions involving the three odor pairs that were significantly discriminated at the group level in experiment 1 were reported to be based on perceived differences in odor quality rather than odor intensity (cf. Test procedure). Further, the comparatively few instances in which perceived differences in odor intensity were reported seem to reflect a subject's difficulty to discriminate at all, as error rates in such cases tended to be higher compared with the regular case of reported differences in odor quality. The same tendency for higher error rates with reports of perceived differences in odor intensity rather than odor quality as a choice criterion has been found in studies assessing the discriminability of members of homologous series of aliphatic alcohols ( Laska and Trolp, 1998) and carboxylic acids ( Laska and Teubner, 1998). The results of experiment 3 lend additional support to the assumption that possible differences in odor intensity did not contribute to discrimination performance as detection thresholds for the enantiomers of α-pinene and the antipodes of limonene did not differ from each other (cf. Figure 7). Our finding that (−)-carvone yielded significantly lower threshold values than (+)-carvone in three of the five test sessions is in line with earlier studies ( Leitereg et al., 1971a, b Cowart, 1990 Hormann and Cowart, 1993) reporting the same discrepancy with these stimuli. However, Cowart ( 1990) also reported suprathreshold concentrations of (+)-carvone to be more intense than its mirror image and discriminability to be largely unaffected by changes in the concentration of one of the discriminants.

Taken together, the results of experiments 2 and 3 suggest that the discrimination scores found with α-pinene, carvone and limonene reflect the ability of the human olfactory system to distinguish the odor qualities of these enantiomeric odor pairs.

A final aspect of the present study is the finding that no generalizable conclusions can be drawn from our data as to odor structure–activity relationships which would allow us to predict whether or not a given pair of enantiomers can be olfactorily discriminated. However, it was apparent that two of the three substances whose optical isomers were significantly distinguished (carvone and limonene) share a propenyl group at the chiral center and thus it would be worthwhile to include other enantiomeric odor pairs which show this structural feature in future studies of olfactory discrimination performance. Our finding that the antipodes ofα -pinene were also discriminable despite their lack of a propenyl group, on the other hand, illustrates that the presence or absence of a certain functional group at the chiral carbon atom is not a sufficient predictor of enantio-selectivity. Similarly, membership of a certain chemical class is not a predictor of whether or not the antipodes of a substance are discriminable as, for example, carvone, fenchone and camphor are all carbonyl compounds but differ significantly in their discriminability (cf. Figure 1).

A more biological explanation of why some enantiomeric odor pairs can be discriminated whereas others cannot is that enantioselectivity of the human olfactory system may be restricted to substances for which both optical isomers are widely present in our natural odor world. There is accumulating evidence that the mammalian olfactory system, analogous to the immune system, may be capable of increasing the expression of molecular receptors that are responsive to a given odorant after repeated exposure to that stimulus ( Wang et al., 1993 Semke et al., 1995). Thus it might be that chiral odorants for which only one of their antipodes is naturally occurring cannot be discriminated from their mirror images due to a lack of an appropriate enantioselective receptor. Analytical studies of essential oils ( König et al., 1990 Mosandl et al., 1990b) and fruit flavours ( Gessner et al., 1988 Mosandl et al., 1990a) have shown that the relative amounts found with the optical isomers of a chiral substance can vary widely. With menthol, for example, the levo-form prevails in all essential oils containing this compound whereas the dextro-form is found only in trace amounts ( Eccles et al., 1988). Carvone, α-pinene and limonene, on the other hand, are widely distributed with both their enantiomeric forms—although in different ratios—in a wide variety of plant extracts ( König et al., 1990 Mosandl et al., 1990b). Our finding that the optical isomers of the latter three substances were discriminable while those of menthol were not supports the hypothesis that a widespread occurrence of both enantiomeric forms of a substance in our odorous environment is a prerequisite for our ability to distinguish between these. However, in order to further corroborate this hypothesis it is clearly important to include other enantiomeric odor pairs in studies of olfactory discrimination performance and to compare these findings with the natural occurrence and distribution of such substances.

So far, the results of the present study provide evidence that the ability of humans to discriminate between enantiomeric odor pairs is substance-specific and thus support the assumption that enantioselective molecular odor receptors may only exist for some but not all volatile enantiomers.

Performance of 20 subjects in discriminating between 10 pairs of enantiomers. Each data point represents the percentage (means ± SD) of correct choices from 10 decisions per odor pair and subject. The figures above the abscissa indicate the number of subjects that failed to perform significantly above chance in the corresponding task.


Birds Have A Good Sense Of Smell

Sight and hearing are the most important senses for birds - this is at least the received wisdom. By studying bird DNA, however, researchers at the Max Planck Institute for Ornithology, along with a colleague at the Cawthron Institute in New Zealand, have now provided genetic evidence that many bird species have a well-developed sense of smell (Proceedings of the Royal Society B, 16.07.2008).

The sense of smell might indeed be as important to birds as it is to fish or even mammals. This is the main conclusion of a study by Silke Steiger (Max Planck Institute for Ornithology) and her colleagues. The sense of smell in birds was, until quite recently, thought to be poorly developed.

Recent behavioural studies have shown that some bird species use their sense of smell to navigate, forage or even to distinguish individuals. Silke Steiger and her colleagues chose a genetic approach for their study. Their research focused on the olfactory receptor (OR) genes, which are expressed in sensory neurons within the olfactory epithelium, and constitute the molecular basis of the sense of smell. The total number of OR genes in a genome may reflect how many different scents an animal can detect or distinguish. In birds such genetic studies were previously restricted to the chicken, hitherto the only bird for which the full genomic sequence is known.

In addition to the chicken, the researchers compared the OR genes of eight distantly related bird species. They estimated the total number of OR genes in each species&rsquo genome using a statistical technique adapted from ecological studies where it is used to estimate species diversity. They found considerable differences in OR gene number between the nine bird species. The brown kiwi from New Zealand, for example, has about six times more OR genes than the blue tit or canary.

"When we looked up the relative sizes of the olfactory bulb in the brain, we also noticed similar big differences between species", said Steiger. "It is likely that the number of OR genes correlates with the number of different smells that can be perceived. As the olfactory bulb is responsible for processing olfactory information, we were not too surprised to see that the number of genes is linked to the size of the olfactory bulb." Wide variation in numbers of OR genes, and sizes of olfactory bulbs, has also been found amongst mammals.

The implication of this finding is that different ecological niches may have shaped the OR gene repertoire sizes in birds, as has been suggested for mammals. The high number of OR genes in the kiwi could be explained by this bird&rsquos unusual ecological niche. Unique among birds, the nostrils of the night-active kiwi are at the tip of the bill. When kiwis probe the forest floor in search of food, they are guided by smell rather than sight. Indeed the snuffling, nocturnal kiwis are sometimes considered to be New Zealand&rsquos equivalent of a hedgehog!

Besides the total number of OR genes, the researchers estimated which proportion of these genes are functional. This was done because, in mammals, a reduced dependence on the sense of smell is associated with OR genes gradually accumulating mutations and so becoming non-functional. For example, in humans, which have a poor sense of smell compared with most other mammals, only about 40% of all OR genes may be functional. However, in the bird species studied by Steiger et al., the large majority of the OR genes were functional, again indicating that the sense of smell is much more important in birds than previously thought.

From the analysis of the chicken genome three years ago a new class of OR genes was found. Now Silke Steiger and her colleagues have shown that this class of genes seems to be a shared feature of all birds, while such OR genes are not found in other vertebrates such as fish, mammals or reptiles. The specific function of this class of bird-specific OR genes remains unknown.

Story Source:

Materials provided by Max-Planck-Gesellschaft. Note: Content may be edited for style and length.


Taste: Vertebrate Psychophysics

V.B. Duffy , . D.J. Snyder , in Encyclopedia of Neuroscience , 2009

Genetic Variation

Human psychophysical data are vital to provide meaning to taste receptor genetics and taste gene expression. The most-studied genetic trait involves variation in response to phenylthiocarbamide (PTC) and 6- n-propylthiouracil (PROP), members of the thiourea family. Taste blindness to PTC was an accidental finding by the chemist Fox in 1931. PROP is preferred today as a taste stimulus as it is safer and lacks an odor. PROP is not found in the food supply, leading to questions of its ecological validity however, related natural thioureas (e.g., 1-5-vinyl-2-thio-oxazolidone) are widely found in foods. Studies using PROP as a phenotypic marker have revealed associations with dietary and lifestyle behaviors and health outcomes.

PROP has become a marker for differences in overall oral sensation, probably not because of some unique receptor attribute, but because it shows large variability across individuals and because it highlights the importance of taste in the central integration of oral sensation. Some individuals live in a neon orosensory world (supertasters), and others live in a more pastel one (nontasters). Characterizing genetic variation in oral sensation could move to an expanded number of taste markers and emerging taste genotypes. For example, greater taster intensity has been characterized by other phenotypes, including response to some irritants and thermal stimulation.

Historically, PROP tasting was measured via threshold procedure, separating those who are insensitive from those who are tasters. Polymorphisms on the long arm of chromosome 7 for the TAS2R38 gene correspond well with PTC/PROP threshold classifications. Two homozygous and a heterozygous form are seen commonly in the population: The AVI/AVI homozygote corresponds to the PROP nontaster phenotype, while the PAV/AVI heterozygote and the PAV/PAV homozygote correspond to the taster phenotype. The perceived intensity of PROP or suprathreshold response corresponds less well with TAS2R38, not sufficiently differentiating individuals who taste PROP as bitter (i.e., medium tasters) from those who taste PROP as exceedingly bitter (i.e., supertasters). It is interesting that some AVI/AVI individuals taste concentrated PROP as bitter, which suggests with a high enough concentration, the hT2R38 receptor responds to PROP or that a second taste receptor is involved in PROP tasting. Some of the heightened bitterness of PROP can be explained through greater numbers of fungiform papillae, the type of taste papillae found on the anterior tongue. Those who taste PROP as bitter and extremely bitter have a high number of fungiform papillae, yet the heightened number of papillae may not fully explain PROP supertasting. Identification of other factors that may contribute to supertasting is an area of active research.

Supertasters of PROP perceive greater intensities to salty, sweet, sour, and bitter compounds. Because supertasters tend to have more fungiform papillae and these papillae hold pain and touch fibers as well as taste fibers, those who taste PROP as more bitter also experience more chemesthetic sensations from irritants (e.g., chili peppers, black pepper, ginger, carbonation, alcohol) and tactile sensations (e.g., creamy sensations from fat). PROP supertasters also experience greater retronasal sensations, especially if these sensations are congruent with taste sensations (e.g., sweet taste of sucrose with sweet odor of strawberries in strawberry jam). Thus, the term ‘supertaster’ could be operationalized as an individual who tastes PROP strongly bitter or has a high number of fungiform papillae, as well as a heightened response to other oral sensations.


The Functioning of Species-Specific Olfactory Pheromones in the Biology of a Mosquito-Eating Jumping Spider from East Africa

Having unique, complex eyes and vision based on exceptional spatial acuity, salticid spiders are known for their vision-based predatory and mating strategies. Yet Evarcha culicivora, the salticid we consider here, is known for predatory and mating strategies based strongly on the interplay of vision and olfaction. This unusual East African species feeds indirectly on vertebrate blood by choosing blood-carrying female mosquitoes as preferred prey, which it can identify by sight and by smell. Moreover, E. culicivora’s mating strategy is unusual because, unlike the prevailing general pattern among spiders, where males are more active in courtship and females are more active in mate choice, both roles are characteristic of both sexes of E. culicivora. There is also an unusual relationship between diet and mating in this species, with blood meals making both sexes more attractive as potential mates. However, findings from the present study demonstrate that, regardless of source-spider diet and even when restricted to using chemoreception in the absence of seeing another spider, both sexes can discriminate between opposite-sex conspecifics and opposite-sex heterospecifics. Yet there is no evidence that diet (blood versus no blood) influences the attractiveness of opposite-sex heterospecific individuals to E. culicivora. Evidence that the odor of opposite-sex conspecifics is salient to E. culicivora comes from three different experimental designs (retention testing, choice testing and courtship-initiation testing). The effective odor source can be either the presence of the spider or the presence of the spider’s draglines alone.

This is a preview of subscription content, access via your institution.


Smelling scenery in stereo: Desert ants perceive odor maps in navigation

Scientists of the Max Planck Institute for Chemical Ecology in Jena have investigated another navigational skill of desert ants. These ants are already well-known for their remarkable visual orientation: they use a sun compass along with a step counter and visible landmarks to locate their nest after foraging for food. After the research team from Jena recently discovered that these ants also use olfactory cues to pinpoint their nests, they conducted new experiments: they revealed that the animals can not only locate an odour source, but also use the distribution of different odours in the vicinity of their nests in a map-like manner. The scientists found that the ants need both their antennae for this odour-guided navigation: they smell the scenery in stereo.

The research is published in the journal Animal Behaviour.

The desert ant Cataglyphis fortis is an insect native to the inhospitable salt-pans of Tunisia. To pinpoint the nest -- a tiny hole in the desert ground -- after foraging for food, Cataglyphis combines several navigation systems: a sun compass, a path integrator (the ant literally counts its steps), and visual recognition of landmarks.

Recently, Kathrin Steck, Bill Hansson and Markus Knaden, neuroethologists at the Max Planck Institute for Chemical Ecology in Jena, discovered that local odours also play an important role in the insect's orientation (Frontiers in Zoology, 2009, Vol. 6 No. 5): ants learn to associate a smell with their nest and distinguish this smell from others. But the researchers wanted to know if the insects are also able to recognize odour patterns that emerge, when several odour sources are located at different positions around the nest. And if so, they asked, do ants need both their antennae like stereo receivers just as we employ two eyes and two ears for spatial perception?

"We conducted two key experiments," says Kathrin Steck, PhD student at the institute. "First we marked four odour sources surrounding the nest entrance with the substances methyl salicylate, decanal, nonanal, and indole, and got the ants trained on them. If these four odour points were shifted away from the nest in the original arrangement, the ants repeatedly headed for the odours, even though the nest wasn't there anymore. If we rearranged the odour sources relative to each other, the ants were completely confused."

Therefore the researchers assumed that ants do not "think" one-dimensionally -- i.e. they do not associate the nest with only one smell -- but multi-dimensionally, i.e., they relate an odour landscape to their nest. The odour landscape comprising the four substances was monitored with the help of a special measuring technique: the scientists used a specific photoionisation detector to determine the distribution of the odour substances in space and time.

Spatial perception can easily be acquired if two separate sensory organs are available, such as two eyes for visual orientation. In the case of the ants, this would be their two antennae. "With this assumption, the second key experiment seemed obvious: We tested ants that only had one antenna," Markus Knaden, the leader of the study, explains. In fact, ants with only one sensory device were unable to make use of the odour landscape for navigation.

Stereo smelling in animals is not new -- rats and humans are thought to have this ability as well. This new study shows that ants smell in stereo, but not only that: "In our experiments we demonstrated that ants successfully use stereo smelling for navigation in the desert," says Bill Hansson, director at the institute.