Abstract: Quality-space theory (QST) explains the nature of the mental qualities distinctive of perceptual states by appeal to their role in perceiving. QST is typically described in terms of the mental qualities that pertain to color. Here we apply QST to the olfactory modalities. Olfaction is in various respects more complex than vision, and so provides a useful test case for QST. To determine whether QST can deal with the challenges olfaction presents, we show how a quality space (QS) could be constructed relying on olfactory perceptible properties and the olfactory mental qualities then defined by appeal to that QS of olfactory perceptible properties. We also consider how to delimit the olfactory QS from other modalities. We further apply QST to the role that experience plays in refining our olfactory discriminative abilities and the occurrence of olfactory mental qualities in non-conscious olfactory states. QST is shown to be fully applicable to and useful for understanding the complex domain of olfaction.

Abstract: Decreased olfactory function is very common in the older population, being present in over half of those between the ages of 65 and 80 years and in over three quarters of those over the age of 80 years. Such dysfunction significantly influences physical well-being and quality of life, nutrition, the enjoyment of food, as well as everyday safety. Indeed a disproportionate number of the elderly die in accident gas poisonings each year. As described in this review, multiple factors contribute to such age-related loss, including altered nasal engorgement, increased propensity for nasal disease, cumulative damage to the olfactory epithelium from viral and other environmental insults, decrements in mucosal metabolizing enzymes, ossification of cribriform plate foramina, loss of selectivity of receptor cells to odorants, changes in neurotransmitter and neuromodulator systems, and neuronal expression of aberrant proteins associated with neurodegenerative disease. It is now well established that decreased smell loss can be an early sign of such neurodegenerative diseases as Alzheimer's disease and sporadic Parkinson's disease. In this review we provide an overview of the anatomy and physiology of the aging olfactory system, how this system is clinically evaluated, and the multiple pathophysiological factors that are associated with its dysfunction.

Abstract: Objectives/Hypothesis: The aim of this study was to evaluate the effects of olfactory training (OT) on olfactory function in patients with persistent postinfectious olfactory dysfunction (PIOD). Study Design: Randomized, single-blind, controlled, multicenter crossover study. Methods: Twelve tertiary university medical centers participated. Investigations were performed at three visits (base- line, after 18 weeks, and after 36 weeks), including only subjects with PIOD of <24-months duration. At each visit, partici- pants received detailed assessment of olfactory function. Seventy subjects trained with high concentrations of four odors for 18 weeks; the other half (n 5 74) trained with low concentrations of odors. For the following 18 weeks this regimen was switched. Results: After 18 weeks, olfactory function improved in the high-training group in 18 of 70 participants (26%), whereas only 11/74 improved in the low-training group (15%). In subjects with a duration of olfactory dysfunction of <12 months, olfactory function improved in 15/24 participants (63%) of the high-training group and in 6/31 participants (19%) of the low-training group (P 5.03). Conclusions: OT improves PIOD, and the use of odors at higher concentrations is beneficial to improvement. OT is a safe procedure and appears to be particularly useful in patients who start OT within 12 months after the onset of the disor- der. OT is the first successful therapy regime in patients with PIOD.

Abstract: The function of the CA2 region of the hippocampus is poorly understood. Although the CA1 and CA3 regions have been extensively studied, for years the CA2 region has primarily been viewed as a linking area between the two. However, the CA2 region is known to have distinct neurochemical and structural features that are different from the other parts of the hippocampus and in recent years it has been suggested that the CA2 region may play a role in the formation and/or recall of olfactory-based memories needed for normal social behavior. Although this hypothesis has been supported by hippocampal lesion studies that have included the CA2 region, no studies have attempted to specifically lesion the CA2 region of the hippocampus in mice to determine the effects on social recognition memory and olfaction. To fill this knowledge gap, we sought to perform excitotoxic N-methyl-D-aspartate lesions of the CA2 region and determine the effects on social recognition memory. We predicted that lesions of the CA2 region would impair social recognition memory. We then went on to test olfaction in CA2-lesioned mice, as social memory requires a functional olfactory system. Consistent with our prediction, we found that CA2-lesioned animals had impaired social recognition. These findings are significant because they confirmed that the CA2 region of the hippocampus is a part of the neural circuitry that regulates social recognition memory, which may have implications for our understanding of the neural regulation of social behavior across species.

Abstract: How is sensory information represented in the brain? A long-standing debate in neural coding is whether and how timing of spikes conveys information to downstream neurons. Although we know that neurons in the olfactory bulb (OB) exhibit rich temporal dynamics, the functional relevance of temporal coding remains hotly debated. Recent recording experiments in awake behaving animals have elucidated highly organized temporal structures of activity in the OB. In addition, the analysis of neural circuits in the piriform cortex (PC) demonstrated the importance of not only OB afferent inputs but also intrinsic PC neural circuits in shaping odor responses. Furthermore, new experiments involving stimulation of the OB with specific temporal patterns allowed for testing the relevance of temporal codes. Together, these studies suggest that the relative timing of neuronal activity in the OB conveys odor information and that neural circuits in the PC possess various mechanisms to decode temporal patterns of OB input.

Abstract: In applied olfactory cognition the effects that olfactory stimulation can have on (human) behavior are investigated. To enable an efficient application of olfactory stimuli a model of how they may lead to a change in behavior is proposed. To this end we use the concept of olfactory priming. Olfactory priming may prompt a special view on priming as the olfactory sense has some unique properties which make odors special types of primes. Examples of such properties are the ability of odors to influence our behavior outside of awareness, to lead to strong affective evaluations, to evoke specific memories, and to associate easily and quickly to other environmental stimuli. Opportunities and limitations for using odors as primes are related to these properties, and alternative explanations for reported findings are offered. Implications for olfactory semantic, construal, behavior and goal priming are given based on a brief overview of the priming literature from social psychology and from olfactory perception science. We end by formulating recommendations and ideas for a future research agenda and applications for olfactory priming.

Abstract: Many insect vectors of disease detect their hosts through olfactory cues, and thus it is of great interest to understand better how odors are encoded. However, little is known about the molecular underpinnings that support the unique function of coeloconic sensilla, an ancient and conserved class of sensilla that detect amines and acids, including components of human odor that are cues for many insect vectors. Here, we generate antennal transcriptome databases both for wild type Drosophila and for a mutant that lacks coeloconic sensilla. We use these resources to identify genes whose expression is highly enriched in coeloconic sensilla, including many genes not previously implicated in olfaction. Among them, we identify an ammonium transporter gene that is essential for ammonia responses in a class of coeloconic olfactory receptor neurons (ORNs), but is not required for responses to other odorants. Surprisingly, the transporter is not expressed in ORNs, but rather in neighboring auxiliary cells. Thus, our data reveal an unexpected non-cell autonomous role for a component that is essential to the olfactory response to ammonia. The defective response observed in a Drosophila mutant of this gene is rescued by its Anopheles ortholog, and orthologs are found in virtually all insect species examined, suggesting that its role is conserved. Taken together, our results provide a quantitative analysis of gene expression in the primary olfactory organ of Drosophila, identify molecular components of an ancient class of olfactory sensilla, and reveal that auxiliary cells, and not simply ORNs, play an essential role in the coding of an odor that is a critical host cue for many insect vectors of human disease.

Abstract: Sensory systems encode both the static quality of a stimulus (e.g., color or shape) and its kinetics (e.g., speed and direction). The limits with which stimulus kinetics can be resolved are well understood in vision, audition, and somatosensation. However, the maximum temporal resolution of olfactory systems has not been accurately determined. Here, we probe the limits of temporal resolution in insect olfaction by delivering high frequency odor pulses and measuring sensory responses in the antennae. We show that transduction times and pulse tracking capabilities of olfactory receptor neurons are faster than previously reported. Once an odorant arrives at the boundary layer of the antenna, odor transduction can occur within less than 2 ms and fluctuating odor stimuli can be resolved at frequencies more than 100 Hz. Thus, insect olfactory receptor neurons can track stimuli of very short duration, as occur when their antennae encounter narrow filaments in an odor plume. These results provide a new upper bound to the kinetics of odor tracking in insect olfactory receptor neurons and to the latency of initial transduction events in olfaction.

Abstract: Chemoreception is based on the senses of smell and taste that are crucial for animals to find new food sources, shelter, and mates. The initial step in olfaction involves the translocation of odorants from the periphery through the aqueous lymph of the olfactory sensilla to the odorant receptors most likely by chemosensory proteins (CSPs) or odorant binding proteins (OBPs). To better understand the roles of CSPs and OBPs in a coleopteran pest species, the red flour beetle Tribolium castaneum (Coleoptera, Tenebrionidae), we performed transcriptome analyses of male and female antennae, heads, mouthparts, legs, and bodies, which revealed that all 20 CSPs and 49 of the 50 previously annotated OBPs are transcribed. Only six of the 20 CSP are significantly transcriptionally enriched in the main chemosensory tissues (antenna and/or mouthparts), whereas of the OBPs all eight members of the antenna binding proteins II (ABPII) subgroup, 18 of the 20 classic OBP subgroup, the C + OBP, and only five of the 21 C-OBPs show increased chemosensory tissue expression. By MALDI-TOF-TOF MS protein fingerprinting, we confirmed three CSPs, four ABPIIs, three classic OBPs, and four C-OBPs in the antennae. Most of the classic OBPs and all ABPIIs are likely involved in chemoreception. A few are also present in other tissues such as odoriferous glands and testes and may be involved in release or transfer of chemical signals. The majority of the CSPs as well as the C-OBPs are not enriched in antennae or mouthparts, suggesting a more general role in the transport of hydrophobic molecules.

Abstract: Odor perception is hypothesized to be an experience-dependent process involving the encoding of odor objects by distributed olfactory cortical ensembles. Olfactory cortical neurons coactivated by a specific pattern of odorant evoked input become linked through association fiber synaptic plasticity, creating a template of the familiar odor. In this way, experience and memory play an important role in odor perception and discrimination. In other systems, memory consolidation occurs partially via slow-wave sleep (SWS)-dependent replay of activity patterns originally evoked during waking. SWS is ideal for replay given hyporesponsive sensory systems, and thus reduced interference. Here, using artificial patterns of olfactory bulb stimulation in a fear conditioning procedure in the rat, we tested the effects of imposed post-training replay during SWS and waking on strength and precision of pattern memory. The results show that imposed replay during post-training SWS enhanced the subsequent strength of memory, whereas the identical replay during waking induced extinction. The magnitude of this enhancement was dependent on the timing of imposed replay relative to cortical sharp-waves. Imposed SWS replay of stimuli, which differed from the conditioned stimulus, did not affect conditioned stimulus memory strength but induced generalization of the fear memory to novel artificial patterns. Finally, post-training disruption of piriform cortex intracortical association fiber synapses, hypothesized to be critical for experience-dependent odor coding, also impaired subsequent memory precision but not strength. These results suggest that SWS replay in the olfactory cortex enhances memory consolidation, and that memory precision is dependent on the fidelity of that replay.

Abstract: Autobiographical memories (AMs) are personally experienced events that may be localized in time and space. In the present work we present an overview targeting memories evoked by the sense of smell. Overall, research indicates that autobiographical odor memory is different than memories evoked by our primary sensory systems; sight, and hearing. Here, observed differences from a behavioral and neuroanatomical perspective are presented. The key features of an olfactory evoked AM may be referred to the LOVER acronym-Limbic, Old, Vivid, Emotional, and Rare.

Abstract: The importance of odorants in human life has long been recognized. Literature contains different approaches of physiological and psychological effects of odorant compounds, fragrances and essential oils. This work discusses odorants inhalation effect, based on an overview of major studies in humans. Beneficial effect of fragrances is mainly related to human behaviour. Studies document odorants influence in sympathetic and parasympathetic nervous systems, and neurophysiological brain activity. Moreover, odours compounds can act on the neuroendocrine system, neurotransmitters and neuromodulators, influencing psychological behaviour as well as body function. Odorant inhalation modulates physiological pathways, and in some cases, results in skin function regulation. The mechanism is incompletely elucidated. These findings suggest that olfactory system plays a role in central nervous system function beyond that of smell. In this overview, it was observed that odour compounds influenced stress biomarkers, dehydroepiandrosterone, oxidative stress, estradiol, dopamine, cutaneous barrier, sebum secretion and cutaneous immune system in humans. Some can be related with skin function. As the skin is associated with an extensive biochemical cascade and has complex mechanisms, studies have far to go, as there are processes not yet investigated related to skin that may be affected through olfaction. Future researches are needed to further understand and describe the mechanisms of action of physiological effects in fragrance compounds.

Abstract: We examined whether conversion to dementia can be predicted by self-reported olfactory impairment and/or by an inability to identify odors. Common forms of dementia involve an impaired sense of sme ...

Abstract: Importance Normal olfaction provides essential cues to allow early detection and avoidance of potentially hazardous situations. Thus, patients with impaired olfaction may be at increased risk of experiencing certain hazardous events such as cooking or house fires, delayed detection of gas leaks, and exposure to or ingestion of toxic substances. Objective To identify risk factors and potential trends over time in olfactory-related hazardous events in patients with impaired olfactory function. Design, Setting, and Participants Retrospective cohort study of 1047 patients presenting to a university smell and taste clinic between 1983 and 2013. A total of 704 patients had both clinical olfactory testing and a hazard interview and were studied. On the basis of olfactory function testing results, patients were categorized as normosmic (n = 161), mildly hyposmic (n = 99), moderately hyposmic (n = 93), severely hyposmic (n = 142), and anosmic (n = 209). Interventions Patient evaluation including interview, examination, and olfactory testing. Main Outcomes and Measures Incidence of specific olfaction-related hazardous events (ie, burning pots and/or pans, starting a fire while cooking, inability to detect gas leaks, inability to detect smoke, and ingestion of toxic substances or spoiled foods) by degree of olfactory impairment. Results The incidence of having experienced any hazardous event progressively increased with degree of impairment: normosmic (18.0%), mildly hyposmic (22.2%), moderately hyposmic (31.2%), severely hyposmic (32.4%), and anosmic (39.2%). Over 3 decades there was no significant change in the overall incidence of hazardous events. Analysis of demographic data (age, sex, race, smoking status, and etiology) revealed significant differences in the incidence of hazardous events based on age (among 397 patients P P = .009), and race (among 98 African Americans, 41 [41.8%] with hazardous event, vs 134 of 434 whites [30.9%]; P = .04). Conclusions and Relevance Increased level of olfactory impairment portends an increased risk of experiencing a hazardous event. Risk is further impacted by individuals’ age, sex, and race. These results may assist health care practitioners in counseling patients on the risks associated with olfactory impairment.

Abstract: In many neurodegenerative diseases and particularly in Parkinson’s disease, deficits in olfaction are reported to occur early in the disease process and may be a useful behavioral marker for early detection. Earlier detection in neurodegenerative disease is a major goal in the field because this is when neuroprotective therapies have the best potential to be effective. Therefore, in preclinical studies testing novel neuroprotective strategies in rodent models of neurodegenerative disease, olfactory assessment could be highly useful in determining therapeutic potential of compounds and translation to the clinic. In the present study we describe a battery of olfactory assays that are useful in measuring olfactory function in mice. The tests presented in this study were chosen because they measure olfaction abilities in mice related to food odors, social odors, and non-social odors. These tests have proven useful in characterizing novel genetic mouse models of Parkinson’s disease as well as in testing potential disease-modifying therapies.

Abstract: Uridine diphosphate UDP-glycosyltransferases (UGTs) are detoxification enzymes widely distributed within living organisms. They are involved in the biotransformation of various lipophilic endogenous compounds and xenobiotics, including odorants. Several UGTs have been reported in the olfactory organs of mammals and involved in olfactory processing and detoxification within the olfactory mucosa but, in insects, this enzyme family is still poorly studied. Despite recent transcriptomic analyses, the diversity of antennal UGTs in insects has not been investigated. To date, only three UGT cDNAs have been shown to be expressed in insect olfactory organs. In the present study, we report the identification of eleven putative UGTs expressed in the antennae of the model pest insect Spodoptera littoralis. Phylogenetic analysis revealed that these UGTs belong to five different families, highlighting their structural diversity. In addition, two genes, UGT40R3 and UGT46A6, were either specifically expressed or overexpressed in the antennae, suggesting specific roles in this sensory organ. Exposure of male moths to the sex pheromone and to a plant odorant differentially downregulated the transcription levels of these two genes, revealing for the first time the regulation of insect UGTs by odorant exposure. Moreover, the specific antennal gene UGT46A6 was upregulated by insecticide topical application on antennae, suggesting its role in the protection of the olfactory organ towards xenobiotics. This work highlights the structural and functional diversity of UGTs within this highly specialized tissue.

Abstract: The olfactory bulb (OB) is affected early in both Parkinson's (PD) and Alzheimer's disease (AD), evidenced by the presence of disease-specific protein aggregates and an early loss of olfaction. Whereas previous studies showed amoeboid microglia in the classically affected brain regions of PD and AD patients, little was known about such changes in the OB. Using a morphometric approach, a significant increase in amoeboid microglia density within the anterior olfactory nucleus (AON) of AD and PD patients was observed. These amoeboid microglia cells were in close apposition to β-amyloid, hyperphosphorylated tau or α-synuclein deposits, but no uptake of pathological proteins by microglia could be visualized. Subsequent analysis showed (i) no correlation between microglia and α-synuclein (PD), (ii) a positive correlation with β-amyloid (AD), and (iii) a negative correlation with hyperphosphorylated tau (AD). Furthermore, despite the observed pathological alterations in neurite morphology, neuronal loss was not apparent in the AON of both patient groups. Thus, we hypothesize that, in contrast to the classically affected brain regions of AD and PD patients, within the AON rather than neuronal loss, the increased density in amoeboid microglial cells, possibly in combination with neurite pathology, may contribute to functional deficits.

Abstract: In the present work we present an overview of experimental findings corroborating olfactory imagery observations with the visual and auditory modalities. Overall, the results indicate that imagery of olfactory information share many features with those observed in the primary senses although some major differences are evident. One such difference pertains to the considerable individual differences observed, with the majority being unable to reproduce olfactory information in their mind. Here, we highlight factors that are positively related to an olfactory imagery capacity, such as semantic knowledge, perceptual experience, and olfactory interest that may serve as potential moderators of the large individual variation.

Abstract: Male moths locate their mates using species-specific sex pheromones emitted by conspecific females. One striking feature of sex pheromone recognition in males is the high degree of specificity and sensitivity at all levels, from the primary sensory processes to behavior. The silkmoth Bombyx mori is an excellent model insect in which to decipher the underlying mechanisms of sex pheromone recognition due to its simple sex pheromone communication system, where a single pheromone component, bombykol, elicits the full sexual behavior of male moths. Various technical advancements that cover all levels of analysis from molecular to behavioral also allow the systematic analysis of pheromone recognition mechanisms. Sex pheromone signals are detected by pheromone receptors expressed in olfactory receptor neurons in the pheromone-sensitive sensilla trichodea on male antennae. The signals are transmitted to the first olfactory processing center, the antennal lobe (AL), and then are processed further in the higher centers (mushroom body and lateral protocerebrum) to elicit orientation behavior towards females. In recent years, significant progress has been made elucidating the molecular mechanisms underlying the detection of sex pheromones. In addition, extensive studies of the AL and higher centers have provided insights into the neural basis of pheromone processing in the silkmoth brain. This review describes these latest advances, and discusses what these advances have revealed about the mechanisms underlying the specific and sensitive recognition of sex pheromones in the silkmoth.

Abstract: The olfactory system is involved in sensory functions, emotional regulation and memory formation. Olfactory bulbectomy in rat has been employed as an animal model of depression for antidepressant discovery studies for many years. Olfaction is impaired in animals suffering from chronic stress, and patients with clinical depression were reported to have decreased olfactory function. It is believed that the neurobiological bases of depression might include dysfunction in the olfactory system. Further, brain stimulation, including nasal based drug delivery could provide novel therapies for management of depression.

Abstract: To enhance bite force at the canines, feliform carnivorans have short rostra relative to caniform carnivorans. Rostral reduction in feliforms results in less rostrocaudal space for the maxilloturbinals, the complex set of bones involved in conditioning inspired air and conserving water. It is unknown whether the maxilloturbinals might show adaptations to adjust for this loss, such as greater complexity than what is observed in longer snouted caniforms. To understand the impact of rostral shortening on turbinals in feliforms, we used high resolution CT scans to quantify turbinal surface areas (SA) in 16 feliforms and compared them with published data on 20 caniforms. Results indicate that feliforms have reduced maxilloturbinal SA for their body mass relative to caniforms, but comparable fronto-ethmoturbinal SA. However, anterior portions of the ethmoturbinals in feliforms extend forward into the snout and are positioned within the respiratory pathway. When the SA of these anterior ethmoturbinals is added to maxilloturbinal SA to produce an estimated respiratory SA, feliforms and caniforms are similar in respiratory SA. This transfer of ethmoturbinal SA to respiratory function results in feliforms having less estimated olfactory SA relative to caniforms. Previous work on canids found a positive association between olfactory surface area and diet, but this was not found for felids. Results are consistent with feliforms having somewhat reduced olfactory ability relative to caniforms. If confirmed by behavioral data, the relative reduction in olfactory SA in many feliforms may reflect a greater reliance on vision in foraging relative to caniforms. Anat Rec, 297:2065–2079, 2014. © 2014 Wiley Periodicals, Inc.

Abstract: How consciousness is generated by the nervous system remains one of the greatest mysteries in science. Investigators from diverse fields have begun to unravel this puzzle by contrasting conscious and unconscious processes. In this way, it has been revealed that the two kinds of processes differ in terms of the underlying neural events and associated cognitive mechanisms. We propose that, for several reasons, the olfactory system provides a unique portal through which to examine this contrast. For this purpose, the olfactory system is beneficial in terms of its (a) neuroanatomical aspects, (b) phenomenological and cognitive/mechanistic properties, and (c) neurodynamic (e.g., brain oscillations) properties. In this review, we discuss how each of these properties and aspects of the olfactory system can illuminate the contrast between conscious and unconscious processing in the brain. We conclude by delineating the most fruitful avenues of research and by entertaining hypotheses that, in order for an olfactory content to be conscious, that content must participate in a network that is large-scale, both in terms of the neural systems involved and the scope of information integration.

Abstract: The sensing of vapor odorants is highly demanded in the field of life and medical sciences. Although olfactory receptors (ORs) have potentials to recognize volatile organic compounds, the interaction of ORs, chemical vapors, and peptide components in olfactory mucus has yet to be analyzed to develop OR-based sensors. A bioinspired electrophysiology technique is shown to record the response of reconstituted insect ORs to chemical vapors. To mimic the interface between ORs and olfactory mucus, OR expressing spheroids were loaded into a hydrogel microchamber array. A negative extracellular field potential shift of spheroids was successfully observed by the stimulation of their vapor cognate ligand. Importantly, the ligand repertoire of the OR of malaria vector mosquito examined by this method differed from that of in vivo studies. Our method is useful to develop protein-based gas sensing techniques and to examine the binding of ORs and chemical vapors.

Abstract: The piriform cortex (PCX) is the largest component of the olfactory cortex and is hypothesized to be the locus of odor object formation. The distributed odorant representation found in PCX contrasts sharply with the topographical representation seen in other primary sensory cortices, making it difficult to test this view. Recent work in PCX has focused on functional characteristics of these distributed afferent and association fiber systems. However, information regarding the efferent projections of PCX and how those may be involved in odor representation and object recognition has been largely ignored. To investigate this aspect of PCX, we have used the efferent pathway from mouse PCX to the orbitofrontal cortex (OFC). Using double fluorescent retrograde tracing, we identified the output neurons (OPNs) of the PCX that project to two subdivisions of the OFC, the agranular insula and the lateral orbitofrontal cortex (AI-OPNs and LO-OPNs, respectively). We found that both AI-OPNs and LO-OPNs showed a distinct spatial topography within the PCX and fewer than 10% projected to both the AI and the LO as judged by double-labeling. These data revealed that the efferent component of the PCX may be topographically organized. Further, these data suggest a model for functional organization of the PCX in which the OPNs are grouped into parallel output circuits that provide olfactory information to different higher centers. The distributed afferent input from the olfactory bulb and the local PCX association circuits would then ensure a complete olfactory representation, pattern recognition capability, and neuroplasticity in each efferent circuit.

Abstract: The olfactory recess – a blind pocket at the back of the nasal airway – is thought to play an important role in mammalian olfaction by sequestering air outside of the main airstream, thus giving odorants time to re-circulate. Several studies have shown that species with large olfactory recesses tend to have a well-developed sense of smell. However, no study has investigated how the size of the olfactory recess relates to air circulation near the olfactory epithelium. Here we used a computer model of the nasal cavity from a bat (Carollia perspicillata) to test the hypothesis that a larger olfactory recess improves olfactory airflow. We predicted that during inhalation, models with an enlarged olfactory recess would have slower rates of flow through the olfactory region (i.e. the olfactory recess plus airspace around the olfactory epithelium), while during exhalation these models would have little to no flow through the olfactory recess. To test these predictions, we experimentally modified the size of the olfactory recess while holding the rest of the morphology constant. During inhalation, we found that an enlarged olfactory recess resulted in lower rates of flow in the olfactory region. Upon exhalation, air flowed through the olfactory recess at a lower rate in the model with an enlarged olfactory recess. Taken together, these results indicate that an enlarged olfactory recess improves olfactory airflow during both inhalation and exhalation. These findings add to our growing understanding of how the morphology of the nasal cavity may relate to function in this understudied region of the skull.

Abstract: Recent evidence suggests that humans can become fearful after exposure to olfactory fear signals, yet these studies have reported the effects of fear chemosignals without examining emotion-relevant input from traditional communication modalities (i.e., vision, audition). The question that we pursued here was therefore: How significant is an olfactory fear signal in the broader context of audiovisual input that either confirms or contradicts olfactory information? To test this, we manipulated olfactory (fear, no fear) and audiovisual (fear, no fear) information and demonstrated that olfactory fear signals were as potent as audiovisual fear signals in eliciting a fearful facial expression. Irrespective of confirmatory or contradictory audiovisual information, olfactory fear signals produced by senders induced fear in receivers outside of conscious access. These findings run counter to traditional views that emotions are communicated exclusively via visual and linguistic channels.

Abstract: The importance of chemosensation for vertebrates is reflected in the vast and variable nature of their chemosensory tissues, neurons, and genes, which we explore in this review. Immense progress has been made in elucidating the molecular biology of olfaction since the discovery of the olfactory receptor genes by Buck and Axel, which eventually won the authors the Nobel Prize. In particular, research linking odor ligands to olfactory receptors (ORs) is truly revolutionizing our understanding of how a large but limited number of chemosensory receptors can allow us to perceive the massive diversity of odors in our habitat. This research is providing insight into the evolution of genomes and providing the raw data needed to explore links between genotype and phenotype, still a grand challenge in biology. Research into olfaction is still developing and will no doubt continue until we have a clear understanding of how all odors are detected and the evolutionary forces that have molded the chemosensory subgenome in vertebrates. This knowledge will not only be a huge step in elucidating olfactory function, advancing scientific knowledge and techniques, but there are also commercial applications for this research. This review focuses on the molecular basis of chemosensation, particularly olfaction, its evolution across vertebrates and the recent molecular advances linking odors to their cognate receptors. Anat Rec, 297:2216–2226, 2014. © 2014 Wiley Periodicals, Inc.