Conditioned Odor Research Articles

Impact of olfactory priming on mental representations of food concepts and subsequent food choice

Previous research suggests that food odors act as a prime and influence food choice outside of awareness. Little is known about how odors prime (healthy) food choices. We hypothesized that odors could activate mental representations of food concepts, interacting with cognitive processes underlying food decision-making. We tested this by examining which concepts (healthy, sensory, or product-specific) are activated by odors and how this impacts subsequent food choices. In a between-subjects design, 112 participants were divided into three conditions: healthy odor (apple or banana), unhealthy odor (chocolate or caramel), and non-odor (control). Participants were exposed to one condition for 5 min and then completed a lexical decision task and a screen-based food choice task. The lexical decision task included four word categories: healthy-related, sensory-related, neutral words, and non-words. Reaction times were recorded and computed for each category. Participants were asked to choose one food they wanted to eat from four (in-)congruent food word options and repeated it four times (one for each odor). Results showed participants responded slower to non-words than other words, and slower to healthy and sensory words than neutral words. However, odor exposure did not influence reaction times, nor did the interaction between odor condition and word category affect reaction times. Participants were more likely to choose unhealthy foods regardless of odor exposure. Thus, ambient sweet odors did not prime food-related information or choice. We recommend additional testing using a broader range of odors and word categories to fully validate the association of an odor with a concept.

Sniffing out a solution: How emotional body odors can improve mindfulness therapy for social anxiety

BackgroundHuman body odors (BOs) serve as an effective means of social communication, with individuals exposed to emotional BOs experiencing a partial replication of the sender's affective state. This phenomenon may be particularly relevant in conditions where social interactions are impaired, such as social anxiety. Our study aimed to investigate if emotional human BOs could augment the benefits of mindfulness-based interventions. MethodsWe enrolled 48 women with social anxiety symptoms and assigned them to groups exposed to happiness BO, fear BO, or clean air. Participants engaged in mindfulness practice over two consecutive days, which included breathing, meditation, and relaxation exercises. During these interventions, the odor specific to each group was presented. Affective symptoms were assessed at the beginning and end of each day, with heart rate variability (HRV) and skin conductance level (SCL) recorded during the intervention. ResultsSelf-reported anxiety level revealed a significant reduction in anxiety on the second day for both happiness and fear conditions, but not for the clean air group. However, on a physiological level, fear BO exposure compared to clean air led to decreased HRV, indicating that fear BO may induce a less physiological relaxed state. No significant differences were observed in SCL between odor conditions. ConclusionsThese findings suggest that exposure to BOs triggers the perception of a “social presence”, improving the ecological validity of a psychological treatment. If replicated and expanded, these findings could pave the way for using BOs as catalysts in existing therapies.

Odor-Cued Grab Air Sampling for Improved Investigative Odorant Prioritization Assessment of Transient Downwind Environmental Odor Events.

A critical prelude to any community odor assessment should be the prioritization of specific chemical odorants that are most responsible for targeted downwind odors. Unfortunately, and historically, this is a step that has often been bypassed or overlooked. However, correct understanding of the specific impactful volatile organic compounds (VOCs) can inform the follow-on sampling, analytical, and remediation strategies that are most appropriate and efficient, based upon the chemistry behind the issue. With this understanding, the techniques and sampling strategies presented herein should be viewed as a qualitative prelude rather than an addendum to a follow-up routine, automated downwind odor monitoring. Downwind odor characteristics can vary depending upon the size of the upwind source, interim topography, and wind conditions. At one extreme, the downwind odor plume from a relatively large source located on a flat open plain and under stable, near-straight line wind conditions can be rather broad, sustained, and predictable. In contrast, the plume from a small point source (e.g., a roof vent stack) located on irregular topography and under rapidly shifting wind conditions can be intermittent and fleeting ("spikes" or "bursts"). These transient odor events can be surprisingly intense and offensive, despite their fleeting occurrence and perception. This work reports on improving and optimizing an environmental sampling strategy for odorant prioritization from such transient downwind odor conditions. This optimization addresses the challenges of (1) sampling of transient odor "spikes" and (2) prioritizing odors/odorants from multiple, closely colocated point sources under transient event conditions. Prioritizing is defined as identifying the key impactful odorants downwind. Grab air sampling protocol refinement has emerged from actual community environmental odor assessment projects. The challenge of assessing transient odor events has been mitigated by utilizing (a) rapid, odor-cued whole-air grab sampling (i.e., activated by and synchronous with the perceived sensory spikes) into metalized fluorinated ethylene polymer (m-FEP) gas sampling bags; (b) immediate transfer from bags onto solid-phase microextraction (SPME) fibers or sorbent tubes; and (c) maintaining refrigerated storage and shipment conditions between field collection and in-laboratory analysis. Results demonstrated approximately 11-fold increases in target odorant yields for 900 mL air sample capture on sorbent tube transfers from 2 to 3 s "burst" odor event bag captures compared to equivalent direct collections (with sorbent tubes) at the same downwind receptor location but during perceived (stable) odor "lull" periods. An application targeting general odor sampling and point-source differentiation utilizing tracer gases is also presented.

La presencia de cuernos determina el rango social de carneros Dorper

The aim was to determine if the presence of horns on rams defines whether they are high-ranking or low-ranking. Dorper rams (n = 20) were evaluated to determine their social rank (SR), either high (HSR) or low (LSR), under intensive management conditions. Upon SR classification, the morphometric variables horns presence (HP) or absence (HA) and distance between them, the height at the withers, body length, thoracic perimeter, and scrotal circumference, male odor, body weight, and body condition score were registered. Afterward, semen evaluations were performed, recording the ejaculated volume, sperm concentration, and mass motility. There were no differences (p > 0.05) for the morphometric variables between the groups. However, HP as well as semen quality were higher (p < 0.05) in HSR males. The presence of horns in the rams determined their social rank and the dominant males showed better semen quality than the subordinate males.

Canine detection of explosives under adverse environmental conditions with and without acclimation training.

Canines are one of the best biological detectors of energetic materials available; however, canine detection of explosives is impacted by a number of factors, including environmental conditions. The objectives of this study were: 1) determine how canine detection limits vary when both the canine and odorant are tested in varying temperature and humidity conditions (canine and odor interactive effects); and 2) determine if an acclimatization plan can improve detection limits in an adverse environmental condition. Eight working line canines were trained to detect four energetics: prill ammonium nitrate (AN), Composition 4 (C4), trinitrotoluene (TNT) and double base smokeless powder (SP). In Experiment 1, canines completed a 3-alternative forced choice 3-down-1-up staircase threshold assessment in five environmental conditions: 40°C and 70% relative humidity (RH), 40°C and 40% RH, 0°C and 90% RH, 0°C and 50% RH and 21°C and 50% RH. Canines showed a 3.5-fold detection limit increase (poorer detection) for C4 in 40°C and 70% RH compared to their detection limit at 21°C and 50% RH. In Experiment 2, the eight canines were split into two groups (n = 4), control and acclimation groups. The control group completed the threshold assessment for C4 at 21°C and 50% RH each day for 20 days, with 5 minutes of petting prior to testing. The acclimation group completed the same assessment daily starting at 21°C and 50% RH but temperature and RH were incremented daily over the course of 6 days to the 40°C and 70% RH condition. After the initial six days, the acclimation group completed daily assessments at 40°C and 70% RH condition for the remainder of the experiment. All acclimatization group canines started their session with 5 minutes of toy or food retrieves. Detection limits for C4 for all dogs were tested in 40°C and 70% RH on day 11 and day 22. The acclimatization plan improved detection limits in the 40°C and 70% RH condition for C4 compared to the non-acclimated group. In this set of experiments, canine detection limits for four explosive odorants were found to vary based on environmental condition and were mostly driven by impacts on the canine rather than odor availability. The acclimatization plan did result in lower detection limits (i.e., increased performance). Future work should determine what factor (exercise or environmental exposure) is more effective in acclimatization for odor detection work.

Technology development and study of properties of craft marshmallows with raspberry puree

The development of recipes with natural raw materials enriched with bioactive substances is an urgent task for providing the population with a complete and balanced diet. The aim of the study is to develop recipes of craft marshmallows for therapeutic, prophylactic and health-improving purposes. The research was conducted by means of the expert method, sensory analysis, and statistical methods of processing experimental data. Standard and generally accepted methods were used to determine physical and chemical parameters. To achieve this goal, it is proposed to replace part of the apple puree in the recipe with raspberry because of the raspberries’ antibacterial and immunomodulatory properties. Models of marshmallow composition with different proportions of apple and raspberry puree, protein, sugar, glucose syrup and agar-agar were developed. The sensory analysis was carried out and the organoleptic characteristics of model marshmallow compositions (taste, odour, colour, consistency, structure, and surface condition) were determined. A sensory profilogram for model marshmallow compositions was created and the model composition with the best organoleptic characteristics was determined on the basis of the expert evaluation results. The content of pectin substances and L-ascorbic acid in the studied samples was determined. The physical and chemical parameters for the model marshmallow compositions were determined. It was found that due to the increase of raspberry puree content in the marshmallow recipe the moisture content of the marshmallow will increase from 21.3% ± 0.3% in MC1 with 30% raspberry puree content to 22.1% ± 0.3% in MC3 with 40% raspberry puree content. The density, active and titratable acidity of the marshmallow will decrease with the increase of raspberry puree amount in it. The expediency of using vitamin and pectin-containing raw materials (such as raspberry puree) for therapeutic, prophylactic and health-improving purposes in the marshmallow production technology has been experimentally proved. The marshmallow recipes with different proportions of apple and raspberry puree, possessing therapeutic, preventive and health-improving purposes and expanding the range of sugary confectionery products have been developed. The proposed marshmallows contain natural ingredients and are characterised by high organoleptic characteristics. Marshmallows on the developed recipes can be produced on confectionery production line of various capacities and in restaurant establishments

Air quality in the car: How CO2 and body odor affect drivers' cognition and driving performance?

Elevated indoor levels of CO2 and the presence of body odor have been shown to have adverse effects on the cognitive function of building occupants. These factors may also contribute to impaired in-car driving performance, potentially posing a threat to transportation and public safety. To investigate the effects of CO2 and body odor on driving performance, we enrolled 25 participants in highway driving tasks under three indoor CO2 levels (800, 1800, and 3500 ppm) and two body odor conditions (presence and absence). CO2 was injected in the cabin to increase CO2 levels. In addition, we assessed working memory and reaction time using N-back tasks during driving. We found that driving speed, acceleration, and lateral control were not significantly affected by either CO2 or body odor. We observed no significant differences in sleepiness or emotion under varying CO2 or body odor conditions, except for a lower level of emotion valence with exposure to body odor. Task load was also not significantly impacted by CO2 or body odor levels, except for a higher reported effort at 1800 ppm compared to 800 ppm CO2. However, participants did demonstrate significantly higher accuracy with increased body odor exposure, suggesting a complex effect of volatile organic compounds on driver cognition. Our findings also revealed moderating effects of task difficulty of N-back tests and exposure duration on cognition and driving performance. This is one of the first few in-depth studies regarding environmental factors and their effect on drivers' cognition and driving performance, and these results provide valuable insights for car-cabin environmental design for air quality and driving safety.

Effects of reproductive status on behavioral and neural responses to isolated pup stimuli in female California mice

The transition to motherhood in mammals is marked by changes in females’ perception of and responsiveness to sensory stimuli from infants. Our understanding of maternally induced sensory plasticity relies most heavily on studies in uniparental, promiscuous house mice and rats, which may not be representative of rodent species with different life histories. We exposed biparental, monogamous California mouse (Peromyscus californicus) mothers and ovariectomized virgin females to one of four acoustic and olfactory stimulus combinations (Control: clean cotton and white noise; Call: clean cotton and pup vocalizations; Odor: pup-scented cotton and white noise; Call + Odor: pup-scented cotton and pup vocalizations) and quantified females’ behavior and Fos expression in select brain regions. Behavior did not differ between mothers and ovariectomized virgins. Among mothers, however, those exposed to the Control condition took the longest to sniff the odor stimulus, and mothers exposed to the Odor condition were quicker to sniff the odor ball compared to those in the Call condition. Behavior did not differ among ovariectomized virgins exposed to the different conditions. Fos expression differed across conditions only in the anterior hypothalamic nucleus (AHN), which responds to aversive stimuli: among mothers, the Control condition elicited the highest AHN Fos and Call + Odor elicited the lowest. Among ovariectomized virgin females, Call elicited the lowest Fos in the AHN. Thus, reproductive status in California mice alters females’ behavioral responses to stimuli from pups, especially odors, and results in the inhibition of defense circuitry in response to pup stimuli.

Relaxing and stimulating ambient odors influence preferences for musical tempo

It has recently been shown that relaxing and stimulating odors distort time perception by slowing down or speeding up the pacemaker of the internal clock. Since individuals tend to prefer musical tempo at the rate of the pacemaker, we examined whether relaxing and stimulating ambient odors could bias tempo preference in a study in which the musical stimuli were unfamiliar pleasant musical excerpts. Participants listened to pairs of excerpts played at slightly different tempi and had to indicate which one they preferred. We hypothesized that participants exposed to a relaxing odor (strawberry) would prefer the slower excerpts while participants exposed to a stimulating odor (lemon) would prefer the faster excerpts. As expected, the findings showed that participants in the control (no odor) condition preferred the slower of the fast-tempo pairs of excerpts and the faster of the slow-tempo pairs, indicating a preference bias for moderate tempo. Preferences in both odor conditions differed significantly from those in the control condition such that no such preference bias was observed. There was an interaction between tempo and odor such that participants showed no preference for the slower of the fast-tempo pairs of excerpts in the presence of a lemon odor, and no preference for the faster of the slow-tempo pairs in the presence of a strawberry odor. To our knowledge, this is the first time it has been shown that odors can alter the rate of the pacemaker without participants being conscious of the presence of an olfactory stimulus in the environment.

Negative valence encoding in the lateral entorhinal cortex during aversive olfactory learning

Olfactory learning is widely regarded as a substrate for animal survival. The exact brain areas involved in olfactory learning and how they function at various stages during learning remain elusive. Here, we investigate the role of the lateral entorhinal cortex (LEC) and the posterior piriform cortex (PPC), two important olfactory areas, in aversive olfactory learning. We find that the LEC is involved in the acquisition of negative odor value during olfactory fear conditioning, whereas the PPC is involved in the memory-retrieval phase. Furthermore, inhibition of LEC CaMKIIα+ neurons affects fear encoding, fear memory recall, and PPC responses to a conditioned odor. These findings provide direct evidence for the involvement of LEC CaMKIIα+ neurons in negative valence encoding.

Time-Dependent Analysis of Human Neurophysiological Activities during an Ecological Olfactory Experience.

It has been demonstrated that odors could affect humans at the psychophysiological level. Significant research has been done on odor perception and physiological mechanisms; however, this research was mainly performed in highly controlled conditions in order to highlight the perceptive phenomena and the correlated physiological responses in the time frame of milliseconds. The present study explored how human physiological activity evolves in response to different odor conditions during an ecological olfactory experience on a broader time scale (from 1 to 90 s). Two odors, vanilla and menthol, together with a control condition (blank) were employed as stimuli. Electroencephalographic (EEG) activity in four frequency bands of interest, theta, alpha, low beta, and high beta, and the electrodermal activity (EDA) of the skin conductance level and response (SCL and SCR) were investigated at five time points taken during: (i) the first ten seconds of exposure (short-term analysis) and (ii) throughout the entire exposure to each odor (90 s, long-term analysis). The results revealed significant interactions between the odor conditions and the time periods in the short-term analysis for the overall frontal activity in the theta (p = 0.03), alpha (p = 0.005), and low beta (p = 0.0067) bands, the frontal midline activity in the alpha (p = 0.015) and low beta (p = 0.02) bands, and the SCR component (p = 0.024). For the long-term effects, instead, only one EEG parameter, frontal alpha asymmetry, was significantly sensitive to the considered dimensions (p = 0.037). In conclusion, the present research determined the physiological response to different odor conditions, also demonstrating the sensitivity of the employed parameters in characterizing the dynamic of such response during the time. As an exploratory study, this work points out the relevance of considering the effects of continuous exposure instead of short stimulation when evaluating the human olfactory experience, providing insights for future studies in the field.

Behavioral responses of horses (Equus ferus caballus) vary in response to potentially threatening odor condition and aversive social odor stimuli

Horses (Equus ferus caballus) engage their sense of smell in numerous behaviors. However, only few studies so far evaluated responses of horses to olfactory stimuli presumed to be either attractive or aversive and rather focused on presenting horses with only one type of odor. Therefore, we assessed behavioral responses of horses towards seven natural odors that are either potentially threatening, or socially attractive, or socially aversive. To this end, we presented a total of 10 horses with the following odors: same-sex and opposite-sex horse feces; same-sex and opposite-sex horse urine; tiger (Panthera tigris) feces and urine; and horse blood attached to one of two simultaneously presented food buckets and recorded their behavior. We found that the horses displayed clear behavioral reactions towards potentially threatening odors (tiger feces and urine; horse blood) compared to socially attractive (opposite-sex feces and urine) and, in some cases, socially aversive (same-sex feces and urine) odors. More precisely, the horses put their ears back significantly more frequently and tended to do it for longer in the potentially threatening odor condition compared to the socially attractive one. In the potentially threatening odor condition, the horses ate from the control bucket significantly more frequently compared to the other two conditions. Detailed analyses showed that the horses’ behavioral responses were particularly pronounced following exposure to tiger feces and urine. Furthermore, we found that, in some situations, socially aversive odor stimuli caused higher vigilance and more cautious approach, as reflected in increased time of sniffing the odor-bearing bucket and decreased frequency of eating from it in the socially aversive compared to the potentially threatening odor condition. These findings suggest that horses, which are known as prey and social animals, are sensitive to social odors and even more so to odors from predators.

Odours in a visual virtual environment: effects of congruency

ABSTRACT The present study aimed to explore the effects of odours, presented together with a virtual reality (V.R.) environment, on memory and numerous aspects of perception in the context of congruency vs incongruency. We examined both effects of intended manipulation of congruency (determined by a group of olfactory experts) and the manipulation check (individual perception of congruency) between V.R. environment and olfactory conditions. 100 participants watched 5 different pleasant vs unpleasant three-dimensional 360° videos, and were randomly attributed to one of 5 groups, each exposed to a specific pleasant or unpleasant odour condition. Following the presentation of each of the 5 V.R. environments, the participants responded to 9 questions assessing various aspects of each V.R. presentation. During the second test, the participants provided self-declared memory ratings and descriptions of the content of the V.R. scenes without experiencing odours or V.R. environments. Linear Mixed Model analyses revealed that intended manipulation of congruency increased some perceived positive aspects of virtual videos. However, odours that are incongruent with visual contents also enhanced positive assessment of the V.R. environments what was further noticed in case of the manipulation check. Eventually, high level of self-declared memory of virtual videos’ details positively influenced V.R. environments’ perception.

The neural substrates responsible for food odor processing: an activation likelihood estimation meta-analysis.

In many species including humans, food odors appear to play a distinct role when compared with other odors. Despite their functional distinction, the neural substrates responsible for food odor processing remain unclear in humans. This study aimed to identify brain regions involved in food odor processing using activation likelihood estimation (ALE) meta-analysis. We selected olfactory neuroimaging studies conducted with sufficient methodological validity using pleasant odors. We then divided the studies into food and non-food odor conditions. Finally, we performed an ALE meta-analysis for each category and compared the ALE maps of the two categories to identify the neural substrates responsible for food odor processing after minimizing the confounding factor of odor pleasantness. The resultant ALE maps revealed that early olfactory areas are more extensively activated by food than non-food odors. Subsequent contrast analysis identified a cluster in the left putamen as the most likely neural substrate underlying food odor processing. In conclusion, food odor processing is characterized by the functional network involved in olfactory sensorimotor transformation for approaching behaviors to edible odors, such as active sniffing.

Sleep is required to consolidate odor memory and remodel olfactory synapses

Animals with complex nervous systems demand sleep for memory consolidation and synaptic remodeling. Here, we show that, although the Caenorhabditis elegans nervous system has a limited number of neurons, sleep is necessary for both processes. In addition, it is unclear if, in any system, sleep collaborates with experience to alter synapses between specific neurons and whether this ultimately affects behavior. C.elegans neurons have defined connections and well-described contributions to behavior. We show that spaced odor-training and post-training sleep induce long-term memory. Memory consolidation, but not acquisition, requires a pair of interneurons, the AIYs, which play a role in odor-seeking behavior. In worms that consolidate memory, both sleep and odor conditioning are required to diminish inhibitory synaptic connections between the AWC chemosensory neurons and the AIYs. Thus, we demonstrate in a living organism that sleep is required for events immediately after training that drive memory consolidation and alter synaptic structures.

When are puppies receptive to emotion-induced human chemosignals? The cases of fear and happiness

We report an observational, double-blind, experimental study that examines the effects of human emotional odors on puppies between 3 and 6 months and adult dogs (one year and upwards). Both groups were exposed to control, human fear, and happiness odors in a between subjects’ design. The duration of all behaviors directed to the apparatus, the door, the owner, a stranger, and stress behaviors was recorded. A discriminant analysis showed that the fear odor activates consistent behavior patterns for both puppies and adult dogs. However, no behavioral differences between the control and happiness odor conditions were found in the case of puppies. In contrast, adult dogs reveal distinctive patterns for all three odor conditions. We argue that responses to human fear chemosignals systematically influence the behaviors displayed by puppies and adult dogs, which could be genetically prefigured. In contrast, the effects of happiness odors constitute cues that require learning during early socialization processes, which yield consistent patterns only in adulthood.

Environmental and Socio-economic Impact Assessment in Hazaribag Area of Dhaka for Tannery Relocation

Purpose of the study: The objective of this study is to find out the tannery relocation’s impact on the surrounding environment, social, economic, livelihood conditions, and institutional and stakeholder perception in Hazaribag. Methodology: The methodological framework includes a field survey and Participatory Rural Appraisal (PRA) tools, i.e., Focus Group Discussion (FGD) and Key Informant Interview (KII). Main Findings: After the relocation, the surrounding environment, odour, and surface water condition have improved at a very satisfactory rate. Nevertheless, many tannery workers either become unemployed or transferred to their non-expertise field, and the economic and business condition of the area has decreased. Also, there are some conflicts between the owner and workers. After the relocation, the government has not properly managed the post-relocation situation in the brownfield. Research implications/limitations: The research findings will be helpful in planning the utilization of the brownfield. The study's limitations include reliance on respondents' perceptions and opinions and not conducting chemical analysis for water and environmental monitoring. Continuous monitoring of the change is needed to find the impact in the long run. Novelty/Originality of this study: Many studies were conducted on the impact of the Tannery in the Hazaribag area, and the Tannery was eventually relocated. The study fills a gap in the literature by presenting the scenario after the relocation to address the impact of relocation in Hazaribag, which is a significant observation for further development of the brownfield area.

Inhibitory and excitatory alcohol-seeking cues distinct roles in behavior, neurochemistry, and mesolimbic pathway in alcohol preferring (P) rats

Cues associated with alcohol use can readily enhance self-reported cravings for alcohol, which increases the likelihood of reusing alcohol. Understanding the neuronal mechanisms involved in alcohol-seeking behavior is important for developing strategies to treat alcohol use disorder. In all experiments, adult female alcohol-preferring (P) rats were exposed to three conditioned odor cues; CS+ associated with EtOH self-administration, CS- associated with the absence of EtOH (extinction training), and a CS0, a neutral stimulus. The data indicated that presentation of an excitatory conditioned cue (CS+) can enhance EtOH- seeking while the CS- can inhibit EtOH-seeking under multiple test conditions. Presentation of the CS+ activates a subpopulation of dopamine neurons within the interfascicular nucleus of the posterior ventral tegmental area (posterior VTA) and basolateral amygdala (BLA). Pharmacological inactivation of the BLA with GABA agonists inhibits the ability of the CS+ to enhance EtOH-seeking but does not alter context-induced EtOH-seeking or the ability of the CS- to inhibit EtOH-seeking. Presentation of the conditioned odor cues in a non-drug-paired environment indicated that presentation of the CS+ increased dopamine levels in the BLA. In contrast, presentation of the CS- decreased both glutamate and dopamine levels in the BLA. Further analysis revealed that presentation of a CS+ EtOH-associated conditioned cue activates GABA interneurons but not glutamate projection neurons. Overall, the data indicate that excitatory and inhibitory conditioned cues can contrarily alter EtOH-seeking behaviors and that different neurocircuitries are mediating these distinct cues in critical brain regions. Pharmacotherapeutics for craving should inhibit the CS+ and enhance the CS- neurocircuits.

Odor Threshold Differs for Some But Not All Odorants Between Older and Younger Adults.

Olfactory function deteriorates with age, and definitive mechanisms by which this decline occurs are likely multifactorial. The present study, conducted on a large cohort of healthy participants, aimed to investigate whether odor thresholds would differ for variable odors with different physicochemical (e.g., heavy- vs lightweight molecules) and perceptual characteristics. In 81 participants (51%, ≥50 years old), we assessed odor threshold in 2 sessions. Linear mixed-model analyses revealed that odor thresholds in younger and older adults changed with different odor conditions, presumably due to the common exposition to some of the odors, their trigeminality, and lipophilicity. This effect was observed for piperine, eucalyptol, 2-nonanone, gamma-valerolactone, and pinene-alpha, but not for the other 15 odorants studied. Furthermore, suprathreshold perception, that is, intensity and, to some extent, irritation, contributed independently to sensorial odor threshold, the latter ones particularly in older adults. We also found that the molecular weight of the odorants did not add to their threshold by, respectively, younger and older adults. To conclude, the present findings are in line with previous studies showing that the age-related change of chemosensory abilities is a multifaceted phenomenon, which does not affect all odorants.

Relaxing effects of music and odors on physiological recovery after cognitive stress and unexpected absence of multisensory benefit.

Several studies have described, often separately, the relaxing effects of music or odor on the autonomic nervous system (ANS) activity. Only a few studies compared the presentation of these stimuli and their interaction within a same experimental protocol. Here, we examined whether relaxing music (slow-paced classical pieces) and odor (lavender essential oil) either presented in isolation or in combination would facilitate physiological recovery after cognitive stress. We continuously recorded the electrocardiogram to assess the high-frequency component of heart rate variability (HF-HRV), an index of parasympathetic activity, and electrodermal activity (EDA), an index of sympathetic activity, 10min before, during and 30 min after a cognitive stress (i.e., completing timely constrained cognitively demanding tasks) in 99 participants allocated to four recovery conditions (control N=26, music N=23, odor N=24, music+odor N=26). The stressing event triggered both a significant increase in EDA and decrease in HF-HRV (compared to baseline). During the recovery period, the odor elicited a greater decrease in EDA compared to an odorless silent control, whereas no difference in HRV was observed. Conversely, during this period, music elicited a greater increase in HF-HRV compared to control whereas no difference in EDA was observed. Strikingly, in the multimodal music+odor condition, no beneficial effect was observed on ANS indexes 30 min after stress. Overall, our study confirms that both olfactory and musical stimuli have relaxing effects after stress on ANS when presented separately only, which might rely on distinct neural mechanisms and autonomic pathways.