Rapid mood change and human odors

We demonstrate an immediate effect of airborne chemicals on human moods. We collected six groups of underarm odors, respectively, from five prepubertal girls, five prepubertal boys, five college women, five college men, five older women, and five older men. In addition, we collected odors from homes of these donors, making them a seventh group of odor. Three hundred and eight odor observers ranked the seven groups of odors of little girls, little boys, college women, college men, older women, older men, and homes by their perceived pleasantness, intensity, perceived masculinity, and age of the donors, among other qualities. On a separate task, the same odor observers assessed their depressive, hostile, and positive moods twice, once before and once a few minutes after they sniffed one of the above seven groups of odors. Exposure to underarm odors for under 2 min led to significant, rapid, and small changes in the nonclinical depressive mood of the odor observers. The mood changes were independent of the observers' perceptions of odor qualities. Odors perceived as unpleasant and intense were as likely to relieve a depressive mood as were pleasant odors.     

Identification of unpleasant odors is independent of age.

The purpose of this study was to investigate (a) the relationship between identification proficiency for specific odors and chronological age and (b) to determine whether the relationships were related to perceived quality (i.e., judgments of familiarity, intensity, and hedonics) of the odor item. Data from 472 subjects (227 men, 245 women) ranging in age from 18 to 79 years were assessed in a cued identification test comprising 16 odors. The results indicated a reliable age effect in overall odor identification performance. Further analyses indicated that the observed age-related deficit was odorant-specific, with some odors being equally well identified across age cohorts and others showing sensitivity to the process of aging. Additional examination regarding the observed age-differential effects across the different odor types indicated that these may be understood according to the pleasantness/upleasantness associated with the odor. Specifically, odors perceived as unpleasant showed age invariance whereas odors rated as pleasant exhibited age sensitivity.     

Quantitative assessment of olfactory experience during pregnancy.

Results of the National Geographic Smell Survey were used to investigate the effects of pregnancy on olfactory perception and odor-related behavior. The responses to test odors and survey questions of 13,610 pregnant and 277,228 nonpregnant U.S. women between 20 and 40 years of age were analyzed. In comparison to nonpregnant women, pregnant women rated their own sense of smell lower, more often rated the test odors less pleasant smelling, more often classified the test odors as inedible, were less likely to report odor-evoked memories, and used perfume and cologne less frequently. Differences in odor detection and intensity rating did not favor either group.     

Startle reflex modulation during exposure to pleasant and unpleasant odors

The eyeblink component of the startle response to acoustic probes was measured while subjects smelled pleasant odors, unpleasant odors, or no odor. Peak electromyogram (EMG) 20–90 ms after probe onset was greater during unpleasant than during no odor conditions; EMGs for pleasant odors did not differ from those for no odor. Base tension in orbicularis oculi muscles was also higher during unpleasant odors. The results for unpleasant odors parallel those found in previous studies that have used a variety of methods for producing negatively valenced experiences. The results for pleasant odors diverge from those of most previous studies, which have found startle attenuation during positively valenced experiences. However, the results may be compatible with the suggestion (Lang, Bradley, & Cuthbert, 1992) that the motivational state that modulates startle involves both valence and arousal. Pleasant odors may require appropriate contexts to produce the positive motivational state required for startle attenuation.     

Influence of affective and cognitive judgments on autonomic parameters during inhalation of pleasant and unpleasant odors in humans

Hedonic tone is so salient in odor perception that several authors have used odors to induce affective states. Various studies have shown that the electrophysiological and psychophysiological response patterns induced by olfactory stimuli are different for pleasant and unpleasant odors, and that these types of odor activate brain structures differentially. These results suggest that odors are first categorized according to pleasantness. The objective of the present work was to study the possible existence of an involuntary affective categorization in olfaction. Given that certain variations in the autonomic system, such as skin conductance amplitude and heart rate, are not under the voluntary control of human subjects, we used such psychophysiological methods for this investigation. Our results indicate that unpleasant odors provoke heart-rate acceleration during both a smelling task (control condition: a task in which subjects had only to inhale odors) and a pleasantness judgment, but not during a familiarity judgment. These results suggest that subjects involuntarily categorize odors by their pleasantness.     

Respiratory responses to olfactory stimuli in Parkinson's disease

There are many reports of olfactory impairment in patients with Parkinson's disease (PD) and the impairment can be observed before the appearance of typical PD symptom. Accordingly, olfactory screening tests may predict disease onset and indicates a need for early treatment before classic signs of the disease. Olfaction is dependent on inspiration, and activation of olfactory limbic areas are synchronized with the natural breathing cycle in animals and humans. Subconscious changes in respiratory pattern occur in response to odor stimulation. The use of olfactory stimuli to investigate respiratory pattern could be used to assess olfactory perception and serve as an index for olfactory limbic activation. In this study, we tested olfactory acuity in normal subjects and in patients with PD and recorded V(O2) and respiratory variables during pleasant and unpleasant odor presentation. All subjects were able to detect the odorants; however patients with PD were assigned to one of two groups, group that could recognize odors or the group with impaired odor recognition. Respiratory response toward unpleasant and pleasant odor recognition were weak in PD groups who could recognize odors than normal subject as well as emotional response to odor stimuli. PD group with impaired odor recognition showed no respiratory response toward odor stimuli. PD may experience difficulty in feeling positive emotions toward pleasant odors prior to the unpleasant odor because respiratory responses to pleasant odors may also be related to higher processes including intentional control of breathing pattern as a result of olfactory cortex processing and perceptions or emotions.     

Ambient odors of orange and lavender reduce anxiety and improve mood in a dental office

The goal of this study was to investigate the impact of the essential oils of orange and lavender on anxiety, mood, alertness and calmness in dental patients. Two hundred patients between the ages of 18 and 77 years (half women, half men) were assigned to one of four independent groups. While waiting for dental procedures patients were either stimulated with ambient odor of orange or ambient odor of lavender. These conditions were compared to a music condition and a control condition (no odor, no music). Anxiety, mood, alertness and calmness were assessed while patients waited for dental treatment. Statistical analyses revealed that compared to control condition both ambient odors of orange and lavender reduced anxiety and improved mood in patients waiting for dental treatment. These findings support the previous opinion that odors are capable of altering emotional states and may indicate that the use of odors is helpful in reducing anxiety in dental patients.     

A rose by any other name: would it smell as sweet?

We examined whether presenting an odor with a positive, neutral, or negative name would influence how people perceive it. In experiment 1, 40 participants rated 15 odors for their pleasantness, intensity, and arousal. In experiment 2, 30 participants passively smelled 10 odors while their skin conductance (SC), heart rate (HR), and sniffing were recorded. We found significant overall effects of odor names on perceived pleasantness, intensity, and arousal. Pleasantness showed the most robust effect of odor names: the same odors were perceived as more pleasant when presented with positive than with neutral and negative names and when presented with neutral than with negative names. In addition, odorants were rated as more intense when presented with negative than with neutral and positive names and as more arousing when presented with positive than with neutral names. Furthermore, SC and sniff volumes, but not HR, were modified by odor names, and the SC changes could not be accounted for by sniffing changes. Importantly, odor names presented with odorless water did not produce any effect on skin conductance and sniff volumes, ruling out the possibility that the naming-related findings were triggered by an emotional reaction to odor names. Taken together, these experiments show that there is a lot to a name, at least when it comes to olfactory perception.     

Effects of pleasant and unpleasant ambient odors on human voice pitch

The perception of odors is well identified as having strong emotional correlates. It is also well known that the acoustic characteristics of the voice differ according to the emotional state. This study compared some acoustic features of the voice of 18 subjects reading the same text in pleasant (lavender) and unpleasant (pyridine) ambient odor conditions. The results revealed that the pitch of the voice was higher in the pleasant than in the unpleasant condition. These findings are consistent with the hypothesis of local and functional convergences of encoding vocal emotion and hedonic perception of odors.     

Effects of reproductive state on olfactory sensitivity suggest odor specificity

Previous studies of reproductive state and olfactory sensitivity in women have not directly compared thresholds for social and environmental odors. Here, we used successive dilutions presented in a staircase protocol to determine olfactory thresholds for androstadienone, a social odor produced by men, and rose, an environmental odor signaling a source of micronutrients essential for successful implantation, prenatal development and maternal health. Fertile women were more sensitive to the social than the environmental odor, while women using oral contraceptives, a non-fertile hormonal state similar to early pregnancy, were more sensitive to the environmental odor. This preliminary study sets the stage for further work on the interaction between hormonal states and sensitivity to specific odors with reproductive significance.     

Taste modulation of nociception differently affects chronically stressed rats

Stress responses cover a wide range of physiological changes, including alterations in the perception of and response to pain. Animals submitted to repeated stress present altered nociception and this effect is part of this process of adaptation; in addition pleasant and unpleasant experiences with tastes and odors have been shown to affect distinct behavioral aspects, such as pain perception. The aim of the present study is to verify the responses of repeatedly stressed rats (1 h of daily immobilization during 40 days) to pleasant and unpleasant tastes on nociception, when compared to control animals. An increase in the tail-flick latency (TFL) was observed 5 min after exposure to a sweet taste in the control group, whereas no effect was observed in chronically stressed animals. When submitted to an unpleasant taste (5% acetic acid), the chronically stressed group presented an increase in TFL, whereas no effect was observed in the control group. In conclusion, chronically stressed animals present different nociceptive responses to sweet and acid tastes; although control animals suitably respond to a sweet stimulus, stressed animals seem to be more apt to react to the unpleasant stimulus.     

Improved smell pleasantness after odor-taste associative learning in humans

Whereas some aspects of olfactory hedonism in humans are present from birth, others form during development and throughout adulthood. Although it is generally agreed that such hedonic representations emerge by associative learning, it is not yet clear which learning parameters are prominent. The present study investigated the influence of number of trials on odor preference acquisition in human adults. Forty-eight subjects randomly assigned to three groups were tested in three sessions. In the first session, subjects ranked eight food odors from most pleasant to most unpleasant. The second session consisted in an associative learning, the two most neutral odors were randomly associated with a drink: one odor with water (CS-) and the other odor with a pleasant sweet solution (CS+). In the third session subjects ranked the eight food odors again. In group A, CS+ was paired three times with the US, and in group B only once; in group C, CS+ was paired only once with the US but with a total duration identical to that in group A. Results showed that CS+ was ranked as significantly more pleasant after learning in group A (p<.05), but not in groups B and C (p>.05). In conclusion, the study showed that a neutral smell can acquire positive emotional features after being paired with a pleasant taste, and that this learning depends on the number of associations between smell and taste.     

Sedative effects of the jasmine tea odor and (R)-(−)-linalool, one of its major odor components, on autonomic nerve activity and mood states

We investigated the effects of the odor of jasmine tea on autonomic nerve activity and mood states in a total of 24 healthy volunteers. We used the odor of jasmine tea at the lowest concentration that could be detected by each subject but that did not elicit any psychological effects. R–R intervals and the POMS test were measured before and after inhalation of the odors for 5 min. Both jasmine tea and lavender odors at perceived similar intensity caused significant decreases in heart rate and significant increases in spectral integrated values at high-frequency component in comparison with the control (P < 0.05). In the POMS tests, these odors produced calm and vigorous mood states. We also examined the effects of (R)-(–)-linalool, one of its major odor components, at the same concentration as in the tea, and (S)-(+)-linalool. Only (R)-(–)-linalool elicited a significant decrease in heart rate (P < 0.05) and an increase in high-frequency component in comparison with the controls, and produced calm and vigorous mood states. Thus, the low intensity of jasmine tea odor has sedative effects on both autonomic nerve activity and mood states, and (R)-(–)-linalool, one of its components, can mimic these effects.     

Olfactory influences on appetite and satiety in humans

Odor stimuli play a major role in perception of food flavor. Food-related odors have also been shown to increase rated appetite, and induce salivation and release of gastric acid and insulin. However, our ability to identify an odor as food-related, and our liking for food-related odors, are both learned responses. In conditioning studies, repeated experience of odors with sweet and sour tastes result in enhanced ratings of sensory quality of the paired taste for the odor on its own. More recent studies also report increased pleasantness ratings for odors paired with sucrose for participants who like sweet tastes, and conversely decreased liking and increased bitterness for quinine-paired odors. When odors were experienced in combination with sucrose when hungry, liking was not increased if tested sated, suggesting that expression of acquired liking for odors depends on current motivational state. Other studies report sensory-specific satiety is seen with food-related odors. Overall, these studies suggest that once an odor is experienced in a food-related context, that odor acquires the ability to modify both preparatory and satiety-related components of ingestion.     

Olfactory influences on appetite and satiety in humans

Odor stimuli play a major role in perception of food flavor. Food-related odors have also been shown to increase rated appetite, and induce salivation and release of gastric acid and insulin. However, our ability to identify an odor as food-related, and our liking for food-related odors, are both learned responses. In conditioning studies, repeated experience of odors with sweet and sour tastes result in enhanced ratings of sensory quality of the paired taste for the odor on its own. More recent studies also report increased pleasantness ratings for odors paired with sucrose for participants who like sweet tastes, and conversely decreased liking and increased bitterness for quinine-paired odors. When odors were experienced in combination with sucrose when hungry, liking was not increased if tested sated, suggesting that expression of acquired liking for odors depends on current motivational state. Other studies report sensory-specific satiety is seen with food-related odors. Overall, these studies suggest that once an odor is experienced in a food-related context, that odor acquires the ability to modify both preparatory and satiety-related components of ingestion.     

Odor mixture alters neural resources during symbolic problem solving

The smell of a cup of coffee is produced by many different odor chemicals combined in a mixture, yet the perception of that odor is of a single unified whole. Recent evidence has demonstrated that mixtures of odors share some of the same spatiotemporal features of speech sounds and may use similar brain resources in associating those features with the symbols they represent. This experiment investigated the hypothesis that an odor mixture would interfere with a math task that requires symbolic but not spatial processing. Results indicated the pattern of brain electrical activity was similar for the single odors and the mixture during spatial processing. During solution of the task requiring symbolic processing, the odor mixture produced a pattern of brain electrical activity different from the single odorants. These data suggest that the perception of odor mixtures may use some of the same resources associated with symbolic processing.     

Ambient odor of orange in a dental office reduces anxiety and improves mood in female patients

Essential oils have been used as remedies for a long time in different cultures across the world. However, scientific proof of such application is scarce. We included 72 patients between the ages of 22 and 57 while waiting for dental treatment in our study. The participants were assigned to either a control group (14 men, 23 women) or to an odor group (18 men and 17 women). Ambient odor of orange was diffused in the waiting room through an electrical dispenser in the odor group whereas in the control group no odor was in the air. We assessed by means of self-report demographic and cognitive variables, trait and state anxiety, and current pain, mood, alertness, and calmness. In this study, we report that exposure to ambient odor of orange has a relaxant effect. Specifically, compared to the controls, women who were exposed to orange odor had a lower level of state anxiety, a more positive mood, and a higher level of calmness. Our data support the previous notion of sedative properties of the natural essential oil of orange (Citrus sinensis).     

Remembering the past with slow breathing associated with activity in the parahippocampus and amygdala

Breathing plays an important role in perception of odors and the experience of emotions. We used the dipole tracing method to analyze brain areas related to odor-induced autobiographical memory and emotions estimated from averaged electroencephalograms triggered by inspiration onset during odor presentation. Odor stimuli were perfumes subjects named that elicited a specific, pleasant and personal memory as well as two pleasant odors for controls. The perfumes induced specific emotional responses during memory retrieval, arousal level of the memory, feelings of pleasantness and a sense of familiarity with the odor. Respiration measurement indicated that tidal volume increased and respiratory frequency decreased during presentation of perfume stimuli, showing a deep and slow breathing pattern. Throughout the olfactory stimulation, electroencephalograms and respiration were simultaneously recorded. In the averaged potentials, low frequency oscillation was phase-locked to inspiration. Dipole analysis showed that perfumes activated more widespread areas of the right parahippocampal cortex and converged in the right amygdala compared to control odors. Slow breathing synchronized with odor-induced autobiographical memory and emotions may be subconsciously stored in the parahippocampal cortex and amygdala.     

Odors released by stressed rats produce opioid analgesia in unstressed rats

When unstressed rats were placed in a chamber containing the odor of a conspecific that had received electric shock, they became analgesic as assessed by the formalin test. The odors of nonstressed conspecifics and novel odors produced no such effect. This analgesia was reversed by naltrexone. The data suggest that naturalistic stimuli innately associated with aversive environmental events can activate endogenous pain control mechanisms.     

Odor-induced changes in taste perception

We investigated odor-induced changes in taste perception (OICTP), by examining the influence of strawberry and soy sauce odors on perceived sweetness (Experiment 1) and saltiness (Experiment 2). We explored whether taste-smell interactions occur at the central level, by delivering odorants (strawberry, soy sauce, odorless water) and tastants (sucrose, sodium chloride) separately, and whether effects of imagined odors are comparable to those of physically presented odors. We found specific taste-smell interactions: sweetness enhancement induced by strawberry odor and saltiness enhancement induced by soy sauce odor. These interactions were elicited with separate delivery of olfactory and gustatory stimuli. Secondly, we found a similar but rather limited effect with the imagined odors: imagined strawberry enhanced perceived sweetness of water solutions, and imagined soy sauce enhanced perceived saltiness of weak sodium chloride solutions. We concluded that OICTP is a centrally mediated phenomenon, and that imagined odors can to some extent induce changes in perceived taste intensity comparable to those elicited by perceived odors.