Effect of environmental temperature on pleasure ratings of odors and tastes.

The pleasure ratings for alimentary and nonalimentary odors and tastes were tested in 10 subjects, at ambient temperatures 0°, 10°, 20°, 30° and 40°C. The taste stimuli were kept at 20°C and the odor stimuli at 36°C. The group median rating for all subjects and all nonalimentary substances did not change at any ambient temperatures. The increase in ambient temperature produced a moderate decrease in the median rating for alimentary stimuli. In another group of 8 subjects, alliesthesia was tested in a cold environment. Cold exposure almost completely suppressed negative alliesthesia to sweet stimuli. The return to 20°C restored alliesthesia. This phenomenon seems to be independent of the temperature of the solutions tasted. Nonalimentary odors were not affected by cooling.     

Alliesthesia to food cues: heterogeneity across stimuli and sensory modalities

Negative alliesthesia to olfactory and visual stimuli was assessed in 29 normal-weight women who, on alternate days, were either fasting or in a postprandial state after an ad libitum lunch. The participants were alternatively exposed to food and non-food pictures and odorants, and then rated for their hedonic appreciation (liking) and their desire to ingest (wanting) the evoked foods. While negative alliesthesia was observed only for food stimuli, it did not equally affect all food categories in either sensory modality. The stimuli representing foods eaten in typical local main dishes or having high energy density (e.g., pizza, bacon, beef, cheese) evoked clear negative alliesthesia, whereas this was not the case for those less consumed within a customary meal or associated with desserts (i.e., fruits). Furthermore, the visual food stimuli triggered a more negative shift in liking than did the food odours. Finally, the shift in wanting between pre- and post-meal state was more important than the shift in liking. These results suggest that alliesthesia may be influenced by both metabolic and non-metabolic factors.     

Emotional reactivity to odors: Olfactory sensitivity and the span of emotional evaluation separate the genders

Numerous studies report gender differences in emotional reactivity in health and disease and the perception of odors is closely linked to the limbic system. In order to investigate gender differences in the emotional perception of odors we extended the Sniffin’ Stick Test with analogue rating scales for hedonic (pleasantness/unpleasantness) and intensity estimates. We matched 172 healthy subjects (86 females and 86 males) on age in order to balance the study population for three age strata (A: 19–39 years, B: 40–59, C: 60 years and above). Overall odors in our statistical analysis demonstrated significant gender differences for the absolute hedonic estimates but not for the relative hedonic and not for the intensity estimates. These findings demonstrate that women evaluate the pleasantness of perceived odors in a more extreme manner than men without significant differences in hedonic polarity (pleasantness/unpleasantness). Thus, we report a singular significant effect of gender on the dimension valence (hedonic estimation) independent from the dimension intensity. Our findings are in accordance with gender differences in facial reactivity to auditory stimuli and differences in the evaluation of emotional pictures. Investigating olfactory sensitivity females detected n-butanol and discriminated the 16 odors of the test significantly better than males. These results indicate that females possess higher olfactory sensitivity.     

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.     

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.     

Origin of olfacto-gustatory alliesthesia: Intestinal sensitivity to carbohydrate concentration?

Gustatory and olfactory alliesthesia was observed in nine healthy adult humans who received on three different days an intragastric load of 50 g glucose dissolved into various amounts of water in order to make 100, 200 and 400 ml of solution. Maximal alliesthesia to sweet stimuli was observed with the smallest volume, i.e., highest concentration. Comparison of these results with previous results [7], obtained not by varying the volume but by varying the glucose mass, shows identity. Maximal alliesthesia to olfactory anchovy and Viandox^R was also observed after ingestion of the most concentrated gastric load. Maximal negative alliesthesia was observed about 45 min after the gastric load; thereafter alliesthesia tended to decrease. A gastric 200 ml load containing 40 g Mannitol, a nonabsorbed sugar, was followed by a strong negative alliesthesia to alimentary stimuli. Ten g glucose in 20 ml solution produced a more intense and rapid alliesthesia when injected into the duodenum than when injected into the stomach. It may be concluded that postinjective negative alliesthesia for alimentary stimuli can be caused by intraduodenal concentration of nutrients, probably sensed by duodenal nervous chemoreceptors.     

Taste and olfaction in human obesity

Earlier studies have shown differences between normal weight and obese humans in responsivity to external and internal stimuli. This study shows that normal weight and obese subjects do not differ in hedonic response to sucrose (taste) and benzaldehyde (odor). However, a perceptual typing of individuals based upon hedonic response is possible for both gustatory and olfactory processes. Ratings of pleasantness for the sweet taste of sucrose appear to generalize to the food-related odor of bitter almonds. The method of magnitude estimation as applied to the study of taste and olfaction in man may reveal relationship between changes in internal state and hedonic behavior.     

Olfactory lateralization: odor intensity but not the hedonic estimation is lateralized

An earlier study in humans comparing the olfactory sensitivity of both nostrils revealed a small but significant advantage of the right nostril for detection and for olfactory quality discrimination. However lateralization was not evaluated for the perception of odor intensity and hedonic evaluation (pleasantness/unpleasantness). Thus we investigated lateralization of olfactory intensity and hedonic evaluation in right-handed healthy volunteers (n=186) from the HeDoS-F database (Hedonic Database of Smell-Franconia). For olfactory evaluation the Sniffin' Stick Test was employed with the parameters detection, discrimination, identification and extended by analogue hedonic and intensity rating scales. Over all odors subjects rated the perceived intensity significantly higher following stimulation of the right compared to the left nostril. The analysis of the single odors of the Sniffin' Stick Test consistently confirmed higher intensity ratings for the right compared to the left nostril reaching a statistically significant difference for 10 out of 16 odors. In contrast we found no significant differences between the nostrils for the hedonic estimates over all odors. Differences in odor detection, discrimination and identification did not reach a statistically significant level, but for all these parameters the scores of the right nostril were slightly higher compared to the left nostril. For odor identification, however, a statistical tendency was observed. Based on our results we concluded that olfactory intensity estimates represent the most sensitive parameter of olfactory lateralization.     

Upper limb kinesthetic asymmetries: gender and handedness effects

Cross-modal interactions between vision, audition and touch have been extensively studied in the last decade. However, our understanding of how the chemical senses interact with other sensory modalities remains relatively scarce. We performed a cued auditory localization paradigm in healthy young adults by measuring reaction times to monaural auditory stimuli after subjects had been cued by unilateral olfactory stimuli, mixed olfactory/trigeminal stimuli or somatosensory stimuli. As expected, all cuing conditions led to enhanced performances in auditory localization. Further, both odors led to significantly shorter reaction times when compared to the somatosensory stimuli. We did not observe any effect of side-congruency between the cues and the targets. These results suggest facilitative effects of odorous cues independent of a possible trigeminal component in the interaction between olfaction and audition.     

Sensory stimulation and energy density in the development of satiety

To determine the contribution of sensory stimulation to the changing hedonic response to foods, the effects of consuming very low-calorie and higher calorie versions of soup and jello on the subjective pleasantness of foods were compared. Subjects were 24 normal weight females with low dietary restraint. Half the subjects were given test meals of low- and high-calorie tomato soup and half were given low- and high-calorie orange jello. They rated the pleasantness of the appearance, smell, texture and taste of nine sample foods as well as hunger and stomach fullness before and 2, 20, 40 and 60 min after consumption of the test meal. After the 60 min rating subjects were offered as much as they wanted to eat of a second course of cheese on crackers. Despite differences in the energy density of the test meals, there were no significant differences in the weights of food eaten in either the first or second course and no significant compensation in the second course for the energy differences of the first course. No differential effects of the caloric manipulation were observed in terms of hunger or fullness or in the development, time course and magnitude of sensory-specific satiety. That very low-calorie foods can produce sensory-specific satiety indicates that the sensory properties of foods are important for the changing hedonic response to foods as they are consumed.     

Negative alliesthesia for sweet stimuli after varying ingestions of glucose (author's transl)

Ten normal fasted subjects received sucrose gustatory stimului before and after intragastric glucose loads. Each subject in 4 experiments received 0 g, 25 g, 50 g and 100 g glucose. Responses to sweet stimuli were recorded during the period following injection. Results show a negative alliesthesia (decreased pleasure to sweet stimuli) appearing in 15 min increasing up to a maximum at about 55 min, then decreasing. The more glucose ingested the bigger the effect. These results are compatible with a participation of negative alliesthesia to the conscious satiey perception.     

Olfactory alliesthesia in human neonates: Prandial state and stimulus familiarity modulate facial and autonomic responses to milk odors

This study examines the effects of a shift in the motivational state (from hunger to satiety) of human neonates on their behavioral and autonomic responsiveness to artificial and food‐related odors as a function of stimulus familiarity. In Experiment 1, videotaped facial movements and autonomic (respiration rate: RR, heart rate: HR) responses to five olfactory stimuli (familiar regular formula, unfamiliar regular formula, protein hydrolysate formula, vanillin, control) are recorded in 3‐day‐old neonates (n = 14) during episodes of irregular sleep. The infants are tested on average 50 min. before and after bottle feeding. RR discriminates the odor stimuli from the control stimulus, indicating clear olfactory detection. Furthermore, neonates react with higher HR change only when exposed to their familiar formula milk during the postprandial condition. The measurement of facial movements with the Baby‐Facial Action Coding System indicates that disgust and aversive actions are more often evoked by the odor of regular formulas (familiar or unfamiliar) than by the other olfactory stimuli during the postprandial condition. In Experiment 2, untrained adult observers, presented with the videotapes of the infants' facial responses to the odors, are able to decode differential hedonic signals from the sender faces as a function of the infants' motivational states. The present findings are in line with the concept of olfactory alliesthesia as defined in adults. © 1999 John Wiley & Sons, Inc. Dev Psychobiol 35: 3–14, 1999     

Discovering Alzheimer's disease and bipolar disorder white matter effects building computer aided diagnostic systems on brain diffusion tensor imaging features

Responses to affective stimuli are usually studied in just one sensory system at a time. However, this is rarely the way they are experienced. We were interested in how combining affective stimuli of similar intensities across two sensory modalities (smell and vision) would affect both behavioral responses (ratings) and psychophysiological responses (skin conductance). We studied this using olfactory stimuli delivered birhinally while the subjects viewed affectively laden scenes on a computer screen. Bilateral skin conductance recordings were taken throughout. Subjects rated the pleasantness of the images that they were viewing. We found a particularly salient effect of unpleasant smells, which enhanced the pleasantness ratings of certain images and also the skin conductance responses to unpleasant images.     

The fish is bad: Negative food odors elicit faster and more accurate reactions than other odors

Dissociating between ‘good’ or ‘bad’ odors is arguable of crucial value for human survival, since unpleasant odors often signal danger. Therefore, negative odors demand a faster response in order to quickly avoid or move away from negative situations. We know from other sensory systems that this effect is most evident for stimuli from ecologically-relevant categories. In the olfactory system the classification of odors into the food or non-food category is of eminent importance. We therefore aimed to explore the link between odor processing speed and accuracy and odor edibility and valence by assessing response time and detection accuracy. We observed that reaction time and detection accuracy are influenced by both pleasantness and edibility. Specifically, we showed that an unpleasant food odor is detected faster and more accurately than odors of other categories. These results suggest that the olfactory system reacts faster and more accurately to ecologically-relevant stimuli that signal a potential danger.     

Facial consummatory responses in rats support the ponderostat hypothesis

Facial consummatory responses reflecting ingestive and aversive perceptions were studied and quantified in rats chronically implanted with gastric and oral catheters. A gustatory stimulus of 50 microliters of 1.75 mol.1-1 sucrose was injected into the mouth every 5 min during 60 min. At time zero, 1.7 ml of 3.3 mol.1-1 glucose was injected into the stomach. Typical ingestive facial consummatory responses were observed in response to sweet stimuli prior to the gastric load. Aversive consummatory responses were observed in response to sweet stimuli after the glucose gastric load (negative alliesthesia). The rats were then fasted until they had lost about 14% of their body weight (from 411 +/- 34 g to 353 +/- 28 g). When lean, the rats were subjected to the same gustatory session as in the control period described above. In lean rats the gastric load of glucose was not followed by negative alliesthesia in response to sweet oral stimuli. In the last part of the experiment the rats were fed ad lib and they recovered their initial body weight. When the rats were subjected again to the same gustatory sessions, the gastric load was followed by negative alliesthesia in response to sweet stimuli. Thus, after recovering their initial body weight, the rats displayed the same response as in the control sessions prior to losing weight. These results in rats parallel results obtained in human subjects, and reinforce the hypothesis of the existence of a ponderostat regulating body mass.     

Injection of glucose into the superior mesenteric artery in man, absence of negative alliesthesia in response to sweet stimuli (author's transl)

Two groups of ten human subjects received 30 g or 50 g respectively of glucose injected into the arteria mesenterica superior. Sweet gustatory sensation was explored by presenting a range of solutions. The evolution of hedonic responses before and after intraarterial glucose loads was recorded by asking the subjects to score pleasantness and unpleasantness on a +2, ?2 scale. Intraarterial glucose load did not affect the responses. It is concluded that the negative alliesthesia normally occurring after oral and intragastric feeding does not have its origin in hepatic glucoreceptors.     

Impairment of odor recognition in Parkinson's disease caused by weak activations of the orbitofrontal cortex

Olfactory dysfunction and abnormalities of olfactory brain structures are found in patients with Parkinson's disease (PD), and a number of studies have reported that olfactory dysfunction is caused by abnormalities of the central olfactory systems. We previously analyzed electroencephalograms (EEGs) and respiration simultaneously in normal subjects while testing for detection and recognition of odors. We identified changes in respiration pattern in response to odor stimuli and found inspiratory phase-locked alpha oscillations (I-alpha). The genesis of I-alpha were identified in olfactory-related areas including the entorhinal cortex, hippocampus, amygdale and orbitofrontal cortex with an EEG dipole tracing method. In the present study, we used the same protocol in PD patients and compared results of PD with those of age-matched controls. All PD patients detected odor, but 5 out of 10 showed impaired odor recognition. Changes in breathing pattern associated with emotional changes during exposure to odor stimuli were not observed in PD patients. I-alpha waveforms were not observed; however, positive waves followed by negative waves were identified approximately 100ms after inspiration onset. Dipoles of this component were localized in the entorhinal cortex for odor detection in all patients and in the entorhinal cortex and middle temporal gyrus for PD patients who could discriminate odors. Odor recognition in PD could be subserved by a different neural circuit from that of normal subjects, done through the temporal association cortex as a subsystem for recognizing the odor; however, the system may not be associated with the odor-induced emotions.     

Sensory and metabolic feedback in the modulation of taste hedonics

One hundred and twenty-five college students were fed a small preload composed of common foods which were either solid or liquid, sweet or non-sweet, and high or low in energy content. At 15-minute intervals following the preload subjects rated the intensity and pleasantness of either a sweet or a non-sweet test stimulus. Pleasantness reductions (alliesthesia) were observed following all preloads but were significantly larger in the high-calorie groups. In addition, solid preloads were found to provoke greater hedonic shifts than liquid preloads. While intensity ratings paralleled those for pleasantness, no correlation between the two was apparent. The results point to a metabolic explanation for the hedonic declines in the test stimuli. Nutrient (perhaps carbohydrate) detectors in the upper GI tract are proposed to trigger both central and peripheral changes which underlie the changes in pleasantness and intensity judgements.     

Androgen effects on responsiveness to aggression and stress-related odors of male mice

The effect of male gonadal hormones on responsiveness to the aggression and stress-related odors of male mice was examined. The initial experiment indicated that intact male mice would avoid an area of an open field that had been spotted with the urine of aggressive male donors, while castration of the subjects eliminated the response. Hormone replacement was effective in reinstating the aversion, clearly demonstrating the androgen-dependent nature of the response. A second experiment determined that the effects of castration do not generalize to another type of aversive odor, namely the alarm odors of castrate donors. That is, both intact and castrate males exhibited a pronounced aversion to the urine odors of castrates that had been subjected to a prolonged period of stress. These results suggest that gonadal hormone effects on olfactory responsivity are somewhat specific, and more interestingly, that the mechanism behind the effects of gonadal hormones on rodent aggression may lie in their influence on the nature of the response to the relevant olfactory stimuli.