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.     

Emotional qualities of odors and their influence on the startle reflex in humans

Recent human and animal research suggests that the startle reflex might serve as a psychophysiological indicator of the emotional valence of foreground stimulation. The present experiment was designed to evaluate the emotional effects of positive and negative odorant stimuli. We examined the effects of continuous hydrogen sulphide (H2S) and vanillin stimulation on the magnitude of the acoustic startle reflex (measured at the M. orbicularis oculi) and on ratings of subjective valence in 16 healthy subjects. In accordance with the view that odors have emotional qualities, we found that H2S, a presumed negative foreground stimulus, significantly enhanced the startle-reflex amplitude relative to neutral air stimulation, whereas vanillin, a positive foreground stimulus, tended to reduce the reflex amplitude compared with neutral air stimulation. Both odorant stimuli were rated as equally intense by the subjects, and heart rate and electrodermal activity were not affected differentially by the two odorants.     

Topographical differences in the sensitivity of the human nasal mucosa to olfactory and trigeminal stimuli

The olfactory and trigeminal systems play a role in the sensation of odors. The intrinsic optical signal (IOS) imaging method allows visualization of the neuronal activity. The IOS was measured after the nasal epithelium had been exposed to olfactory (H(2)S) and trigeminal (CO(2)) stimuli. The IOS was measured in the area of the middle turbinate. The response patterns of H(2)S and CO(2) on the middle turbinate were different, and some overlap between regions of activation was also observed. The response to CO(2) (20%) on the medial side of the middle turbinate was significantly higher than the response on the lateral side. In contrast, the response to H(2)S (5.6 ppm) was greater on the lateral side than on the medial side. There were no significant differences in response between the medial and lateral sides of the middle turbinate to stimuli of lower concentration (H(2)S 2.8 ppm, CO(2) 5% and 10%). These data suggest that the middle turbinate has regions which are sensitive to both olfactory and trigeminal stimuli.     

Emotional reactivity of the airways in asthma: Consistency across emotion-induction techniques and emotional qualities

Considerable individual differences exist in asthma patients’ airway responses to emotional stimuli, but little is known about the generalization of such responses across situations or states of airways constriction. Fifty-four asthma patients and 25 healthy controls viewed in two separate sessions, films and blocks of pictures from each of three emotional qualities, pleasant, unpleasant, and neutral. At the beginning of each session, patients received a placebo or anti-cholinergic bronchodilator (ipratropium bromide), respectively, in a randomized double-blind design. Respiratory resistance, reactance and impedance were recorded throughout stimulus presentations with impulse oscillometry. Resistance increases showed a moderate degree of generalization across unpleasant films and pictures, unpleasant and pleasant pictures, as well as cholinergic blockade and placebo. Thus, the intensity of airway responses to unpleasant emotional stimuli is a moderately stable characteristic of asthma patients. In addition to the central airway, peripheral and extrathoracic airways may also contribute the consistency of such responses.     

Olfactory bulbectomy and gender differences in maternal behaviors of rats

Olfactory bulbectomy markedly reduced the number of days required before maternally inexperienced female and male animals retrieved pups. Bulbectomy eliminated a difference between the genders in the latency to retrieve, but did not affect differences with regard to other aspects of maternal behavior. The results were similar to those obtained with peripherally-induced anosmia and suggest that differences in functioning of the olfactory system may play a role in gender dimorphic behaviors.     

Blood pressure changes highlight gender differences in emotional reactivity to arousing pictures

The current study was aimed at investigating the effects of gender on the magnitude and patterning of blood pressure responses to specific pleasant and unpleasant, arousing visual stimuli. Systolic and diastolic blood pressure (SBP and DBP), as well as heart rate (HR) and skin conductance (SCR) responses were investigated during picture viewing in 21 female and 25 male students. The pattern of SCR and HR reactivity across emotional categories was found to be similar for men and women. Gender was found to be an effective moderator of BP responses specifically to sexual stimulus content, which prompted greater reactivity in men than in women. These findings extend prior research on gender differences in autonomic responding to emotional visual stimuli and suggest that BP changes might reflect sexual peripheral arousal more than other autonomic measures.     

Olfactory dysfunction in the pathophysiological continuum of dementia

Sensory capacities like smell, taste, hearing, vision decline with aging, but increasing evidence show that sensory dysfunctions are one of the early signs diagnosing the conversion from physiological to pathological brain state. Smell loss represents the best characterized sense in clinical practice and is considered as one of the first preclinical signs of Alzheimer’s and Parkinson’s disease, occurring a decade or more before the onset of cognitive and motor symptoms. Despite the numerous scientific reports and the adoption in clinical practice, the etiology of sensory damage as prodromal of dementia remains largely unexplored and more studies are needed to resolve the mechanisms underlying sensory network dysfunction. Although both cognitive and sensory domains are progressively affected, loss of sensory experience in early stages plays a major role in reducing the autonomy of demented people in their daily tasks or even possibly contributing to their cognitive decline. Interestingly, the chemosensory circuitry is devoid of a blood brain barrier, representing a vulnerable port of entry for neurotoxic species that can spread to the brain. Furthermore, the exposure of the olfactory system to the external environment make it more susceptible to mechanical injury and trauma, which can cause degenerative neuroinflammation. In this review, we will summarize several findings about chemosensory impairment signing the conversion from healthy to pathological brain aging and we will try to connect those observations to the promising research linking environmental influences to sporadic dementia. The scientific body of knowledge will support the use of chemosensory diagnostics in the presymptomatic stages of AD and other biomarkers with the scope of finding treatment strategies before the onset of the disease.     

Watching emotional movies: Affective reactions and gender differences

Previous studies have found that unpleasant film clips depicting mutilated bodies or injuries evoke a sustained heart rate deceleration which has been interpreted as reflecting a stimulus-specific aversive response or as increased orienting and attentional processing that varies with stimulus significance. Few studies, however, have examined cardiac changes during the viewing of high arousal pleasant films. To clarify this issue, the present study assessed evaluative, facial and autonomic reactions in both men and women during the viewing of highly arousing pleasant, as well as unpleasant, films. Results indicated a similar skin conductance increase and heart rate deceleration which were greater than those observed during the viewing of a neutral film. Compared to men, women rated both films as less pleasant and rated the unpleasant film as more arousing. The present findings suggest that sustained exposure to pleasant and unpleasant stimuli elicit similar cardiac orienting when stimuli are equated for subjective report of emotional arousal.     

Learned aversion to the odors of male mice: Effects on agonistic behavior

Intact and castrate male mice were subjected to avoidance training using the urine of intact and castrate donors as stimuli. Both intacts and castrates learned to discriminate between the odors, with such learning modifying their spontaneous responsiveness to such odors in an open field in the predicted direction. This result suggests that the previously reported lack of responsiveness in castrates [15] was not due to a simple sensory deficit. A second experiment determined that increasing the relative aversion exhibited by intact subjects to the odors of intact donors also increased the subject's aggression directed at a castrate opponent swabbed with such odors. Modification of castrates' responsivity had no such effect on their aggression. This indicated that replacing the responsivity to aggression-related odors which is lost following castration, is not equivalent to replacing the hormone. The results are discussed with regard to possible hormonal effects on the social significance of olfactory cues to the recipient animal.     

Shifting the focus of attention modulates amygdala and anterior cingulate cortex reactivity to emotional faces

Functional neuroimaging studies have largely established the prominence of amygdala during emotion processing and prefrontal areas such as anterior cingulate cortex (ACC) during attentional modulation. In general, emotion processing paradigms known to probe amygdala have not been adapted to recruit prefrontal areas. In this study we used a well-known perceptual face matching paradigm, designed to elicit amygdala response, and asked volunteers to shift their focus in order to recruit regions responsible for attentional control. Stimuli comprised a trio of geometric shapes (circles, rectangles, triangles) presented alongside a trio of emotional faces (angry, fear, or happy) within the same field of view, and subjects were instructed to Match Faces or Match Shapes, as a means of attending to and away from the emotional content, respectively. We observed greater amygdala reactivity to Match Faces (>Match Shapes), and greater rostral ACC response to Match Shapes (>Match Faces). Results indicate that simply and volitionally directing attention toward or away from emotional content correspondingly modulates amygdala and ACC activity.     

Preference for natural odors in rat pups: Implications of a failure to replicate

The results of the present experiment indicate that very minor changes in the diet on which a rat dam is maintained can have profound effects on the attractiveness of her feces to her pups. Rat pups exhibited a strong preference for the odor of feces taken from dams maintained on one sample of Purina Rodent Laboratory Chow No. 5001, but no preference for the odor of the feces of dams maintained on a second sample of the same diet. These data point to the need for very great care in the design of experiments employing, as independent variables, stimuli which are not under direct experimenter control. The results also suggest that experience of a natural odor during ontogeny may not be sufficient for the development of a preference for that odor in young rats.     

Sex differences in the neural correlates of emotion: evidence from neuroimaging

Sex differences in emotional processes represent some of the most robust sex stereotypes worldwide. However, empirical support for these stereotypes is lacking, especially from research utilizing objective measures, such as neuroimaging methodologies. We conducted a selective review of functional neuroimaging studies that have empirically tested for sex differences in the association between brain function and emotional processes (including perception, reactivity, regulation and experience). Evidence was found for marked sex differences in the neural mechanisms underlying emotional processes, and in most cases suggested that males and females use different strategies during emotional processing, which may lead to sex differences in the observed (or subjectively reported) emotional process. We discuss how these findings may offer insight into the mechanisms underlying sex differences in emotional behaviors, and outline a number of methodological considerations for future research. Importantly, results suggest that sex differences should not be ignored in research investigating the neurobiology of emotion.     

Effects of maternal state on the responsiveness to nest odors of hooded rats

Systemic antagonism of H1 or H2 receptors for histamine attenuated drinking elicited by SC 20 mg/kg histamine in adult male Sprague-Dawley rats. The H1 antagonist dexbrompheniramine (DXB; 0.5-16 mg/kg) and the H2 antagonist cimetidine (C; 0.5-100 mg/kg) each inhibited drinking elicited by histamine when given IP 10 min prior to SC histamine: The lowest doses to produce a statistically significant inhibition of drinking were 2 mg/kg DXB and 32 mg/kg C. While 1 mg/kg DXB alone or 16 mg/kg DXB plus 16 mg/kg C virtually abolished drinking elicited by histamine (1.25-20 mg/kg) in a dose-response study. In addition, such combined antagonism of H1 and H2 receptors failed to elicit drinking in the absence of exogenous histamine and failed to inhibit drinking elicited by deprivation from water for 7 or 24 hr. Because combined systemic antagonism of H1 and H2 receptors can specifically and completely inhibit drinking elicited by exogenous histamine, these findings provide a probe for a histaminergic component of drinking in the rat.     

Frontal brain asymmetry and emotional reactivity: A biological substrate of affective style

Individuals differ dramatically in the quality and intensity of their response to affectively evocative stimuli. On the basis of prior theory and research, we hypothesized that these individual differences are related to variation in activation of the left and right frontal brain regions. We recorded baseline brain electrical activity from subjects on two occasions 3 weeks apart. Immediately following the second recording, subjects were exposed to brief positive and negative emotional film clips. For subjects whose frontal asymmetry was stable across the 3-week period, greater left frontal activation was associated with reports of more intense positive affect in response to the positive films, whereas greater right frontal activation was associated with more intense reports of negative affect in response to the negative film clips. The methodological and theoretical implications of these data are discussed.     

Emotional reactivity,emotional eating,and obesity: A naturalistic study

Laboratory studies indicate that obese individuals are more emotionally reactive and more likely to overeat when distressed than are those of normal weight. These studies were conducted under highly artificial conditions, however, and their generality outside of the laboratory remains largely untested. The present study compared the emotional reactivity and emotional eating of normal and overweight female college students in the natural environment. Subjects self-monitored their food intake and mood just prior to each instance of eating for 12 consecutive days. The results indicated that obese subjects were more emotionally reactive and more likely to engage in emotional eating than normals, but these findings applied only to snacks, not to meals. Correlational analyses indicated that emotional distress associated with snacks and emotional eating associated with both snacks and meals were related to subjects' percentage overweight. The two groups did not differ on any measure of positive emotions of consumption following positive emotions, nor were these two variables related to percentage overweight. The theoretical and clinical implications of these findings are briefly discussed.     

Pre‐ to postsleep change in psychophysiological reactivity to emotional films: Late‐night REM sleep is associated with attenuated emotional processing

Rapid eye movement (REM) sleep has been postulated to facilitate emotional processing of negative stimuli. However, empirical evidence is mixed and primarily based on self‐report data and picture‐viewing studies. This study used a full‐length aversive film to elicit intense emotion on one evening, and an emotionally neutral control film on another evening while psychophysiological and experiential responses were measured. Subsequent sleep was monitored polysomnographically, and specific film scenes were presented again on the next morning. Correlation analyses revealed that participants with longer late‐night REM sleep after the aversive film showed higher increase of electrodermal reactivity and less reduction of facial corrugator muscle reactivity to negative film scenes on the next morning. This indicates that REM sleep may be associated with attenuated emotional processing of prolonged and intense emotional stimuli from pre‐ to postsleep.     

Goal relevance and goal conduciveness appraisals lead to differential autonomic reactivity in emotional responding to performance feedback

Using an appraisal framework, the present experiment tested the hypothesis that goal relevance and goal conduciveness have an interactive effect on emotional responding. We expected that elicitation of positive or negative emotions in response to events that are conducive or obstructive to attainment of one's goals depends on the level of goal relevance. To test this hypothesis, we presented 119 participants with positive (success) or negative (failure) performance feedback of high or low relevance in an achievement context. Feeling self-report showed effects of conduciveness, but no interaction with relevance. Physiological reactivity showed the predicted interaction effect on cardiac autonomic regulation (CAR), with higher CAR for high-relevance conducive than obstructive conditions. Moreover, mean arterial pressure (MAP) and skin conductance level (SCL) differed between conducive and obstructive conditions, and heart rate (HR) and SCL differed between relevance conditions. Implications for the plausibility and current empirical support of the interaction hypothesis are discussed.     

Environmental Effects Exceed Genetic Effects on Perceived Intensity and Pleasantness of Several Odors: A Three-Population Twin Study

Human genes encoding odorant receptors have been identified, but the contribution of genetic effects to total variation in specific odor perceptions is largely unknown. We estimated the relative contributions of genetic and environmental effects to variation in the perceived intensity and pleasantness of cinnamon, chocolate, turpentine, and isovaleric acid (sweaty) odors by quantitative genetic modeling of odor rating data from 856 twin individuals (including 83 complete monozygotic and 275 dizygotic twin pairs) aged 10–60 years (44% males and 56% females) from Australia, Denmark, and Finland. Results from fitting univariate models including components for additive genetic (A), shared environmental (C), and non-shared environmental (E) effects to the data implied that non-shared environmental effects account for the most variation in ratings of individual odors while genetic effects play only a minor role. Multivariate independent pathway model revealed a modest but significant common additive genetic component for intensity ratings, explaining 18% of the total variation. The results promote the importance of inter-individual variation in odor exposures and olfactory plasticity to odor perception. Edited by Deborah Finkel.     

Emotional reactivity to emotional and smoking cues during smoking abstinence: Potentiated startle and P300 suppression

Negative affect is thought to be an important factor in the maintenance of cigarette smoking, and thus it is important to further develop objective measures of smoking‐related emotional responses. Nonsmokers, nonabstinent smokers, and abstinent smokers participated in a cue reactivity task where eyeblink startle amplitude and startle probe P300 (P3) suppression were measured during the presentation of emotional pictures. During unpleasant pictures, the amplitude of both measures was smaller in nonabstinent smokers than in nonsmokers or abstinent smokers. P3 suppression, but not startle amplitude, was larger in abstinent smokers than in nonsmokers. Abstinence‐induced increases in cigarette craving were associated with P3 suppression during tobacco‐related pictures. Results suggest that tobacco abstinence increases emotional reactivity to unpleasant stimuli, which is consistent with negative reinforcement models of tobacco addiction.     

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.