Pleasant or Unpleasant: Attentional Modulation of Odor Perception

Using positron emission tomography, we investigated whether regional brain activations differ as a function of attending to pleasant versus unpleasant components of odors. There were two experimental (attention to pleasantness and attention to unpleasantness) and one control (baseline) condition. The stimuli presented during the two experimental conditions were exactly the same (three binary mixtures, each consisting of one pleasant and one unpleasant compound), but the affective property to which participants?? attention was directed was different: They indicated with a mouse click whether each stimulus contained a pleasant (during attention to pleasantness) or unpleasant (during attention to unpleasantness) odor. During baseline, odorless stimuli were presented, and participants pressed the mouse button randomly after each one. Several brain regions were involved in both types of attention, and these included ventral striatum, right orbitofrontal cortex, and anterior cingulate cortex. Subtle differences were also revealed: Attending to pleasantness was associated preferentially with a sensory/perceptual network (piriform cortex and amygdala), whereas attending to unpleasantness engaged a component of the attentional (right parietal) network. Thus, we delineate neural substrates of attending to olfactory pleasantness and unpleasantness, some of which are common to both and others that are specific to pleasantness or to unpleasantness. Our results suggest that the view of the mesolimbic dopaminergic system as the reward network that responds selectively to positive reinforcers is somewhat limited: Our findings are more in keeping with a view of this set of structures as the salience system of the brain.     

Rat trigeminal, olfactory and taste responses after capsaicin desensitization

Experiment 1 showed that capsaicin injections severely reduced or eliminated nasal trigeminal responses to 3 odorants. Experiments 2 and 3 investigated whether desensitized animals could behaviorally detect and discriminate odors. Capsaicin treated animals had no measurable deficits in locating buried food, in odor aversion learning, or in operant odor detection and discrimination. Experiment 4 examined whether behavioral responsiveness to salty, sour and bitter tastes was affected by desensitization. Capsaicin injections did not affect responsiveness to salty or sour, but may have raised rejection thresholds for bitter. Broadly, the present results suggest that substance P-containing fibers mediate trigeminal responsiveness to odorants and irritants but that the loss of this responsiveness does not appreciably affect smell or taste, per se.     

Brain activation during odor perception in males and females.

Several studies indicate that women outperform men in olfactory identification tasks. The psychophysical data are more divergent when it comes to gender differences at levels of odor processing which are cognitively less demanding. We therefore compared cerebral activation with H2(15)O PET in 12 females and 11 males during birhinal passive smelling of odors and odorless air. The odorous compounds (odorants) were pure olfactory, or mixed olfactory and weakly trigeminal. Using odorless air as the baseline condition, activations were found bilaterally in the amygdala, piriform and insular cortices in both sexes, irrespective of the odor. No gender difference was detected in the pattern of cerebral activation (random effect analysis SPM99, corrected p < 0.05) or in the subjective perception of odors. Males and females seem to use similar cerebral circuits during the passive perception of odors. The reported female superiority in assessing olfactory information including odor identification is probably an effect of a difference at a cognitive, rather than perceptive level of olfactory processing.     

Context effects on saccade-related brain potentials to words during reading

In two experiments saccade-related brain potentials (SRPs) to sentences were investigated under conditions approximating natural reading. Our aim was to look for electrophysiological (SRP) signs of sentence context on the processing of final words that were either congruent or incongruent with the meaning of the sentence. In Experiment 1 subjects indicated by a button-press whether or not the final word was congruent with the context, while in Experiment 2 they read silently without an overt decision. In Experiment 1, SRPs to incongruent words were more negative than SRPs to congruent words between 80-310 msec (from saccade offset). In Experiment 2, however, the inconcruent SRPs became more negative than the congruent SRPs only between 280-460 msec. These results suggest that in Experiment 1, during the processing of incongruent words the early sign of registering mismatch appears simultaneously with the analysis of the visual features of the word.     

A bittersweet symphony: Evidence for taste-sound correspondences without effects on taste quality-specific perception

Music has been associated with taste and shown to influence the dining experience. We asked whether sound that is associated with taste affects taste perception of food. In two studies (study 1: N = 20, 13 women; study 2: N = 20, 17 women), participants evaluated the taste of cinder toffee while listening to either of two soundscapes associated with sweet and bitter taste, respectively, or no sound. In study 1, participants rated the taste on a visual-analog scale (VAS) anchored with “bitter” and “sweet”, aiming to replicate a previous study (Crisinel et al., 2012 ). In contrast, four separate scales were used in study 2 to report the extent of bitter, sweet, sour, and salty taste to test whether taste qualities were influenced by sound differentially. Additionally, taste intensity and pleasantness were rated in both studies. Taste intensity was increased in the presence of a sound, while pleasantness was not affected. In study 1, sound shifted bitter-sweet ratings in the direction of the congruent sound, i.e. samples tasted sweeter with “sweet” sound and more bitter with “bitter” sound, replicating Crisinel et al.'s ( 2012 ) results. However, this effect was abolished when a “no-sound” control was included in the statistical model. Taste ratings in study 2 showed no effect of sound on any specific taste quality, suggesting that the influence of sound on taste in study 1 reflects an artifact of the scale rather than an actual shift in perception. Together, the data provide evidence for taste-sound correspondences without effects on taste-quality specific perception.     

Relationship between odor perception and depression in the Japanese elderly

Abstract Odor perception has been studied in patients with various mental disorders; however, no consensus has been reached as to its detection, identification, or pleasantness/unpleasantness of odors especially in patients with depression. One hundred and nineteen normal elderly individuals living at home were exposed to odors of rose, perfume, white ginger, Indian ink, cigarette smoke, milk, feces and orange scent using the scratch and sniff method. They were asked to rate the strength of each odor, its pleasantness or unpleasantness, their liking for it, and their familiarity with it. They were also asked to complete a self-rating depression scale (SDS). The relationship of the score of each psychological olfactory scale with the SDS score and the difference in the score of each psychological scale between high-SDS and low-SDS groups are discussed.     

Electrophysiological correlates of visual affective priming

The present study used event-related potentials (ERPs) to investigate the underlying neural mechanisms of visual affective priming. Eighteen young native English-speakers (6 males, 12 females) participated in the study. Two sets of 720 prime-target pairs (240 affectively congruent, 240 affectively incongruent, and 240 neutral) used either words or pictures as primes and only words as targets. ERPs were recorded from 64 scalp electrodes while participants pressed either "Happy" or "Sad" buttons to indicate target pleasantness. The response time (RT) results confirmed an affective priming effect, with faster responses to affectively congruent trials (659 ms) than affectively incongruent trials (690 ms). Affectively incongruent trials had larger and more negative N200 activation than those to neutral trials. Importantly, a delayed N400 for word prime-target pairs matched the RT results with larger negative amplitudes for incongruent than congruent pairs. This finding suggests that the N400 component is not only sensitive to semantic mismatches, but is also sensitive to affective mismatches for word prime-target pairs.     

On-line psychophysical data acquisition and event-related fMRI protocol optimized for the investigation of brain activation in response to gustatory stimuli

An experimental method for event-related functional magnetic resonance imaging that allows for the presentation of several chemosensory stimuli in the oral cavity during the same run, the collection of psychophysical measures (intensity or pleasantness) during the presentation of the stimuli, and the analysis of the data in an event-related fashion are described. The automatic pumps used to present taste stimuli allowed for multiple tastes to be delivered in small amounts under computer control. Psychophysical ratings of pleasantness or intensity were collected after each presentation of a taste stimulus and water, with the general labeled magnitude scale, using a joystick that controlled the movement of an arrow on the visual display. Performing these cognitive tasks required that the participant remained focused, and aided in the interpretation of the data collected. The perceived pleasantness differed across stimuli for all conditions; however, pleasantness ratings for the same stimulus displayed consistency, over the duration of the run and before each scan on separate days. Activation in response to sucrose and caffeine while the participant rated pleasantness was found in the insula, frontal operculum, rolandic operculum and orbitofrontal cortex which is consistent with previous taste fMRI studies.     

Neural correlates of evaluative compared with passive tasting

We used functional magnetic resonance imaging to test the hypothesis that the nature of the neural response to taste varies as a function of the task the subject is asked to perform. Subjects received sweet, sour, salty and tasteless solutions passively and while evaluating stimulus presence, pleasantness and identity. Within the insula and overlying operculum the location of maximal response to taste vs. tasteless varied as a function of task; however, the primary taste cortex (anterior dorsal insula/frontal operculum – AIFO), as well as a more ventral region of anterior insula, responded to taste vs. tasteless irrespective of task. Although the response here did not depend upon task, preferential connectivity between AIFO and the amygdala (bilaterally) was observed when subjects tasted passively compared with when they performed a task. This suggests that information transfer between AIFO and the amygdala is maximal during implicit processing of taste. In contrast, a region of the left lateral orbitofrontal cortex (OFC) responded preferentially to taste and to tasteless when subjects evaluated pleasantness, and was preferentially connected to earlier gustatory relays (caudomedial OFC and AIFO) when a taste was present. This suggests that processing in the lateral OFC organizes the retrieval of gustatory information from earlier relays in the service of computing perceived pleasantness. These findings show that neural encoding of taste varies as a function of task beyond that of the initial cortical representation.     

Psychophysical assessment of the affective components of non-painful touch.

A novel psychophysical procedure for the evaluation of the affective components of touch was developed. A fabric material was stroked across the test site at a controlled direction and velocity, after which the subject provided a numerical estimate of pleasantness. Significant differences were detected for the sites tested (FACE vs ARM), the fabric materials used (VELVET, COTTON and PLASTIC MESH), and the velocity of motion (0.5, 5 and 50 cm/s). Attesting to their validity, estimates of pleasantness correlated negatively with estimates of unpleasantness obtained for the same stimuli. Moreover, subjects were reasonably consistent in their ratings upon stimulus replication. These findings demonstrate that the hedonic qualities of touch can be psychophysically evaluated, and that valid and reliable estimates are obtained.     

Repetitive transcranial magnetic stimulation of Broca's area affects verbal responses to gesture observation

The aim of the present study was to determine whether Broca's area is involved in translating some aspects of arm gesture representations into mouth articulation gestures. In Experiment 1, we applied low-frequency repetitive transcranial magnetic stimulation over Broca's area and over the symmetrical loci of the right hemisphere of participants responding verbally to communicative spoken words, to gestures, or to the simultaneous presentation of the two signals. We performed also sham stimulation over the left stimulation loci. In Experiment 2, we performed the same stimulations as in Experiment 1 to participants responding with words congruent and incongruent with gestures. After sham stimulation voicing parameters were enhanced when responding to communicative spoken words or to gestures as compared to a control condition of word reading. This effect increased when participants responded to the simultaneous presentation of both communicative signals. In contrast, voicing was interfered when the verbal responses were incongruent with gestures. The left stimulation neither induced enhancement on voicing parameters of words congruent with gestures nor interference on words incongruent with gestures. We interpreted the enhancement of the verbal response to gesturing in terms of intention to interact directly. Consequently, we proposed that Broca's area is involved in the process of translating into speech aspects concerning the social intention coded by the gesture. Moreover, we discussed the results in terms of evolution to support the theory [Corballis, M. C. (2002). From hand to mouth: The origins of language. Princeton, NJ: Princeton University Press] proposing spoken language as evolved from an ancient communication system using arm gestures.     

Effect of Magnitude Estimation of Pleasantness and Intensity on fMRI Activation to Taste

The goal of the present study was to investigate whether the psychophysical evaluation of taste stimuli using magnitude estimation influences the pattern of cortical activation observed with neuroimaging. That is, whether different brain areas are involved in the magnitude estimation of pleasantness relative to the magnitude estimation of intensity. fMRI was utilized to examine the patterns of cortical activation involved in magnitude estimation of pleasantness and intensity during hunger in response to taste stimuli. During scanning, subjects were administered taste stimuli orally and were asked to evaluate the perceived pleasantness or intensity using the general Labeled Magnitude Scale (Green et al., Chem Senses, 21(3), 323-334, 1996; Bartoshuk et al., Physiol Behav, 82(1), 109-114, 2004). Image analysis was conducted using Analysis of Functional NeuroImage software. Magnitude estimation of intensity and pleasantness shared common activations in the insula, rolandic operculum, and the medio-dorsal nucleus of the thalamus. Globally, magnitude estimation of pleasantness produced significantly more activation than magnitude estimation of intensity. Areas differentially activated during magnitude estimation of pleasantness versus intensity included, e.g., the insula, the anterior cingulate gyrus, and putamen, suggesting that different brain areas were recruited when subjects made magnitude estimates of intensity and pleasantness. These findings demonstrate significant differences in brain activation during magnitude estimation of intensity and pleasantness to taste stimuli. An appreciation for the complexity of brain response to taste stimuli may facilitate a clearer understanding of the neural mechanisms underlying eating behavior and overconsumption.     

Common and specific neural correlates underlying the spatial congruency effect induced by the egocentric and allocentric reference frame

The spatial location of an object can be represented in two frames of reference: egocentric (relative to the observer's body or body parts) and allocentric (relative to another object independent of the observer). The object positions relative to the two frames can be either congruent (e.g., both left or both right) or incongruent (e.g., one left and one right). Most of the previous studies, however, did not discriminate between the two types of spatial conflicts. To investigate the common and specific neural mechanisms underlying the spatial congruency effect induced by the two reference frames, we adopted a 3 (type of task: allocentric, egocentric, and color) × 2 (spatial congruency: congruent vs. incongruent) within‐subject design in this fMRI study. The spatial congruency effect in the allocentric task was induced by the task‐irrelevant egocentric representations, and vice versa in the egocentric task. The nonspatial color task was introduced to control for the differences in bottom‐up stimuli between the congruent and incongruent conditions. Behaviorally, significant spatial congruency effect was revealed in both the egocentric and allocentric task. Neurally, the dorsal‐medial visuoparietal stream was commonly involved in the spatial congruency effect induced by the task‐irrelevant egocentric and allocentric representations. The right superior parietal cortex and the right precentral gyrus were specifically involved in the spatial congruency effect induced by the irrelevant egocentric and allocentric representations, respectively. Taken together, these results suggested that different subregions in the parieto‐frontal network played different functional roles in the spatial interaction between the egocentric and allocentric reference frame. Hum Brain Mapp 38:2112–2127, 2017. © 2017 Wiley Periodicals, Inc.     

Activation in the angular gyrus and in the pSTS is modulated by face primes during voice recognition

The aim of the present study was to better understand the interaction of face and voice processing when identifying people. In a S1‐S2 crossmodal priming fMRI experiment, the target (S2) was a disyllabic voice stimulus, whereas the modality of the prime (S1) was manipulated blockwise and consisted of the silent video of a speaking face in the crossmodal condition or of a voice stimulus in the unimodal condition. Primes and targets were from the same speaker (person‐congruent) or from two different speakers (person‐incongruent). Participants had to classify the S2 as either an old or a young person. Response times were shorter after a congruent than after an incongruent face prime. The right posterior superior temporal sulcus (pSTS) and the right angular gyrus showed a significant person identity effect (person‐incongruent > person‐congruent) in the crossmodal condition but not in the unimodal condition. In the unimodal condition, a person identity effect was observed in the bilateral inferior frontal gyrus. Our data suggest that both the priming with a voice and with a face result in a preactivated voice representation of the respective person, which eventually facilitates (person‐congruent trials) or hampers (person‐incongruent trials) the processing of the identity of a subsequent voice. This process involves activation in the right pSTS and in the right angular gyrus for voices primed by faces, but not for voices primed by voices. Hum Brain Mapp 38:2553–2565, 2017. © 2017 Wiley Periodicals, Inc.     

Sensory-specific satiety: Food-specific reduction in responsiveness of ventral forebrain neurons after feeding in the monkey

It has been shown previously that some neurons in the lateral hypothalamus and substantia innominata respond to the sight of food, others to the taste of food, and others to the sight or taste of food, in the hungry monkey. It is shown here that feeding to satiety decreases the responses of hypothalamic neurons to the sight and/or taste of a food on which the monkey has been satiated, but leaves the responses of the same neurons to other foods on which the monkey has not been satiated relatively unchanged. This suggests that the responses of these neurons in the ventral forebrain are related to sensory-specific satiety, an important phenomenon which regulates food intake. In sensory-specific satiety, the pleasantness of the sight or taste of a food becomes less after it is eaten to satiety, whereas the pleasantness of the sight or taste of other foods which have not been eaten is much less changed; correspondingly, food intake is greater if foods which have not already been eaten to satiety are offered.     

Neural mechanisms involved in odor pleasantness and intensity judgments

Olfactory processing in the human brain was examined using positron emission tomography. Twelve normal volunteers were scanned while smelling pairs of odors: they were asked to judge which odor was more pleasant in one condition, and which was more intense in a second condition; they also were scanned while sniffing an odorless stimulus. As in prior studies, greater cerebral blood flow was found in the right orbitofrontal cortex during both pleasantness and intensity judgments as compared to baseline. Cerebellar activity was also seen, but contrary to expectations no activity was detected in the primary olfactory (piriform) cortex. Only the pleasantness judgment elicited additional activity within the hypothalamus, suggesting that this structure may be involved in affective processing that requires access to information about internal state.     

Enhancement of Saltiness Perception in Hyperosmotic Solutions

Salt (sodium chloride) plays a major role in perception of flavor in food products. Though reducing sodium content in processed food could significantly improve the health level of the population, the detrimental change in flavor presents a major challenge as consumers generally find low salt products unacceptable. Therefore, technological solutions are being sought to lower the salt content of processed foods without altering their taste. In order to better understand saltiness perception in thickened products such as soups and sauces, this study was designed to evaluate the possibility of enhancing saltiness perception through use of hyperosmotic solutions containing high polymer concentration (up to 30%). Saltiness and sweetness perception were investigated in Newtonian solutions of identical viscosity thickened with different concentrations of dextran, which was achieved by using dextrans of different molecular weights. Attribute difference tests (paired comparisons and multiple paired comparisons) were performed by untrained subjects. A significant enhancement of saltiness, but not of sweetness, was found in hyperosmotic solutions (higher polymer concentration) compared to solutions of lower osmolality (lower polymer concentration). The present results may be considered as a human study validation of an in vitro demonstrated effect of osmolality on the response of taste receptor cells to NaCl and suggests that high concentrations of low molecular weight thickeners could be used to enhance saltiness perception in low salt products.     

Effect of Pulsed or Continuous Delivery of Salt on Sensory Perception Over Short Time Intervals

Salt in the human diet is a major risk factor for hypertension and many countries have set targets to reduce salt consumption. Technological solutions are being sought to lower the salt content of processed foods without altering their taste. In this study, the approach was to deliver salt solutions in pulses of different concentrations to determine whether a pulsed delivery profile affected sensory perception of salt. Nine different salt profiles were delivered by a Dynataste device and a trained panel assessed their saltiness using time–intensity and single-score sensory techniques. The profile duration (15 s) was designed to match eating conditions and the effects of intensity and duration of the pulses on sensory perception were investigated. Sensory results from the profiles delivered in either water or in a bouillon base were not statistically different. Maximum perceived salt intensities and the area under the time–intensity curves correlated well with the overall perceived saltiness intensity despite the stimulus being delivered as several pulses. The overall saltiness scores for profiles delivering the same overall amount of sodium were statistically not different from one another suggesting that, in this system, pulsed delivery did not enhance salt perception but the overall amount of salt delivered in each profile did affect sensory perception.     

Male Sexual Orientation Affects Sensitivity to Androstenone

Androstenone has often been discussed as a human social chemosignal, as it is one of the major contributing substances to the human body odor for which humans possess specific receptors. Here, we investigated whether male sexual orientation influences the perception of androstenone. Sensitivity to androstenone, subjective ratings of intensity, pleasantness, unpleasantness, and familiarity of the odor, as well as self-reported emotional responses (valence, arousal, dominance) to the odor were assessed in 13 homosexual and 14 heterosexual men. Isovaleric acid served as a control substance. Homosexual men displayed significantly higher olfactory sensitivity to the odor of androstenone than heterosexual men (p?<?0.05), but they did not differ from heterosexual men in their sensitivity to isovaleric acid (p?>?0.25). Moreover, both groups did not differ in their judgments of or in their emotional response to androstenone or isovaleric acid. The current results indicate that men's sexual orientation significantly impacts the perception of androstenone but that this effect does not necessarily extend to subjective judgments.     

Attenuation of auditory N1 results from identity‐specific action‐effect prediction

The auditory N1 event‐related potential has previously been observed to be attenuated for tones that are triggered by human actions. This attenuation is thought to be generated by motor prediction mechanisms and is considered to be important for agency attribution. The present study was designed to rigorously test the notion of action prediction‐based sensory attenuation. Participants performed one of four voluntary actions on each trial, with each button associated with either predictable or unpredictable action effects. In addition, actions with each hand could result in action effects that were either congruent or incongruent with hand‐specific prediction. We observed no significant differences in N1 amplitude between predictable and unpredictable tones. When contrasting action effects that were congruent or incongruent with hand‐specific prediction, we observed significant attenuation for prediction‐congruent compared to prediction‐incongruent action‐effects. These novel findings suggest that accurate action‐effect prediction drives sensory attenuation of auditory stimuli. These findings have important implications for understanding the mechanisms of action‐effect prediction and sensory attenuation, and may have clinical implications for studies investigating action awareness and agency in schizophrenia.