Differences in the central-nervous processing of olfactory stimuli according to their hedonic and arousal characteristics

Functional septorhinoplasty alters brain structure and function: Neuroanatomical correlates of olfactory dysfunction

Introduction

We previously demonstrated functionally significant structural plasticity within the central olfactory networks, in association with improved olfaction after surgical treatment of chronic rhinosinusitis (CRS). In order to confirm and expand on these findings, the primary aim of this study was to determine whether these same regions undergo functionally significant structural plasticity following functional septorhinoplasty (fSRP), in patients with non-CRS olfactory dysfunction (OD) of mixed cause. fSRP has previously been shown to improve olfactory function, and the secondary aim of this study was to provide initial insights into the mechanism by which fSRP affects olfaction.

Methods

We performed a pilot prospective, multimodal neuroimaging study in 20 participants undergoing fSRP, including patients with non-CRS OD of mixed cause, as well as normosmic surgical controls. Participants underwent psychophysical olfactory testing, assessment of nasal airway, structural and functional neuroimaging. This was performed pre- and postoperatively in patients, and preoperatively in controls.

Results

There was a statistically and clinically significant improvement in mean psychophysical olfactory scores after surgery. This was associated with structural and functional plasticity within areas of the central olfactory network (anterior cingulate, orbitofrontal cortex, insula, temporal pole). Improved psychophysical scores were significantly correlated with change in bilateral measures of nasal airflow, not measures of airflow symmetry, suggesting that improved overall airflow was more important than correction of septal deviation.

Conclusion

This work highlights the importance of these neuroanatomical regions as potential structural correlates of olfactory function and dysfunction. Our results also provide initial insight into the mechanistic effects of fSRP on olfaction. Further work could investigate the utility of these regions as personalised biomarkers of OD, as well as the role of fSRP in treating OD.

Patterns of Gray and White Matter Volume Alterations in Patients With Post-Traumatic Anosmia: A Voxel-Based Morphometry Study

Objective

Traumatic brain injury is one of the major causes of human olfactory dysfunction and leads to brain structure alterations, mainly in the cortical olfactory regions. Our study aimed to investigate volume changes in the gray matter (GM) and white matter (WM) in patients with post-traumatic anosmia and then to explore the relationship between GM volume and olfactory function.

Methods

Ethics committee approved prospective studies which included 22 patients with post-traumatic anosmia and 18 age- and gender-matched healthy volunteers. Olfactory function was assessed using the Sniffin' Sticks. High-resolution 3-dimensional T1 MRIs of the participants were acquired on a 3T scanner and the data were collected for voxel-based morphometry (VBM) analysis. Furthermore, the GM and WM volumes of the whole brain regions were compared and correlated with olfactory function.

Results

The analysis revealed significant GM volume reduction in the orbitofrontal cortex (OFC), gyrus rectus (GR), olfactory cortex, insula, parahippocampal, temporal pole, and cerebellum (all P < 0.001) in patients. Besides, WM volume loss was also found in the OFC, GR, and insula (all P < 0.001) in patients. All WM atrophy areas were connected to areas of GM volume loss spatially. Correlation analysis showed the olfactory scores were significantly positively correlated with the GM volume of the occipital cortex (P < 0.001, and PFWE < 0.05), while no significant correlation was found between the Sniffin' Sticks test scores and the WM volume in patients.

Conclusion

The reduction of GM and WM volume in olfactory-related regions was responsible for olfactory dysfunction in post-traumatic patients. The occipital cortex may play a compensation mechanism to maintain the residual olfactory function. To our knowledge, we report here for the first time on white matter volume alterations specifically in post-traumatic patients with anosmia.

Unpleasant Odors Affect Alerting Attention in Young Men: An Event-Related Potential Study Using the Attention Network Test

Attention to unpleasant odors is crucial for human safety because they may signal danger; however, whether odor concentration also plays a role remains debated. Here, we explored the effects of two concentrations of pleasant and unpleasant odors on the attention network, comprising the alerting, orienting, and executive control networks. Behavioral responses were examined using the Attention Network Test, while electrophysiological responses were examined by assessing N1 and N2 amplitudes in 30 young men. We found that irrespective of odor concentration, an unpleasant odor induced larger cue-related N1 and N2 amplitudes in the alerting and executive control networks at occipital and frontal electrode sites and that was only paralleled by a reduced behavioral response time of cue-related trails in the alerting network. Thus, our results do not provide supporting evidence for a concentration-dependent effect, but they do suggest that more attentional resources are allocated to alerting-relevant stimuli to improve behavioral response times to a potential threat in young men.

Olfactory Modulation of the Contingent Negative Variation to Auditory Stimuli

Although pleasantness is intrinsically related to the perception of odors it is difficult to objectively assess odor-induced pleasantness. To evaluate the effects of odors of different valences on the contingent negative variation (CNV) in a younger and an older population. Data from 62 participants (27 men, 35 women) were included. Two age groups with Age group 1 (YOUNG) had 30 subjects within age 18-30 years and age group 2 (OLD) had 32 subjects with age >40 years. Pre-testing was performed to acquaint subjects with the experimental tasks and their environment. Subjects received "Sniffin' Sticks" odor identification tests and a standardized medical history to ascertain normosmia. In addition, they also took questionnaires relating to importance of the sense of smell and personality traits. CNV was elicited with two auditory stimuli, S1 followed by S2 at an interval of 2.4 s. Subjects were asked to push a button as fast as possible after they perceived S2. EEG was recorded from 4 positions of the 10-20 system (Fp2, Fz, Cz, and Pz). Four odors plus odorless air was presented in randomized order. The following main results emerged: (1) Consistent with the literature CNV showed a typical topographical distribution with the largest amplitude over the front-central recording sites. (2) 69% of subjects had consistent CNV for all conditions. (3) for some odor conditions CNV amplitudes exhibit a weak relation to odor pleasantness and associations with calmness. (4) CNV amplitude correlated negatively with reaction times. Overall, the results suggest the usefulness of CNV as an electrophysiological measure of cognition. However, in the present context, concomitantly applied odors of different hedonic tones exerted only minor effects on CNV. Thus, we conclude that odors have little or no effect on CNV.

Reorganizing brain structure through olfactory training in post-traumatic smell impairment: An MRI study

PURPOSE AND BACKGROUND

Post-traumatic olfactory dysfunction (PTOD), mostly caused by head injury, is thought to be associated with changes in the structure and function of the brain olfactory processing areas. Training and repeated exposure to odorants lead to enhanced olfactory capability. This study investigated the effects of a 16-weeks olfactory training (OT) on olfactory function and brain structure.

METHODS

Twenty-five patients with PTOD were randomly divided in three groups: (1) 9 control patients who did not receive any training, (2) 9 patients underwent classical OT by 4 fixed odors, and (3) 7 patients underwent modified OT coming across 4 sets of 4 different odors sequentially. Before and after the training period, all patients performed olfactory function tests and structural magnetic resonance imaging (MRI). Sniffin' Sticks test was used to assess olfactory function. MRI data were analyzed using voxel-based morphometry and surface-based morphometry.

RESULTS

Both trained groups showed a considerable recovery of olfactory function, especially in odor identification. MRI data analysis revealed that the classical OT leads to increases in cortical thickness/density of several brain regions, including the right superior and middle frontal gyrus, and bilateral cerebellums. In addition, the modified OT yielded a lower extent of cortical measures in the right orbital frontal cortex and right insular. Following modified OT, a positive correlation was observed between the odor identification and the right orbital frontal cortex.

CONCLUSION

Both olfactory training methods can improve olfactory function and that the improvement is associated with changes in the structure of olfactory processing areas of the brain.

Validation of Olfactory Network Based on Brain Structural Connectivity and Its Association With Olfactory Test Scores

Olfactory perception is a complicated process involving multiple cortical and subcortical regions, of which the underlying brain dynamics are still not adequately mapped. Even in the definition of the olfactory primary cortex, there is a large degree of variation in parcellation templates used for investigating olfaction in neuroimaging studies. This complicates comparison between human olfactory neuroimaging studies. The present study aims to validate an olfactory parcellation template derived from both functional and anatomical data that applies structural connectivity (SC) to ensure robust connectivity to key secondary olfactory regions. Furthermore, exploratory analyses investigate if different olfactory parameters are associated with differences in the strength of connectivity of this structural olfactory fingerprint. By combining diffusion data with an anatomical atlas and advanced probabilistic tractography, we found that the olfactory parcellation had a robust SC network to key secondary olfactory regions. Furthermore, the study indicates that higher ratings of olfactory significance were associated with increased intra- and inter-hemispheric SC of the primary olfactory cortex. Taken together, these results suggest that the patterns of SC between the primary olfactory cortex and key secondary olfactory regions has potential to be used for investigating the nature of olfactory significance, hence strengthening the theory that individual differences in olfactory behaviour are encoded in the structural network fingerprint of the olfactory cortex.

Insula and Olfaction: A Literature Review and Case Report

(1) Background: It is well established that the insula is involved in olfaction, though its specific role in olfactory processing remains uncertain. In this paper, we first review the current literature on the insula and olfaction. Then, we describe the case of a 56-year-old man with a left insular cavernoma that caused olfactory disturbances. (2) Results: Structural neuroimaging studies suggest that insular gray matter volume is related to olfactory function, and functional neuroimaging shows that various types of stimuli lead to either lateralized or bilateral insular activations. Studies using electro-cortical stimulation reveal a specific region of the insular cortex, around the central insular sulcus, that could be related to unpleasant odor processing. Previous cases of insular lesions leading to olfactory disturbances suggest that left-sided insular lesions may more frequently lead to olfactory changes. In our patient with a left insular cavernoma, odors that were previously perceived as pleasant started smelling unpleasant and were hard to distinguish. Despite these subjective complaints, olfactory function assessed with the Sniffin’ Sticks test was normal. (3) Conclusions: Current tests may not be sensitive to all types of olfactory impairments associated with insular damage, and further studies should be conducted to develop olfactory tests assessing the hedonic appreciation of odors.

Individual odor hedonic perception is coded in temporal joint network activity

INTRO

The human sense of smell is highly individual and characterized by a strong variability in the perception and evaluation of olfactory stimuli, depending on cultural imprint and current physiological conditions. Since this individual perspective has often been neglected in fMRI studies on olfactory hedonic coding, this study focuses on the neuronal activity and connectivity patterns resulting from subject-specific olfactory stimulation.

METHODS

Thirty-one normosmic participants took part in a fMRI block designed paradigm consisting of three olfactory stimulation sessions. The most pleasant and unpleasant odors were individually specified during a pre-test for each participant and validated in the main experiment. Mean activation and functional connectivity analysis focusing on the right and left piriform cortex were performed for the predefined olfactory regions-of-interest (ROIs) and compared between the three olfactory conditions.

RESULTS

Individual unpleasant olfactory stimulation as compared to pleasant or neutral did not alter mean BOLD activation in the predefined olfactory ROIs but led to a change in connectivity pattern in the right piriform cortex.

CONCLUSION

Our data suggests that the individual pleasantness of odors is not detectable by average BOLD magnitude changes in primary or secondary olfactory brain areas, but reflected in temporal patterns of joint activation that create a network between the right piriform cortex, the left insular cortex, the orbitofrontal cortex, and the precentral gyrus. This network may serve the evolutionary defense mechanism of olfaction by preparing goal-directed action.

Valence Encoding Signals in the Human Amygdala and the Willingness to Eat

One of the strongest drivers of food consumption is pleasure, and with a large variety of palatable food continuously available, there is rarely any necessity to eat something not tasty. The amygdala is involved in hedonic valuation, but its role in valence assignment during food choices is less understood. Given recent evidence for spatially segregated amygdala signatures encoding palatability, we applied a multivariate approach on fMRI data to extract valence-specific signal patterns during an explicit evaluation of food liking. These valence localizers were then used to identify hedonic valuation processes while the same healthy human participants (14 female, 16 male; in overnight fasted state on both scanning days) performed a willingness-to-eat task in a separate fMRI measurement. Valence-specific patterns of amygdala signaling predicted decisions on food consumption significantly. Findings could be validated using the same valence localizers to predict consumption decisions participants made on a separate set of food stimuli that had not been used for localizer identification. Control analyses revealed these findings to be restricted to a multivariate compared with a univariate approach, and to be specific for valence processing in the amygdala. Spatially distributed valuation signals of the amygdala thus appear to modulate appetitive consumption decisions, and may be useful to identify current hedonic valuation processes triggering food choices even when not explicitly instructed.SIGNIFICANCE STATEMENT The expectation of tastiness is a particularly strong driver in everyday decisions on food consumption. The amygdala is important for hedonic valuation processes and involved in valence-related behavior, but the relationship between both processes is less understood. Here, we show that hedonic values of food are represented in spatially distributed activation patterns in the amygdala. The engagement of these patterns during food choices modulates consumption decisions. Findings are stable in a separate stimulus set. These results suggest that valence-specific amygdala signals are integrated into the formation of food choices.

Behavioral and Neurobiological Convergence of Odor, Mood and Emotion: A Review

The affective state is the combination of emotion and mood, with mood reflecting a running average of sequential emotional events together with an underlying internal affective state. There is now extensive evidence that odors can overtly or subliminally modulate mood and emotion. Relying primarily on neurobiological literature, here we review what is known about how odors can affect emotions/moods and how emotions/moods may affect odor perception. We take the approach that form can provide insight into function by reviewing major brain regions and neural circuits underlying emotion and mood, and then reviewing the olfactory pathway in the context of that emotion/mood network. We highlight the extensive neuroanatomical opportunities for odor-emotion/mood convergence, as well as functional data demonstrating reciprocal interactions between these processes. Finally, we explore how the odor- emotion/mood interplay is, or could be, used in medical and/or commercial applications.

Central olfactory structures

Axons from the olfactory bulb (OB) project to multiple central structures of the brain, many of which, in turn, send axons back into the OB and/or to one another. These secondary sensory regions underlie many aspects of odor representation, valence, and learning, as well as serving some nonolfactory functions, though many details remain unclear. We here describe the connectivity and essential structural and functional properties of these postbulbar olfactory regions in the mammalian brain.

Odor-induced emotion recognition based on average frequency band division of EEG signals

BACKGROUND

Emotion recognition plays a key role in multimedia. To enhance the sensation of reality, smell has been incorporated into multimedia systems because it can directly stimulate memories and trigger strong emotions.

NEW METHOD

For the recognition of olfactory-induced emotions, this study explored a combination method using a support vector machine (SVM) with an average frequency band division (AFBD) method, where the AFBD method was proposed to extract the power-spectral-density (PSD) features from electroencephalogram (EEG) signals induced by smelling different odors. The so-called AFBD method means that each PSD feature was calculated based on equal frequency bandwidths, rather than the traditional EEG rhythm-based bandwidth. Thirteen odors were used to induce olfactory EEGs and their corresponding emotions. These emotions were then divided into two types of emotions, pleasure and disgust, or five types of emotions that were very unpleasant, slightly unpleasant, neutral, slightly pleasant, and very pleasant.

RESULTS

Comparison between the proposed SVM plus AFBD method and other methods found average accuracies of 98.9 % and 88.5 % for two- and five-emotion recognition, respectively. These values were considerably higher than those of other combination methods, such as the combinations of AFBD or EEG rhythm-based features with naive Bayesian, k-nearest neighbor classification, voting-extreme learning machine, and backpropagation neural network methods.

CONCLUSIONS

The SVM plus AFBD method represents a useful contribution to olfactory-induced emotion recognition. Classification of the five-emotion categories was generally inferior to the classification of the two-emotion categories, suggesting that the recognition performance decreased as the number of emotions in the category increased.

Emotional and Autonomic Processing of Olfactory Stimuli Is Compromised in Patients with a History of Mild Traumatic Brain Injury

Patients with a history of mild traumatic brain injury (post-mTBI patients) may have enduring cardiovascular-autonomic dysregulation and emotional problems. Olfactory stimulation (OS) triggers emotional and cardiovascular-autonomic responses that might be compromised in post-mTBI patients. We therefore evaluated these responses to OS in post-mTBI patients. In 17 post-mTBI patients (interval since mTBI: 32.4 ± 6.8 months) and 17 age- and sex-matched controls, we recorded respiration, electrocardiographic RR intervals, and systolic and diastolic blood pressures (BPsys, BPdia) before and during pleasant vanilla stimulation and unpleasant hydrogen sulphide (H2S) stimulation. Participants rated OS-related pleasantness, arousal, intensity, and familiarity on 9-point Likert scales. Analyses of variance (ANOVAs) with post hoc analyses compared parameters within each group before and during OS. To assess associations between pleasantness, arousal, intensity, and familiarity, we correlated OS scores within groups (significance: p < 0.05). Baseline parameters were similar between groups. Only in controls, vanilla stimulation significantly lowered BPsys and BPdia, whereas H2S stimulation lowered RR intervals. Vanilla-related pleasantness scores were lower, intensity scores were higher in patients than controls. During vanilla stimulation, pleasantness scores correlated negatively with arousal scores in controls, whereas familiarity scores correlated positively with intensity scores in patients. During H2S stimulation, familiarity scores correlated negatively with pleasantness scores in controls, whereas pleasantness scores correlated negatively with arousal scores in mTBI patients. Post-mTBI patients could not change BP or RR intervals during OS but perceived vanilla stimuli as less pleasant and more intense than did controls. Associations between pleasantness, arousal, intensity, and familiarity differed between groups suggesting different activation of the olfactory network and the central autonomic network upon OS. Subtle lesions within these networks might cause persistent changes in emotional and cognitive odor perception and cardiovascular responses.

Odor perception and hedonics in chronic schizophrenia and in first episode psychosis

BACKGROUND AND PURPOSE

The study evaluated olfactory performance and pleasantness rating of odors in patients with first episode psychosis (FEP) and chronic schizophrenia (SCH) with regard to the severity of psychopathological symptoms and plasma β-endorphin concentration.

PATIENTS AND METHODS

Twenty patients with FEP, 27 with SCH and 29 healthy individuals, were recruited to the research . The University of Pennsylvania Smell Identification Test (UPSIT), subjective odor hedonic judgment and plasma levels of β-endorphin (BE) assay were performed in all participants.

RESULTS

Individuals with SCH revealed higher BE concentration than other study groups (P=0.000). All patients identified pleasant odors poorer than controls, however, SCH made more identification errors (P=0.000) than those with FEP. Moreover, participants with FEP rated pleasant odors as more pleasant than individuals with chronic schizophrenia and healthy controls (P=0.009). Nevertheless, higher β-endorphin level was related with lower scores in pleasant odor identification (Rs=-0.452; P=0.046) and more severe psychotic symptoms in FEP sample. Chronic schizophrenia patients did not demonstrate any relationship between symptom severity, odor identification performance and β-endorphin concentration. No relationship was found between BE concentration and hedonic judgment of the presented odors among all study groups. Chronically ill subjects identified odors significantly more poorly than those with first episode psychosis. Deficits in identifying pleasant odors might not be the only potential risk factor for undergoing chronic, recurrent schizophrenia. All patients subjectively overrated pleasant odors. Those with SCH and more severe negative symptoms made significantly more identification errors.

CONCLUSION

The endogenous morphine system deregulation is observed in first episode psychosis as well as in chronic schizophrenia. In first episode schizophrenia higher beta-endorphin concentration is related to pleasant odor identification deficit.

Diminished positive affect and traumatic stress: A biobehavioral review and commentary on trauma affective neuroscience

Post-traumatic stress manifests in disturbed affect and emotion, including exaggerated severity and frequency of negative valence emotions, e.g., fear, anxiety, anger, shame, and guilt. However, another core feature of common post-trauma psychopathologies, i.e. post-traumatic stress disorder (PTSD) and major depression, is diminished positive affect, or reduced frequency and intensity of positive emotions and affective states such as happiness, joy, love, interest, and desire/capacity for interpersonal affiliation. There remains a stark imbalance in the degree to which the neuroscience of each affective domain has been probed and characterized in PTSD, with our knowledge of post-trauma diminished positive affect remaining comparatively underdeveloped. This remains a prominent barrier to realizing the clinical breakthroughs likely to be afforded by the increasing availability of neuroscience assessment and intervention tools. In this review and commentary, the author summarizes the modest extant neuroimaging literature that has probed diminished positive affect in PTSD using reward processing behavioral paradigms, first briefly reviewing and outlining the neurocircuitry implicated in reward and positive emotion and its interrelationship with negative emotion and negative valence circuitry. Specific research guidelines are then offered to best and most efficiently develop the knowledge base in this area in a way that is clinically translatable and will exert a positive impact on routine clinical care. The author concludes with the prediction that the development of an integrated, bivalent theoretical and predictive model of how trauma impacts affective neurocircuitry to promote post-trauma psychopathology will ultimately lead to breakthroughs in how trauma treatments are conceptualized mechanistically and developed pragmatically.

Food-Related Odors Activate Dopaminergic Brain Areas

Food-associated cues of different sensory categories have often been shown to be a potent elicitor of cerebral activity in brain reward circuits. Smells influence and modify the hedonic qualities of eating experience, and in contrast to smells not associated with food, perception of food-associated odors may activate dopaminergic brain areas. In this study, we aimed to verify previous findings related to the rewarding value of food-associated odors by means of an fMRI design involving carefully preselected odors of edible and non-edible substances. We compared activations generated by three food and three non-food odorants matching in terms of intensity, pleasantness and trigeminal qualities. We observed that for our mixed sample of 30 hungry and satiated participants, food odors generated significantly higher activation in the anterior cingulate cortex (right and left), insula (right), and putamen (right) than non-food odors. Among hungry subjects, regardless of the odor type, we found significant activation in the ventral tegmental area in response to olfactory stimulation. As our stimuli were matched in terms of various perceptual qualities, this result suggests that edibility of an odor source indeed generates specific activation in dopaminergic brain areas.