Combining electrodermal activity analysis and dynamic causal modeling to investigate the visual-odor multimodal integration during face perception.

Objective. This study presents a novel methodological approach for incorporating information related to the peripheral sympathetic response into the investigation of neural dynamics. Particularly, we explore how hedonic contextual olfactory stimuli influence the processing of neutral faces in terms of sympathetic response, event-related potentials and effective connectivity analysis. The objective is to investigate how the emotional valence of odors influences the cortical connectivity underlying face processing and the role of face-induced sympathetic arousal in this visual-olfactory multimodal integration.Approach. To this aim, we combine electrodermal activity (EDA) analysis and dynamic causal modeling to examine changes in cortico-cortical interactions.Results. The results reveal that stimuli arising sympathetic EDA responses are associated with a more negative N170 amplitude, which may be a marker of heightened arousal in response to faces. Hedonic odors, on the other hand, lead to a more negative N1 component and a reduced the vertex positive potential when they are unpleasant or pleasant. Concerning connectivity, unpleasant odors strengthen the forward connection from the inferior temporal gyrus (ITG) to the middle temporal gyrus, which is involved in processing changeable facial features. Conversely, the occurrence of sympathetic responses after a stimulus is correlated with an inhibition of this same connection and an enhancement of the backward connection from ITG to the fusiform face gyrus.Significance. These findings suggest that unpleasant odors may enhance the interpretation of emotional expressions and mental states, while faces capable of eliciting sympathetic arousal prioritize identity processing.

Alexithymia modulates the attitudes towards odors but not the olfactory abilities or the affective reactions to odors.

Although emotion and olfaction are closely linked, only a few studies have investigated olfactory processing in alexithymia, a condition characterized by altered emotional processing. These results do not allow comprehensive conclusions on whether individuals with alexithymia present lower olfactory abilities or only altered affective reactions and awareness of odors. Three pre-registered experiments were conducted to clarify this relation. We assessed olfactory functions, the affective qualities of odors, the awareness of odors, the attitudes towards them, and the ability to form olfactory images in the mind. Bayesian statistics were used to assess differences between low, medium and high alexithymia groups, and Linear Mixed Models (LMMs) were applied to investigate the modulation of the affective and cognitive components of alexithymia. We observed that individuals with a high level of alexithymia presented the same olfactory abilities, and did not show differences in their rating of odors compared to individuals with low alexithymia levels, while they reported lower levels of social and common odor awareness and a more indifferent attitude towards odors. Olfactory imagery was not affected by alexithymia level, and the affective and cognitive components of alexithymia, when considered separately, modulated olfactory perception differently. Learning more about olfactory perception in individuals with alexithymia leads to a better understanding of how alexithymia impacts the perception of hedonic stimuli coming from different sensory modalities. Our results imply that treatment goals for alexithymia should be the enhancement of the conscious perception of odors, supporting the use of mindfulness-based protocols in the alexithymia treatment.

Low odor awareness predicts reduced olfactory abilities in women with depressive symptoms, but not with anxiety symptoms.

BACKGROUND: Olfactory disorders and affective symptoms are tightly related. However, the factors underlying this association are not yet understood. One candidate factor is "odor awareness": the degree of attention individuals pays to the odors. However, the association between odor awareness and olfactory abilities in individuals with affective symptoms has not been clarified yet. METHOD: The present study examined whether odor awareness may moderate (a) the relation between olfactory dysfunctions and depressive and anxiety symptoms; (b) the relation between the perceptual ratings of the odors and depressive and anxiety symptoms in a sample of healthy women (n = 214). Self-report measures of depression and anxiety were collected, whereas the Sniffin' Stick test was employed to measure olfactory abilities. RESULTS: Linear regression analysis revealed that individuals with higher depressive symptoms presented lower olfactory abilities and that odor awareness was a significant moderator of the association between depressive symptoms and olfactory abilities. Anxiety symptoms were not related to any of the olfactory abilities considered, and this relationship did not change according to odor awareness. The familiarity rating of the odor was significantly predicted by odor awareness. These results were confirmed by Bayesian statistics. LIMITATIONS: The sample was composed only of women. CONCLUSIONS: In a healthy population of women, only the presence of depressive symptoms is related to reduced olfactory performance. Odor awareness may be implicated in the development and maintenance of olfactory dysfunction; hence it could be used as a useful target for specific treatments in clinical settings.

Human body odors of happiness and fear modulate the late positive potential component during neutral face processing: a preliminary ERP study on healthy subjects.

Human body odors (HBOs) are powerful stimuli that can affect emotional, cognitive and behavioral processes. However, the characterization of the physiological response to HBOs is still to be fully investigated. Here, we analyzed the self-assessed emotion perception and the EEG event-related potentials (ERP) on 17 healthy young women during a simultaneous visual-olfactory stimulation. Particularly, we evaluated the effect of happiness and fear HBO on the amplitude of ERP waveforms elicited by neutral face processing. In addition, we evaluated the subjective valence and arousal perception of the presented neutral faces by means of the self-assessment-manikin test. We observed a significant increase in the amplitude of the late positive potential (LPP) for central left sites (i.e., C3) during the administration of HBOs with respect to clean air. On the other hand, we did not observe any significant change in the subjective valence and arousal scores as well as for the early components of the ERP (i.e., P100, N170, Vertex-Positive-Potential). Our preliminary results suggest that fear and happiness HBO can induce a protracted increase in the LPP, and possibly reflect an automatic and sustained engagement with emotionally significant content.

Future Directions for Chemosensory Connectomes: Best Practices and Specific Challenges.

Ecological chemosensory stimuli almost always evoke responses in more than one sensory system. Moreover, any sensory processing takes place along a hierarchy of brain regions. So far, the field of chemosensory neuroimaging is dominated by studies that examine the role of brain regions in isolation. However, to completely understand neural processing of chemosensation, we must also examine interactions between regions. In general, the use of connectivity methods has increased in the neuroimaging field, providing important insights to physical sensory processing, such as vision, audition, and touch. A similar trend has been observed in chemosensory neuroimaging, however, these established techniques have largely not been rigorously applied to imaging studies on the chemical senses, leaving network insights overlooked. In this article, we first highlight some recent work in chemosensory connectomics and we summarize different connectomics techniques. Then, we outline specific challenges for chemosensory connectome neuroimaging studies. Finally, we review best practices from the general connectomics and neuroimaging fields. We recommend future studies to develop or use the following methods we perceive as key to improve chemosensory connectomics: (1) optimized study designs, (2) reporting guidelines, (3) consensus on brain parcellations, (4) consortium research, and (5) data sharing.

Olfactory meta-cognition in individuals with depressive and anxiety symptoms: The differential role of common and social odors.

BACKGROUND: Diminished olfactory functioning has been reported in depression, whereas evidence in anxiety disorders is still controversial. Olfactory meta-cognitive abilities (i.e., olfactory awareness, imagery and reactivity, and the importance of odors) are essential in shaping olfaction. Few studies examined these meta-cognitive abilities in relation to depressive, anxiety, and social anxiety symptoms, and none of them considered the awareness of social odors (i.e., body odors). METHODS: This pre-registered study examined the relationship between olfactory meta-cognitive abilities and symptoms of depression, general anxiety, and social anxiety in 429 individuals. Self-report measures of symptoms of depression, general anxiety, and social anxiety, along with self-report olfactory meta-cognitive scales, were collected using an online survey. RESULTS: Linear regression analyses revealed that olfactory awareness and importance of common odors were significantly directly predicted by symptoms of general anxiety, while affective importance to odors was negatively predicted by symptoms of depression. Regarding social odors, higher symptoms of depression and lower symptoms of social anxiety predicted increased awareness. LIMITATIONS: Higher prevalence of women and narrow age range of the participants. Depressive and anxiety symptoms were assessed only with self-report questionnaires. CONCLUSIONS: Symptoms of anxiety seem to be associated with higher levels of common odor awareness, corroborating the importance of olfactory functions in anxiety. In addition, results on social odors seem to reflect dysfunctional social behaviour that characterized symptoms of depression and social anxiety. Hence, the assessment of meta-cognitive abilities may represent a useful tool in the prevention and assessment of depressive, anxiety, and social anxiety symptoms.

The social odor scale: Development and initial validation of a new scale for the assessment of social odor awareness.

The degree of attention individuals pay to olfactory cues (called odor awareness) influences the role of odors in everyday life. Particularly, odors produced by the human body (i.e., social odors) are able to carry a wide variety of information and to elicit a broad spectrum of emotional reactions, making them essential in interpersonal relationships. Hence, despite the assessment of awareness toward social odors is crucial, a proper tool is still lacking. Here, we designed and initially validated the Social Odor Scale (SOS), a 12-item scale designed to measure the individual differences in awareness towards different social odors. In Study 1, an exploratory factor analysis (EFA; KMO test: MSA = 0.78; Bartlett's test: χ2(78) = 631.34, p < 0.001; Chi-squared test: χ2(42) = 71.84, p = 0.003) suggests that the three factors structure was the model that best fit with the Italian version of the scale. The confirmatory factor analysis (CFA) supports a second-order model with one higher-order factor representing social odor awareness in general and three lower-order factors representing familiar, romantic partner, and stranger social odors. The final version of the scale presented a good fit (RMSEA = 0.012, SRMR = 0.069, CFI = 0.998, TLI = 0.997). In Study 2, CFA was performed in the German version of the scale confirming the validity of scale structure. Study 3 and 4 revealed that SOS total score and its subscales were positively correlated with other validated olfactory scales, but not with olfactory abilities. Moreover, SOS was found to be related to the gender of the participants: women reported to be more aware to social odors and, specifically, to familiar social odors than men. Overall, the results indicated that SOS is a valid and reliable instrument to assess awareness toward social odors in everyday life.

Assessing the extent and timing of chemosensory impairments during COVID-19 pandemic.

Chemosensory impairments have been established as a specific indicator of COVID-19. They affect most patients and may persist long past the resolution of respiratory symptoms, representing an unprecedented medical challenge. Since the SARS-CoV-2 pandemic started, we now know much more about smell, taste, and chemesthesis loss associated with COVID-19. However, the temporal dynamics and characteristics of recovery are still unknown. Here, capitalizing on data from the Global Consortium for Chemosensory Research (GCCR) crowdsourced survey, we assessed chemosensory abilities after the resolution of respiratory symptoms in participants diagnosed with COVID-19 during the first wave of the pandemic in Italy. This analysis led to the identification of two patterns of chemosensory recovery, partial and substantial, which were found to be associated with differential age, degrees of chemosensory loss, and regional patterns. Uncovering the self-reported phenomenology of recovery from smell, taste, and chemesthetic disorders is the first, yet essential step, to provide healthcare professionals with the tools to take purposeful and targeted action to address chemosensory disorders and their severe discomfort.

Metabolic Dynamics in the Prefrontal Cortex during a Working Memory Task in Young Adult Smokers.

INTRODUCTION: Cigarette smoking is known to modulate brain metabolism and brain function. How the dynamics of these metabolic alterations influence the active performance of higher order cognitive tasks in smokers, compared to non-smokers, is still unclear. The present exploratory study sought to examine the impact of smoking on the "complete" metabolic profile while the participants performed a working memory (N-back) task. METHODS: The study sample consisted of 40 young male healthy participants (smokers [n = 20] and non-smokers [n = 20]). Functional magnetic resonance spectroscopy data were acquired using a 3 T whole-body MR system. Data analysis was performed using Java-based Magnetic Resonance User Interface software, and metabolite ratios with respect to creatine (Cr) were calculated. RESULTS: On a behavioural level, smokers showed worse performance (measured by d') than non-smokers. However, we observed significant differences in the metabolite concentrations in smokers compared to non-smokers, which also changed over the course of the N-back task. A significant effect of the group was observed with smokers showing lower glutamate/Cr (Glx/Cr) and choline/Cr (Cho/Cr) ratios than non-smokers. Further, N-acetyl aspartate (NAA/Cr) and Cho/Cr ratios were significantly different during the rest and the task conditions. In addition, our results demonstrated the metabolite interactions (NAA and Cho, Glx and myo-inositol [mI], and Cho and mI). CONCLUSION: Further studies are necessary to shed more light on the association between smoking behaviours and metabolic alterations. However, our preliminary findings would assist in this future research to have a complete understanding of the metabolite interactions not only in smoking but also in addiction research.

From loss to recovery: how to effectively assess chemosensory impairments during COVID-19 pandemic.

Chemosensory impairments have been established as a specific indicator of COVID-19. They affect most patients and may persist long past the resolution of respiratory symptoms, representing an unprecedented medical challenge. Since the SARS-CoV-2 pandemic started, we now know much more about smell, taste, and chemesthesis loss associated with COVID-19. However, the temporal dynamics and characteristics of recovery are still unknown. Here, capitalizing on data from the Global Consortium for Chemosensory Research (GCCR) crowdsourced survey, we assessed chemosensory abilities after the resolution of respiratory symptoms in participants diagnosed with COVID-19 during the first wave of the pandemic in Italy. This analysis led to the identification of two patterns of chemosensory recovery, limited (partial) and substantial, which were found to be associated with differential age, degrees of chemosensory loss, and regional patterns. Uncovering the self-reported phenomenology of recovery from smell, taste, and chemesthetic disorders is the first, yet essential step, to provide healthcare professionals with the tools to take purposeful and targeted action to address chemosensory disorders and its severe discomfort.

The Influence of Personality, Resilience, and Alexithymia on Mental Health During COVID-19 Pandemic.

Following the COVID-19 pandemic, many countries worldwide have put lockdowns in place to prevent the virus from spreading. Evidence shows that lockdown measures can affect mental health; it is, therefore, important to identify the psychological characteristics making individuals more vulnerable. The present study aimed, first, to identify, through a cluster analysis, the psychological attributes that characterize individuals with similar psychological responses to the COVID-19 home confinement; second, to investigate whether different psychological characteristics, such as personality traits, alexithymia, and resilience, specifically influence anxiety, stress, and depression, depending on the scope of the confinement. We analyzed data from 393 participants who completed an online survey on their experiences during two different phases of the Italian lockdown, characterized by more or less strict measures of confinement. Two clusters were identified which included participants reporting a better (+ER) and worse (-ER) emotional response to the lockdown, respectively. Individuals in the -ER group showed lower emotional stability, resilience, and higher alexithymia. Moreover, even if lifting part of the restrictions decreased psychological distress among all participants, a reduction in perceived stress was observed only among individuals with high resilience. Finally, personality traits, alexithymia, and resilience differently affected depression, anxiety, and stress. Our results suggest that different psychological interventions should be planned depending on the context: mental health professionals should focus on enhancing the individuals' coping strategies to alleviate stress in emergencies, while long-term intervention aiming at alleviating anxiety and depressive symptoms should focus on alexithymic tendencies and personality constructs.

Increased emotional eating during COVID-19 associated with lockdown, psychological and social distress.

Due to the spread of COVID 2019, the Italian government imposed a lockdown on the national territory. Initially, citizens were required to stay at home and not to mix with others outside of their household (Phase 1); eventually, some of these restrictions were lifted (Phase 2). To investigate the impact of lockdown on emotional and binge eating, an online survey was conducted to compare measures of self-reported physical (BMI), psychological (Alexithymia), affective (anxiety, stress, and depression) and social (income, workload) state during Phase 1 and Phase 2. Data from 365 Italian residents showed that increased emotional eating was predicted by higher depression, anxiety, quality of personal relationships, and quality of life, while the increase of bingeing was predicted by higher stress. Moreover, we showed that higher alexithymia scores were associated by increased emotional eating and higher BMI scores were associated with both increased emotional eating and binge eating. Finally, we found that from Phase 1 to Phase 2 binge and emotional eating decreased. These data provide evidence of the negative effects of isolation and lockdown on emotional wellbeing, and, relatedly, on eating behaviour.

Human Chemosignals and Brain Activity: A Preliminary Meta-analysis of the Processing of Human Body Odors.

Across phyla, chemosignals are a widely used form of social communication and increasing evidence suggests that chemosensory communication is present also in humans. Chemosignals can transfer, via body odors, socially relevant information, such as specific information about identity or emotional states. However, findings on neural correlates of processing of body odors are divergent. The aims of this meta-analysis were to assess the brain areas involved in the perception of body odors (both neutral and emotional) and the specific activation patterns for the perception of neutral body odor (NBO) and emotional body odor (EBO). We conducted an activation likelihood estimation (ALE) meta-analysis on 16 experiments (13 studies) examining brain activity during body odors processing. We found that the contrast EBO versus NBO resulted in significant convergence in the right middle frontal gyrus and the left cerebellum, whereas the pooled meta-analysis combining all the studies of human odors showed significant convergence in the right inferior frontal gyrus. No significant cluster was found for NBOs. However, our findings also highlight methodological heterogeneity across the existing literature. Further neuroimaging studies are needed to clarify and support the existing findings on neural correlates of processing of body odors.

Human body odor increases familiarity for faces during encoding-retrieval task.

Odors can increase memory performance when presented as context during both encoding and retrieval phases. Since information from different sensory modalities is integrated into a unified conceptual knowledge, we hypothesize that the social information from body odors and faces would be integrated during encoding. The integration of such social information would enhance retrieval more so than when the encoding occurs in the context of common odors. To examine this hypothesis and to further explore the underlying neural correlates of this behavior, we have conducted a functional magnetic resonance imaging study in which participants performed an encoding-retrieval memory task for faces during the presentation of common odor, body odor or clean air. At the behavioral level, results show that participants were less biased and faster in recognizing faces when presented in concomitance with the body odor compared to the common odor. At the neural level, the encoding of faces in the body odor condition, compared to common odor and clean air conditions, showed greater activation in areas related to associative memory (dorsolateral prefrontal cortex), odor perception and multisensory integration (orbitofrontal cortex). These results suggest that face and body odor information were integrated and as a result, participants were faster in recognizing previously presented material.

Body odors (even when masked) make you more emotional: behavioral and neural insights.

Morality evolved within specific social contexts that are argued to shape moral choices. In turn, moral choices are hypothesized to be affected by body odors as they powerfully convey socially-relevant information. We thus investigated the neural underpinnings of the possible body odors effect on the participants' decisions. In an fMRI study we presented to healthy individuals 64 moral dilemmas divided in incongruent (real) and congruent (fake) moral dilemmas, using different types of harm (intentional: instrumental dilemmas, or inadvertent: accidental dilemmas). Participants were required to choose deontological or utilitarian actions under the exposure to a neutral fragrance (masker) or body odors concealed by the same masker (masked body odor). Smelling the masked body odor while processing incongruent (not congruent) dilemmas activates the supramarginal gyrus, consistent with an increase in prosocial attitude. When processing accidental (not instrumental) dilemmas, smelling the masked body odor activates the angular gyrus, an area associated with the processing of people's presence, supporting the hypothesis that body odors enhance the saliency of the social context in moral scenarios. These results suggest that masked body odors can influence moral choices by increasing the emotional experience during the decision process, and further explain how sensory unconscious biases affect human behavior.

When to collect resting-state data: The influence of odor on post-task resting-state connectivity.

The human brain networks at rest represent spontaneous activity that is highly correlated between different brain regions. Previous studies have shown that these resting-state networks are flexible and dynamic, and they can be affected by performance of different types of tasks. Moreover, it has been suggested that the re-activation of a task-related brain network during rest promotes learning and improves the expertise on that task. However, it is still unclear whether the presence of different sensory information in the on-task state affects functional connectivity in subsequent resting-state fMRI even though the perception of the sensory information did not induce significant behavioral effects. To clarify this issue, we compared pre- and post-task resting-state fMRI of two groups of participants performing the same task either with an odor context (ODOR group) or without an odor context (AIR group). Seed-based functional connectivity analyses were performed with orbitofrontal cortex, piriform cortex and working-memory core network as seeds. The results showed that an odor context presented during an encoding task induced significant changes in the functional connectivity only within the olfactory network of the post-task resting-state compared to the same post-task situation without previous odor context. No significant difference in functional connectivity were found for the working-memory core network. This evidence emphasizes how the sensory context, in which a task is performed, is relevant for understanding the observed changes of functional connectivity during rest.

Women smelling men's masked body odors show enhanced harm aversion in moral dilemmas.

Among the most unnoticeable stimuli providing social information, body odors are powerful social tools that can modulate behavioral and neural processing. It has recently been shown that body odors can affect moral decision-making, by increasing the activations in neural areas processing social and emotional information during the decision process. The aim of the present study was twofold: 1) to test whether body odors selectively affect decisions to real dilemmatic moral scenario (incongruent) vs. fake (congruent) dilemmas, and 2) to characterize whether the impact of masked body odors is modulated by four conceptual factors: personal force, intentionality, benefit recipient and evitability. Women chose between utilitarian (sacrificing a person's life in order to save other lives) or deontological actions (deciding against the harmful action) in 64 moral dilemmas under the exposure of a neutral fragrance (masker) or a masked male body odor. Our results showed that the masked male body odor did not specifically affect the answers to real and fake dilemmas but instead, its effect is modulating whether the agent harms the victim in a direct or indirect manner (personal force) to save herself or only other people (benefit recipient). In particular, when exposed to the masked body odor participants gave more deontological answers when the harm was indirect and only other people were saved. These data support the hypothesis that body odors induce participants to perceive the individuals described in moral dilemmas as more real, triggering harm avoidance.

Influence of 4-week multi-strain probiotic administration on resting-state functional connectivity in healthy volunteers.

PURPOSE: Experimental investigations in rodents have contributed significantly to our current understanding of the potential importance of the gut microbiome and brain interactions for neurotransmitter expression, neurodevelopment, and behaviour. However, clinical evidence to support such interactions is still scarce. The present study used a double-blind, randomized, pre- and post-intervention assessment design to investigate the effects of a 4-week multi-strain probiotic administration on whole-brain functional and structural connectivity in healthy volunteers. METHODS: Forty-five healthy volunteers were recruited for this study and were divided equally into three groups (PRP: probiotic, PLP: placebo, and CON: control). All the participants underwent resting-state functional MRI and diffusion MRI brain scans twice during the course of study, at the beginning (time point 1) and after 4 weeks (time point 2). MRI data were acquired using a 3T whole-body MR system (Magnetom Skyra, Siemens, Germany). RESULTS: Functional connectivity (FC) changes were observed in the default mode network (DMN), salience network (SN), and middle and superior frontal gyrus network (MFGN) in the PRP group as compared to the PLP and CON groups. PRP group showed a significant decrease in FC in MFGN (in frontal pole and frontal medial cortex) and in DMN (in frontal lobe) as compared to CON and PLP groups, respectively. Further, significant increase in FC in SN (in cingulate gyrus and precuneus cortex) was also observed in PRP group as compared to CON group. The significance threshold was set to p < 0.05 FWE corrected. No significant structural differences were observed between the three groups. CONCLUSIONS: This work provides new insights into the role of a multi-strain probiotic administration in modulating the behaviour, which is reflected as changes in the FC in healthy volunteers. This study motivates future investigations into the role of probiotics in context of major depression and stress disorders.

Investigating Sex-Specific Characteristics of Nicotine Addiction Using Metabolic and Structural Magnetic Resonance Imaging.

Nicotine addiction is known to modulate neurotransmission and alter the brain structure. The detrimental effect of nicotine is more prominent in females as compared to males. This study sought to examine the sex-specific influence of nicotine addiction on gamma amino butyric acid (GABA) and the white matter (WM) microstructure. Sixty healthy subjects (smokers/non-smokers) underwent structural and metabolic magnetic resonance imaging scans. Results showed alterations in WM integrity (measured as changes in fractional anisotropy [FA] and GABA in smokers versus non-smokers and females versus males. No overall significant smoking and sex-specific interactions were observed in this study. However, on comparing female smokers with female non-smokers, significantly higher GABA and FA values were observed in female smokers. However, GABA and FA values did not differ significantly when male smokers were compared against male non-smokers. Our results provide a further rationale to investigate the impact of nicotine on central GABAergic function and WM integrity, in particular due to the potential risk for females to experience depressive/anxiety symptoms during smoking cessation.