Characteristics of electroencephalographic responses induced by a pleasant and an unpleasant odor

Exploring the impact of bubble type on sensory stimulation in drinks

This study explores the impact of various types of carbonation on sensory stimulation in the mouth, salivary secretion and the neurotransmitter substance P (SP), as well as body responses such as heart rate (HR) and Galvanic Skin Response (GSR). Three types of carbonation (one made using a soda machine, another carbonated with a gasifier, and the last commercial sparkling water) were used to produce different bubbles resulting in distinct sensory characteristics assessed by a trained panel. The impact of carbonation was measured by recording changes in salivary flow rate, SP levels, salivary secretory immunoglobulin A (SIgA), HR, and GSR in fifteen healthy participants. The results showed that the bubble type only affected the sensory perception of carbonation. Regardless of bubble type, carbonation increased salivary flow rate and SP values, SigA and HR. These characteristics are being sought to improve treatments for dysphagia or dry mouth. Therefore, these findings highlight the potential therapeutic application of carbonation in these situations.

Lavender Essential Oil Inhalation Improves Attentional Shifting and Accuracy: Evidence from Dynamic Changes of Cognitive Flexibility and Power Spectral Density of Electroencephalogram Signals

Background

Cognitive flexibility, a vital component of executive function, entails the utilization of extended brain networks. Olfactory stimulation has been shown to influence various brain functions, particularly cognitive performance.

Method

To investigate aroma inhalation's effects on brain activity dynamics associated with cognitive flexibility, 20 healthy adults were recruited to complete a set-shifting task during two experimental conditions: no aroma stimuli vs. lavender essential oil inhalation. Using Thomson's multitaper approach, the normalized power spectral density (NPSD) was assessed for five frequency bands.

Results

Findings confirm that aroma inhalation significantly affects behavioral indices (i.e., reaction time (RT) and response accuracy) and electroencephalogram (EEG) signatures, especially in the frontal lobe. Participants showed a tremendous increase in theta and alpha NPSD, associated with relaxation, along with beta NPSD, associated with clear and fast thinking after inhaling the aroma. NPSD of the delta band, an indicator of the unconscious mind, significantly decreased when stimulated with lavender essential oil. Further, participants exhibited shorter RT and more accurate responses following aroma inhalation.

Conclusion

Our findings revealed significant changes in oscillatory power and behavioral performance after aroma inhalation, providing neural evidence that olfactory stimulation with lavender essential oil may facilitate cognitive flexibility.

Individual Differences as a Key Factor to Uncover the Neural Underpinnings of Hedonic and Social Functions of Human Olfaction: Current Findings from PET and fMRI Studies and Future Considerations

The hedonic and social dimensions of olfactory perception are characterized by a great diversity across people. Whereas the cerebral processing underlying these aspects of odor perception have been widely explored in the last decades, very few brain imaging studies considered individual differences. This lack of consideration weakens the current models in the field, where the paradigm of universality is the norm. The present review is aimed at examining this issue. Through a synthetic summary, we will first present past studies suggesting that (1) hedonics are represented consistently throughout the olfactory system from primary to secondary areas, with a progressive cognitive modulation and integration with other senses, (2) social dimension of odors may be represented in a distinct pathway involving social and attentional networks. In a second, and more critical part, we will highlight the importance of individual differences for the cerebral study of human olfaction.

Chemosensory Perception: A Review on Electrophysiological Methods in “Cognitive Neuro-Olfactometry”

Various brain imaging techniques are available, but few are specifically designed to visualize chemical sensory and, in particular, olfactory processing. This review describes the results of quantitative and qualitative studies that have used electroencephalography (EEG) and magneto-encephalography (MEG) to evaluate responses to olfactory stimulation (OS). EEG and MEG are able to detect the components of chemosensory event-related potentials (CSERPs) and the cortical rhythms associated with different types of OS. Olfactory studies are filling the gaps in both the developmental field of the life cycle (from newborns to geriatric age) and the clinical and basic research fields, in a way that can be considered the modern “cognitive neuro-olfactometry”.

Evaluation of human electroencephalogram change for sensory effects of fragrance

BACKGROUND

The stabilizing effect of lavender and the arousal effect of peppermint essential oils are acknowledged and used widely in aromatherapy and the cosmetics industry. However, no evaluation method confirms the effects of essential oils through quantitative and objective electroencephalogram (EEG) results; instead, only a psychological and subjective method exists. Therefore, this study aims to create a new emotional cosmetic evaluation paradigm using EEG values. Moreover, it enables quantitative interpretation of the results in addition to the subjective survey outcomes.

METHODS

For this study, 12 healthy female Korean participants were recruited and three fragrances were used. The EEG results were collected for 3 minutes (1 minute each before, during, and after inhalation of every fragrance).

RESULTS

The quantitative EEG outcomes indicate changes in the participant's brainwaves before and after inhalation. Significant changes in the EEG were observed. Based on the results, the effects of fragrances were confirmed to be stabilizing for lavender, and arousing for peppermint and coffee aroma. Furthermore, the subjective questionnaire results indicate similar tendency as that of the quantitative EEG results.

CONCLUSION

In addition to psychological and subjective assessments, our emotional evaluation method can verify the cosmetic fragrance effects through quantitative and objective results.

The effect of odor valence on olfactory performance in schizophrenia patients, unaffected relatives and at-risk youth

Given the presence of odor identification impairment in individuals with schizophrenia and recent evidence of aberrant odor hedonic processing, the aim of this investigation was to examine the influence of valence and intensity on odor identification in schizophrenia patients, their first-degree family members, and young persons at clinical risk for psychosis. Participants completed the 16-item Sniffin' Stick Odor Identification Test. A logistic regression was conducted to assess the influence of valence and intensity on odor identification accuracy. Identification performance in the schizophrenia patients and youths at clinical risk for psychosis was significantly influenced by odor valence, but not intensity. Identification accuracy in first-degree family members was not influenced by valence or intensity. These data suggest that abnormalities in odor valence perception may represent an environmentally-mediated marker for hedonic disturbance that could have predictive utility in future conversion to psychosis. Further research examining the utility of odor valence measures as markers for psychosis risk is warranted.

Odor hedonic capacity and anhedonia in schizophrenia and unaffected first-degree relatives of schizophrenia patients

OBJECTIVE

There is increasing evidence that schizophrenia patients have difficulties in the hedonic appraisal of odors. In a prior study, we assessed olfactory hedonic perception birhinally and found that males with schizophrenia failed to attach the appropriate hedonic valence to a pleasant odor, despite correctly perceiving changes in odor intensity. Female patients, in contrast, exhibited normal responses. The current study extends this work by examining odor valence processing in unaffected first-degree relatives of schizophrenia patients, to determine the extent to which this abnormality may be genetically mediated. We also examine odor valence processing unirhinally, rather than birhinally, to probe possible lateralized differences in patients' hedonic processing deficits.

METHOD

Individuals with schizophrenia (n = 54), first-degree unaffected family members (n = 22), and demographically matched controls (n = 45) were administered the Suprathreshold Amyl Acetate Odor Intensity and Odor Pleasantness Rating Test.

RESULTS

In contrast to family members and controls, both male and female schizophrenia probands underevaluated the hedonic characteristics of amyl acetate at lower concentrations and overevaluated its pleasantness at concentrations perceived as unpleasant by both controls and relatives. These patient-specific differences could not be explained by differences in smoking habit, medication use, or subjective ratings of odor intensity. However, they were associated with increased levels of anhedonia/asociality and negative symptomatology.

CONCLUSIONS

Our findings suggest that both male and female schizophrenia patients have difficulties in the unirhinal appraisal of hedonic valence. Normal responses in unaffected first-degree relatives suggest that this is an environmentally, rather than genetically, mediated abnormality denoting negative symptomatology.

Non-linear quantitative electroencephalographic (qEEG) changes during processing of chemo-sensory stimulations: a preliminary study

The present study was to investigate the processing of pleasant smell and taste stimuli by non-linear EEG measures. Point correlation dimension (PD2i) has been used for studying the local, and synchronization likelihood (SL) the global dynamical organization. Nine healthy subjects participated in this study. After a baseline period of 30s the patients were given a perfume cap or a chocolate taste for 30s. The analysis was performed off-line on 16 channels. After smell stimulation an immediate bilateral but short response was seen. First a decrease and afterwards an increase were found in the mean PD2i. In contrast, the taste stimulation resulted in a later reaction mainly on the right side. The SL in the slow alpha band decreased during the first 15s after both stimulations. In the second 15s, however, a remarkable SL increase was seen mainly in the 7-14Hz and in every frequency band. The decreased mean PD2i and SL values could be interpreted by the simplified network preparation to cognitive data processing. The PD2i and SL methods detected subtle dynamical changes during olfactory and gustatory processes suitable for collection normative database to pathological conditions.

Unpleasantness and physiological responses in using sanitary napkins

This study investigated the physiological and psychological effects of sanitary napkins (SN) on women in hemorrhage treatment during the menstrual phase. Mesh and non-woven napkins were employed, and the effects were studied during the follicular and menstrual phases; mesh SN presented a higher textural surface-roughness. In both phases, the increases in systolic and diastolic blood pressure were significantly dependent on the application intervals. The low-frequency component of systolic blood pressure variability significantly increased, while the salivary secretion rate decreased with the use of mesh SN during the follicular phase compared with non-woven SN. In addition, the heart rate during the menstrual phase significantly increased in subjects after the replacement of mesh SN compared with non-woven SN. In cases of wearing the unpleasant mesh SN, electroencephalography (EEG) manifested bilateral enhancements in beta and alpha2 waves in the frontal areas increased arousal level during both phases. From the above findings, napkin use increased physiological loading and wearing napkins with higher textural surface-roughness tended to increase activities of the autonomic nervous system and brain arousal level.

Physiological Responses Induced by Pleasant Stimuli

The specific physiological responses induced by pleasant stimuli were investigated in this study. Various physiological responses of the brain (encephaloelectrogram; EEG), autonomic nervous system (ANS), immune system and endocrine system were monitored when pleasant stimuli such as odors, emotional pictures and rakugo, a typical Japanese comical story-telling, were presented to subjects. The results revealed that (i) EEG activities of the left frontal brain region were enhanced by a pleasant odor; (ii) emotional pictures related to primitive element such as nudes and erotic couples elevated vasomotor sympathetic nervous activity; and (iii) an increase in secretory immunoglobulin A (s-IgA) and a decrease in salivary cortisol (s-cortisol) were induced by rakugo-derived linguistic pleasant emotion. Pleasant emotion is complicated state. However, by considering the evolutionary history of human being, it is possible to assess and evaluate pleasant emotion from certain physiological responses by appropriately summating various physiological parameters.

Electroencephalographic responses and subjective evaluation on unpleasantness induced by sanitary napkins

Correlation of unpleasantness and electroencephalography (EEG)-based responses induced by persistent mechanical/dry stimulation and acute wet stimulation via wearing sanitary napkins (SN) was investigated in the present study. Mesh and nonwoven SN were employed, and the effects were studied during the follicular and menstrual phases. The mesh SN characteristically displayed a higher textural surface-roughness. The results in the follicular phase revealed no change in EEG responses to nonwoven SN-induced persistent mechanical stimulation, while the same dry stimulus induced significant increases in alpha2 and beta activities in the bilateral frontal areas accompanied by markedly exacerbated unpleasantness with mesh compared with nonwoven SN. The present result with SN application confirms the previous finding that unpleasantness is well correlated with EEG responses of bilateral frontal areas. Interestingly, although the alpha2 activities were enhanced more with mesh than nonwoven SN during the menstrual phase, unpleasantness between the two textural materials was not different. Moreover, it is suggested that acute unpleasantness induced by wet stimulation is related with elevated EEG responses in the left hemisphere. These data suggest that subjective evaluation of effects of physical stimulation on the human body may not be adequately reliable, and objective assessment of physiological activities with EEG is warranted.