Is odor processing related to oral breathing?

Acute particulate matter exposure diminishes executive cognitive functioning after four hours regardless of inhalation pathway

Recent evidence suggests short-term exposure to particulate matter (PM) air pollution can impact brain function after a delay period. It is unknown whether effects are predominantly due to the olfactory or lung-brain pathways. In this study 26 adults (Mage = 27.7, SDage = 10.6) participated in four conditions. They were exposed to either high PM concentrations or clean air for one hour, using normal inhalation or restricted nasal inhalation and olfaction with a nose clip. Participants completed four cognitive tests before and four hours after exposure, assessing working memory, selective attention, emotion expression discrimination, and psychomotor vigilance. Results showed significant reductions in selective attention and emotion expression discrimination after enhanced PM versus clean air exposure. Air quality did not significantly impact psychomotor vigilance or working memory performance. Inhalation method did not significantly mediate effects, suggesting that short-term PM pollution affects cognitive function through lung-brain mechanisms, either directly or indirectly.

You See What You Smell: Preferential Processing of Chemosensory Satiety Cues and Its Impact on Body Shape Perception

The current study examines neural responses to satiety- and fasting-related volatiles and their effect on the processing of body shapes. Axillary sweat was sampled with cotton pads from 10 individuals after 12 h of fasting, and after having consumed a standard breakfast. Pure cotton pads served as the control. The chemosensory stimuli were presented to 20 participants (via a constant-flow olfactometer) exclusively, and additionally as context to images of overweight and underweight avatars. EEG was recorded (61 electrodes), and chemosensory (CSERPs; P1, N1, P2, P3) and visual event-related potentials (VERPs; N1, P2, P3a, P3b) were analyzed. The amplitudes of all positive CSERP components differed more strongly from cotton in response to chemosensory satiety cues as compared to fasting cues (P1: p = 0.023, P2: p = 0.083, P3: p = 0.031), paralleled by activity within the middle frontal and temporal gyrus. Overweight compared to underweight body shapes tended to elicit larger VERP P2 amplitudes (p = 0.068), and chemosensory satiety cues amplified the VERP amplitudes in response to any body shape (P2, P3a, P3b; all p_s ≤ 0.017) as compared to the cotton control. The results indicate that chemosensory satiety cues transmit complex social information, overriding the processing of analogous visual input.

Chemosensory communication of aggression: women's fine-tuned neural processing of male aggression signals

The current study is the first to examine the central nervous processing of aggression chemosignals within men and women by means of chemosensory event-related potential (CSERP) analysis. Axillary sweat was collected from 17 men and 17 women participating in a competitive computer game (aggression condition) and playing a construction game (control condition). Sweat samples were pooled with reference to donor gender and condition, and presented to 23 men and 25 women via a constant flow olfactometer. Ongoing electroencephalogram was recorded from 61 scalp locations, CSERPs (P2, P3-1, P3-2) were analysed and neuronal sources calculated (low-resolution electromagnetic tomography, LORETA). Women, especially, showed larger P3-1 and P3-2 amplitudes in response to male as compared with female aggression signals (all p values < 0.01). The peak activation of this effect was related to activity within the dorsomedial prefrontal cortex (Brodmann area 8). As male aggression commonly targets physical harm, the competence of the human brain to sensitively detect male aggression signals is considered to be highly adaptive. The detection of male aggression signals seems to be of higher importance for women than for men. It is suggested that the processing of male aggression signals in women induces an immediate response selection. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Oral health status of children with mouth breathing due to adenotonsillar hypertrophy

OBJECTIVES

Mouth breathing is an important health problem, commonly encountered in children. In children, adeno-tonsillar hypertrophy is the main reason causing partial or complete upper airway obstruction and reduction in airflow. This study aimed to determine the oral health status of children aged 3-15 years, with mouth breathing who were due to have surgery for adeno-tonsillar hypertrophy and referred to the Department of Otorhinolaryngology at Children's Hospital of a University in Ankara, Turkey between January-July 2015.

METHODS

The approval of the Non-Interventional Clinical Researches Ethics Board of Hacettepe University and written informed consents from the parents were obtained. The parents completed a questionnaire before the surgery. The children were examined using dental mirror and explorer under dental unit lighting. Oral health status was evaluated with DMFT/S, dmft/s, ICDAS II, dental plaque and gingival indices. The chi-square test, Kruskal Wallis and Mann Whitney U tests were used to statistically analyse the results, with statistical significance p<0.05.

RESULTS

Of the 170 children who had adenotonsillar hypertrophy with mouth breathing, 150 the parents agreed to participate the study. 77 of the children (51.3%) were male; the mean age was 5.9 ± 2.6. Mean dmft was 3.8 ± 3.6, dmfs 9.7 ± 1.1, DMFT 0.4 ± 1.0 and DMFS 0.6 ± 1.5 respectively. Among the children, 101 (67.3%) had cavitated dental caries, and according to ICDAS II, none had healthy teeth, 15 (10.0%) had initial, 42 (28.0%) had moderate and 93 (62.0%) had advanced caries. Of the children, 89.3% had gingivitis and the proportion of gingivitis in posterior region was found to be significantly higher than anterior region (p < 0,001).

CONCLUSIONS

The oral health status of mouth breathing in children with adeno-tonsillar hypertrophy was poor. To reduce the risk of dental caries and periodontal disease among these children, regular dental follow-up and preventive programmes for oral health are needed.

Pregnancy reduces the perception of anxiety

In humans, stress can be contagiously transmitted via chemosignals on a subconscious level. This study investigates how pregnancy affects neural responses to anxiety chemosignals. Using cotton pads, 28 men donated axillary sweat immediately before an academic examination (anxiety sweat) and during ergometer training (control). Via a constant-flow olfactometer, samples were presented (oddball paradigm) to 12 non-pregnant (NP) women, 14 women in their first (T1), and 18 in their third (T3) trimester of pregnancy. Chemosensory event-related potentials and current source densities (CSD) were analysed (60 electrode setup). Compared to NP-women, pregnant women display diminished evaluative processing of the sweat samples (targets; P3-1/ P3-2 amplitudes) and delayed evaluative processing of the anxiety sweat (targets; P3-2 latency). T3-women show attenuated early processing (targets; N1 amplitude) compared to NP-women, and reduced evaluative processing compared to T1-women (standards; P3-2 amplitude). CSDs (P3-1/ P3-2 latency ranges) reveal that T1- and T3-women show an atypical activation distribution to anxiety sweat. Most participants were unable to detect the sweat samples (anxiety sweat: 79.5%, sport sweat 88.6%). The results demonstrate that the processing of anxiety chemosignals progressively vanishes during pregnancy. This effect is likely to occur without any cognitive control.

Human amygdala activations during nasal chemoreception

This review serves as a comprehensive discussion of chemosensory stimulation of the amygdala in healthy humans. Following an introduction of the neuroanatomy of chemosensory processing in primary and secondary olfactory structures, functional resonance magnetic imaging and positron imaging tomography studies are systematically categorized based on valence of stimuli, stimulus concentration, and paradigm-dependent amygdala activation. The amygdala shows patterns of lateralization due to stimulus valence. Main findings include pleasant odors being associated with bilateral or left amygdala activation, and unpleasant odors being associated with activation of the right amygdala, suggesting a crucial role of the right amygdala in evolutionary preservation. Potentially threatening social stimuli, however, might be processed apart from the olfactory system and tend to activate the left amygdala. Amygdala response to chemosensory stimuli correlated with simultaneous activation in the orbitofrontal cortex (OFC), piriform cortex (PC), and insula, suggesting a close-knit network of these areas during stimulus processing.

Neuronal generator patterns of olfactory event-related brain potentials in schizophrenia

To better characterize neurophysiologic processes underlying olfactory dysfunction in schizophrenia, nose-referenced 30-channel electroencephalogram was recorded from 32 patients and 35 healthy adults (18 and 18 male) during detection of hydrogen sulfide (constant-flow olfactometer, 200 ms unirhinal exposure). Event-related potentials (ERPs) were transformed to reference-free current source density (CSD) waveforms and analyzed by unrestricted Varimax-PCA. Participants indicated when they perceived a high (10 ppm) or low (50% dilution) odor concentration. Patients and controls did not differ in detection of high (23% misses) and low (43%) intensities and also had similar olfactory ERP waveforms. CSDs showed a greater bilateral frontotemporal N1 sink (305 ms) and mid-parietal P2 source (630 ms) for high than low intensities. N1 sink and P2 source were markedly reduced in patients for high intensity stimuli, providing further neurophysiological evidence of olfactory dysfunction in schizophrenia.

Intensified neuronal investment in the processing of chemosensory anxiety signals in non-socially anxious and socially anxious individuals

Background

The ability to communicate anxiety through chemosensory signals has been documented in humans by behavioral, perceptual and brain imaging studies. Here, we investigate in a time-sensitive manner how chemosensory anxiety signals, donated by humans awaiting an academic examination, are processed by the human brain, by analyzing chemosensory event-related potentials (CSERPs, 64-channel recording with current source density analysis).

Methodology/Principal Findings

In the first study cerebral stimulus processing was recorded from 28 non-socially anxious participants and in the second study from 16 socially anxious individuals. Each individual participated in two sessions, smelling sweat samples donated from either female or male donors (88 sessions; balanced session order). Most of the participants of both studies were unable to detect the stimuli olfactorily. In non-socially anxious females, CSERPs demonstrate an increased magnitude of the P3 component in response to chemosensory anxiety signals. The source of this P3 activity was allocated to medial frontal brain areas. In socially anxious females chemosensory anxiety signals require more neuronal resources during early pre-attentive stimulus processing (N1). The neocortical sources of this activity were located within medial and lateral frontal brain areas. In general, the event-related neuronal brain activity in males was much weaker than in females. However, socially anxious males processed chemosensory anxiety signals earlier (N1 latency) than the control stimuli collected during an ergometer training.

Conclusions/Significance

It is concluded that the processing of chemosensory anxiety signals requires enhanced neuronal energy. Socially anxious individuals show an early processing bias towards social fear signals, resulting in a repression of late attentional stimulus processing.

Increased processing speed for emotionally negative odors in schizophrenia

Although olfactory identification deficits in schizophrenia have been repeatedly demonstrated, some studies indicate that schizophrenia patients may also show an olfactory hypersensitivity. In addition, recent evidence points to impaired odor hedonics in schizophrenia. It was the aim of the present study to investigate olfactory information processing in schizophrenia patients with positive symptoms, by means of chemosensory event-related potential (CSERP) analysis. To control for modality-specific effects, these data were compared to visual event-related potentials (VERP), and in order to control for disorder-specific effects, the schizophrenia patients were compared to healthy controls as well as to patients with major depressive disorder (MDD). In each group, nine subjects were investigated. During EEG recording (32 scalp locations) two odors (positive valence: phenyl-ethylalcohol, negative valence: isobutyraldehyde) were presented using the constant flow method. Afterwards, two colors (red, yellow) were presented. The schizophrenia patients responded to both odors with shorter CSERP latencies than healthy controls and MDD-patients. This effect was most pronounced for the early processing (N1 component) of the emotionally negative odor. However, in response to colors, schizophrenia patients showed increased N1 latencies and a reduced P3 amplitude. It will be discussed whether schizophrenia patients with positive symptoms show a general processing advantage for emotionally negative (threat-related) information.

Central odor processing in subjects experiencing helplessness

The aim of the present study was to investigate whether central nervous odor processing is affected by the temporary experience of helplessness. To induce helplessness, an unsolvable social discrimination test in combination with false feedback was used. The EEG was recorded from 60 scalp locations, while two standard odors were presented via a constant-flow olfactometer. Helplessness attenuated olfactory stimulus processing at an early perceptual stage: the P2 and P3-1 amplitudes were reduced in response to both odors. Furthermore, the early potentials (N1, P2 and P3-1) of the chemosensory event-related potential (CSERP) appeared with longer latencies when subjects received negative feedback. The state effects of helplessness resemble the deviations in the CSERP found in depressed patients, suggesting a general mood effect.

The human brain is a detector of chemosensorily transmitted HLA-class I-similarity in same- and opposite-sex relations

Studies on subjective body odour ratings suggest that humans exhibit preferences for human leucocyte antigen (HLA)-dissimilar persons. However, with regard to the extreme polymorphism of the HLA gene loci, the behavioural impact of the proposed HLA-related attracting signals seems to be minimal. Furthermore, the role of HLA-related chemosignals in same- and opposite-sex relations in humans has not been specified so far. Here, we investigate subjective preferences and brain evoked responses to body odours in males and females as a function of HLA similarity between odour donor and smeller. We show that pre-attentive processing of body odours of HLA-similar donors is faster and that late evaluative processing of these chemosignals activates more neuronal resources than the processing of body odours of HLA-dissimilar donors. In same-sex smelling conditions, HLA-associated brain responses show a different local distribution in male (frontal) and female subjects (parietal). The electrophysiological results are supported by significant correlations between the odour ratings and the amplitudes of the brain potentials. We conclude that odours of HLA-similar persons function as important social warning signals in inter- and intrasexual human relations. Such HLA-related chemosignals may contribute to female and male mate choice as well as to male competitive behaviour.

Assessment of olfactory and trigeminal function using chemosensory event-related potentials

GOALS

To give an overview on the theoretical and practical applications of chemosensory event-related potentials.

METHODS

Chemosensory event-related potentials (ERPs) may be elicited by brief and precisely defined odorous stimuli. Based on the principles of air-dilution olfactometry, a stimulator was developed in the late 1970s, which allows stimulation of the olfactory neuroepithelium and the nasal mucosa with no concomitant mechanical stimulation. Chemosensory ERPs were obtained after stimulation of the olfactory nerve (olfactory ERPs) or the trigeminal nerve (somatosensory or trigeminal ERPs). The characteristics of the stimulator for chemosensory research as well as the variables influencing the responses are discussed in this paper.

RESULTS

Implementation and normative data from our department are reported with different clinical examples from otorhinolaryngologic clinic. The bulk of the evoked response consists of a large negative component (often referred to as N1), which occurs between 320 and 450 ms after stimulus onset. This component is followed by a large positive component, often referred to as P2, occurring between 530 and 800 ms after stimulus onset. Absence of olfactory ERPs and presence (even with subtle changes) of somatosensory ERPs is a strong indicator of the presence of an olfactory dysfunction.

CONCLUSIONS

This review examines and discusses the methods of chemosensory stimulation as well as the electrophysiological correlates elicited by such stimuli. The clinical applications of chemosensory ERPs in neurology and otorhinolaryngology are outlined.

Convergent and divergent effects of odors and emotions in depression

The aim of the present study was to investigate the similarities and differences in the olfactory and visual processing of emotional stimuli in healthy subjects and in patients with major depressive disorder (MDD). Twenty-five inpatients were investigated after admission to the psychiatric clinic. Fifteen of them participated a second time, shortly before their discharge from the hospital. A group of healthy subjects, matched according to age and sex, served as a control. Chemsosensory event-related potentials (CSERPs) were recorded using the constant flow method. In addition, event-related potentials (ERPs), in response to colors and emotional slides, were obtained to control modality and emotion-specific effects. The subjects' task was to discriminate the colors (red/yellow) and odors (phenyl-ethylalcohol = rose/ isobutyraldehyde = rotten butter) according to their quality and to judge the valence of the emotional slides (IAPS slides). The EEG was recorded from 32 scalp locations. At the beginning of the therapy, visual stimulus processing was attenuated in depressive subjects at a relatively late processing level (reduced amplitudes of the P3 and pSW in response to colors and emotional slides), whereas olfactory stimulus processing had already been affected at an early level (reduced amplitudes of the P2 and P3-1 peaks in MDD patients). However, after successful medical treatment, ERPs did not differentiate between depressive patients and healthy controls. We discuss whether functional deviations within the primary olfactory cortex are responsible for the lower olfactory sensitivity, as well as for the altered emotional stimulus processing in MDD patients.

Development of a continuous respiration olfactometer for odorant delivery synchronous with natural respiration during recordings of brain electrical activity

The continuous respiration olfactometer (CRO) was designed as a respiration-synchronous method for delivering odorants during recordings of brain electrical activity, providing control and monitoring of the timing of the delivery as well as the quantities of odorant involved. The CRO incorporates a purpose-built electronic system designed with very specific temporal and quantitative characteristics, and is composed of four main parts: the respiratory monitoring apparatus, the odorant/air delivery system, the serial interface device and the respiratory monitoring software. Tests were undertaken to determine the performance of the system with reference to the accuracy and precision of timing and control of odorant delivery. Tests were also undertaken to determine the effects of variations in natural respiration between subjects on the capability of the respiratory monitoring system, using a group of 50 subjects, to test the success of a variable gain control to optimize the range of the digitized respiratory output. The delivery system was able to provide information concerning quantities of air or odorant delivered, and the stimulus timing information required for integration with neurophysiological recording techniques.

Olfactory event-related potentials in patients with brain tumors

OBJECTIVE

The aim of the study was to determine how odor processing is altered in patients with unilateral supratentorial brain tumors.

METHODS

Olfactory event-related potentials (OERPs) were evaluated in 10 patients with unilateral brain tumors of the frontal or temporal lobe in response to linalool and allylcaproate. Both odors were presented monorhinally by a constant-flow olfactometer. In addition, 20 healthy subjects were examined. While sniffing, the subjects were asked to discriminate the two odors. EEG was recorded from 7 electrode positions (Fz, Cz, Pz, F3/4, P3/4). Amplitudes and latencies of 3 peaks (N1, P2, P3) were measured. To control for effects of modality-non-specific alterations on the olfactory components acoustic event-related potentials (AERPs) were registered by use of an oddball paradigm.

RESULTS

Patients with right-sided lesions showed distinct deficits in the discrimination task after stimulation of the right and left nostril. In contrast, patients with left-sided lesions only had an attenuation of correct reactions after left-sided stimulation. In the OERPs, patients with right-sided lesions showed P2- and P3-components with decreased amplitudes at parietal electrode positions. These alterations appeared after ipsi- and contralateral stimulation. Patients with left-sided lesions showed a significant effect of the side of stimulation. Their OERP-amplitudes were decreased after left-sided stimulation but not after right-sided stimulation. After right-sided olfactory stimulation a correlation between the olfactory and the acoustic ERP was seen in patients with right-sided lesions.

CONCLUSIONS

Olfactory performance of the participating patients was markedly reduced. Patients with right-sided lesions showed bilateral impairment, which would support the importance of the right hemisphere in olfaction. The alteration of the topographic distribution of P2- and P3-amplitudes in patients with right-sided lesions might reflect an impairment of early and late olfactory processing steps.

Odorants elicit evoked potentials in the human amygdala

Electroencephalographical (EEG) recording studies have shown that odorants produce olfactory evoked potentials (OEPs) on the scalp surface. However, EEGs can only provide limited information about the intracerebral sources from where the OEPs are generated. By contrast, intracerebral EEG recordings enable direct examination of the electrophysiological activity from a given cerebral area. In the present study, neural activity was recorded from the amygdala of seven epileptic patients undergoing intracerebral EEG recordings prior to surgical treatment for relief of intractable seizures. Two olfactory tests were used: a passive-stimulation test consisting of the successive presentation of 12 common odorants and a suprathreshold detection test including both odorant and non-odorant stimulations. Recordings from the amygdala revealed that all odorant stimulations induced large and reproducible OEPs, whereas the non-odorant stimulations did not. It was also found that repetition of the same odorant stimulation led to a decrease in the latency of the first OEP component. This modulation, which corresponds to a faster olfactory processing, strongly suggests that the amygdala is involved in early olfactory attentional processes. In conclusion, it appears that the human amygdala discriminates the incoming information from the nasal airflow as being odorant or not and, additionally, that its speed of processing is sensitive to recent experience with an odor.

Age-related changes in olfactory processing detected with olfactory event-related brain potentials using velopharyngeal closure and natural breathing

Previous olfactory event-related potential (OERP) studies often employed the Velopharyngeal Closure (VC) method, which prevents respiratory air flow in the nose during odor presentation. However, the use of VC has limited the application of OERPs to populations able to perform this artificial breathing technique. The present study investigated the effects of Natural Breathing (NB) in comparison to VC on OERP latency and amplitude in young (mean age: 24 years) and elderly (mean age: 71 years) adults. OERPs were recorded from three midline scalp electrodes (Fz, Cz, Pz) for 15 trials in each breathing condition with an interstimulus interval of 3.5 min, using amyl-acetate as stimulus. Subjects were asked to report perceived stimulus intensity. A thermistor placed inside one nostril monitored nasal respiration and performance of VC. In the NB condition, subjects were instructed to breathe normally through mouth and nose, while stimulus presentation occurred during inspiration. In both breathing conditions, elderly subjects showed significantly smaller N1-P2 and N1-P3 interpeak amplitudes and longer latencies for N1, P2, P3 than younger subjects. VC generated significantly larger N1-P2 amplitudes across all electrode sites, whereas Natural Breathing produced a trend towards shorter P3 latencies. No significant interaction was found between age and breathing technique. The present investigation showed that the OERP is a sensitive measure for detecting age-related changes in olfactory function regardless of breathing technique.

Complexity of olfactory lateralization processes revealed by functional imaging: a review

Currently available techniques used in neurosciences and particularly cerebral imaging are contributing to a better understanding of human perception and the treatment of sensorial information. In this field, the chemical senses (taste and smell) have received little attention when compared with the auditory, visual and tactile senses. Nevertheless, recent research has been trying to overcome this. Brain regions involved in the processing of olfactory information have been investigated in several studies including a large number dealing with the question of lateralization. However, functional asymmetry in olfaction has still not been resolved and the resulting data have not been homogeneous. In this field, the contribution of cerebral imaging studies is very important insofar as it shows that the processes of functional lateralization in olfaction depend on many factors (nature of stimulus, nature of task, characteristics of subjects ...) that future research will have to consider.

Chemosensory event-related potentials (CSERP) as a key to the psychology of odors

The present article gives a critical overview of how the components N1, N2, especially the mismatch negativity (MMN), and P3 have been investigated and interpreted in the context of 'chemosensory event-related potential' (CSERP) research. In order to integrate the respective CSERP results, findings and theoretical models from other modalities are briefly described for each component. It is suggested that all components found so far within the CSERP strongly depend on the psychological state of the individual. In particular the dominant positivity of the CSERP has been focused on by investigating the specificity of olfactory emotional processing in comparison to emotional and neutral stimuli from the visual modality. The results reveal that the late positive complex within the CSERP consists of two subcomponents, one of which has a frontal and the other a parietal dominance. The posterior positivity seems to reflect the features of the P3 component and varies with the valence of odors, whereas the anterior positivity seems to be similar to the Novelty-P3. A link between olfactory and emotional processing has been confirmed by the finding that the P3 elicited by visual stimuli shows similar valence effects.

The application of electroencephalographic techniques to the study of human olfaction: a review and tutorial

The use of a variety of electrophysiological techniques to determine the effects of odor on the nervous system is reviewed. Methods and problems associated with the collection of on-going EEG, chemosensory event-related potentials, and contingent negative variation data are discussed in depth as is the use of odors as modulators of brain potentials produced by other senses. In addition, the advantages of several seldom used EEG analysis techniques are discussed with respect to the unique problems of understanding olfaction.