Chemosensory Event-related Potentials Research Articles

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.

Sensitivity to androstenone in female subjects is associated with an altered brain response to male body odor

Androstenone is a boar pheromone, and has also been found within different human body fluids. However, it is still unclear whether it carries pheromonal information in humans and whether it contributes significantly to the complex human body odor at all. Some humans fail to perceive the odor of androstenone, but most of these anosmics can achieve sensitivity by daily sniffing. The following study was designed to investigate whether sensitivity to androstenone influences the perception of body odors. Four females osmic to and four females anosmic to androstenone attended two EEG sessions. Anosmics were successfully sensitized to androstenone between sessions. CSERPs (chemosensory event-related potentials) were obtained while subjects perceived their own body odor and a male body odor within an olfactory oddball paradigm. The CSERPs showed a general decrease in amplitude from the first to the second session except for the sensitized anosmics in response to male body odor. The results indicate that the sensitivity to androstenone in females is associated with a stronger brain response to male body odor.

Is odor processing related to oral breathing?

This paper addresses two questions related to the inherent association between breathing and odor perception: Does central nervous processing of odors change when an artificial breathing technique (velopharyngeal closure) is introduced and secondly, does odor processing vary with the oral breathing phase (inhalation or exhalation)? Chemosensory event-related potentials (CSERP) were obtained from eight female subjects while they were smelling an odor mixture (citral, eugenol, linalool, menthol and isoamylacetate). Each subject was required to perform spontaneous mouth breathing (120 trials) as well as the velopharyngeal closure technique (120 trials). Simultaneously, a thermistor monitored the phase of the respiratory cycle. The results reveal that the central nervous correlates of odor processing change with the breathing technique but not with the oral breathing cycle. The findings that early stimulus processing is faster (N1 latency) and late stimulus processing more pronounced (P3 amplitudes) when the subjects are breathing spontaneously are discussed with regard to attentional effects. The reduction of the N1 amplitude during the spontaneous breathing condition may be caused by larger latency variations and longer stimulus rise-times. Furthermore, it is concluded that the oral breathing cycle is less important than the nasal breathing cycle for olfactory information transmission.

Chemosensory event-related potentials to trigeminal stimuli change in relation to the interval between repetitive stimulation of the nasal mucosa.

Event-related potentials (ERPs) to olfactory and trigeminal stimuli have been used commonly to evaluate chemosensory dysfunction. The aim of the present study was to investigate how ERPs could be modified by repetitive stimulations of the intranasal trigeminal nerve using 52% v/v CO2 stimuli for 200 ms periods. Nine subjects were exposed to 6 sessions each during which trains of 16 stimuli were applied. The interval between stimuli was constant for each experiment, but varied between experiments (10, 20, 30, 40, 60, and 90 s). Trigeminal ERPs were obtained from three positions on the skull. Both intensity ratings and ERP amplitudes decreased as the interstimulus interval (ISI) shortened. Specifically, ratings and response amplitudes were most strongly reduced by approximately 30-50% at the shortest ISI used (10 s) and were largest at an ISI of 90 s. The decrease of amplitudes was strongest for the P46 amplitude. Our findings suggest that this may be the result of both habituation and stimulus predictability. We hypothesize that the ISI dependence of chemosensory ERPs may also be a function of an interaction between Adelta and C fibers.

Central nervous correlates of chemical communication in humans.

The recording of chemosensory event-related potentials (CSERPs) has been established as an objective method in the assessment of central odor processing in humans. In the present study CSERPs were used to investigate whether human body odor is genetically determined by the major histocompatibility complex (MHC), referred to in humans as the human leukocyte antigen (HLA). The immunological function of the MHC is the discrimination of self/nonself within the immune system. In rodents it has been shown that body odor is significantly influenced by the MHC and that it can be discriminated by members of different species. To create a sufficiently large subject pool, 144 subjects were screened for their HLA class I loci A and B. During the electroencephalography (EEG) session the subjects (n = 40/20 women) were confronted with the body odor (axillary hair) of three different donors. Two donors (d1 and d2) were HLA-similar but had a different HLA type than the third donor (d3) and the perceiving subject. The third donor and the perceiver shared a similar HLA type. Half of the perceivers received odors from donors of the same sex, the other half smelt odors from donors of the opposite sex. In the EEG session subjects were presented with 200 trials. The odors were delivered through a constant flow olfactometer non-synchronously to breathing. The odor of d1 appeared frequently (p = 0.6) whereas the odors of d2 and d3 appeared each at a rate of p = 0.2. During half the trials the subjects were instructed to respond to the odor of d2, during the other half to the odor of d3. The EEG was recorded from Fz, Cz, Pz, F3, P3, F4 and P4 in reference to linked mastoids. First results show that male perceivers show enhanced potentials in response to male donors of a similar HLA type (d3). The CSERP results of the other groups as well as valence and attractiveness ratings will be discussed.

Attentional modulation of central odor processing.

Two studies were conducted to investigate the influence of attention on the components of the chemosensory event-related potential (CSERP). In the first study the odors linalool and eugenol were delivered to six male subjects, in the second study three male and two female subjects were presented with their own body odor (axillary hair) and the body odor of a same sex donor. In both studies the odors were presented in an oddball paradigm under ignore and attend conditions via a constant-flow olfactometer. In the ignore condition attention was diverted from the odors with a distractor task, while in the attend condition the subjects were asked to respond to the infrequently occurring odor. In both studies the allocation of attention led to a decrease in the latency of the early components (N1, P2, N2) and to an increase in the amplitude of the late positivities. The modulation of the early components suggests that attentional gating in olfaction might already be effective at an early processing level.

Olfactory and intranasal trigeminal event-related potentials in anosmic patients.

The aim of this study was to investigate the usefulness of chemosensory event-related potentials (CSERPs) in response to both olfactory and intranasal trigeminal stimulation in the diagnosis of anosmia. Forty-four patients participated. Gaseous CO2 was used for trigeminal stimulation, vanillin and H2S were used as olfactory stimulants. Event-related potentials to olfactory stimuli could not be obtained in any of the anosmic patients, indicating the complete loss of the sense of smell. However, all patients responded to stimulation of the trigeminal nerve with CO2. These data clearly demonstrate the clinical significance of CSERPs in the assessment of anosmia.

Chemosensory event-related potentials change with age

The study examined age-related changes in the perception of olfactory and trigeminal chemical stimuli using chemosensory event-related potentials (CSERP). Three groups of healthy volunteers, each comprised of 8 men and 8 women, were tested (age ranges 15–34, 35–54, and 55–74 years). Subjects underwent extensive psychological testing focusing on impairments of memory and attention. In addition, odor identification and discrimination ability was evaluated, as well as detection threshold sensitivity for two odorants. Odor discrimination scores exhibited a significant age-related decrease. Significant age-related changes were also observed for CSERP N1P2 and P2 amplitudes, and for the N1 peak latency. The age-related decrease of CSERP amplitudes appeared to follow a different time course for responses to trigeminal and olfactory stimulants.

Body odor evoked potentials: a new method to study the chemosensory perception of self and non-self in humans.

A new method will be presented which allows the perception of body odors in humans to be studied objectively. The analysis of body odor-evoked potentials was used to investigate if and how the human brain is able to differentiate self from non-self body odor for the first time. Six subjects (three females) participated in two experimental sessions. In each session, two body odors (axillary hair) were presented within an olfactory oddball paradigm. One of the odors was collected from the subject and the other from an odor donor of the same sex. In the first session the subjects' attention was distracted to a secondary task (passive paradigm), in the second session the subjects were asked to actively differentiate the odors (active paradigm). For the EEG recordings the odors were presented within a constantly flowing airstream. The results show that the subjects could hardly differentiate the body odors subjectively. However, it could be demonstrated that the central nervous processing of one's own odor was faster than the processing of the chemosensory non-self signal. Moreover, in the active paradigm, the potentials appeared to be larger when the subjects perceived their own body odor. The conclusion is reached that the measurement of chemosensory event-related potentials (CSERP) is the method of choice for the investigation of HLA-associated body odors.

Chemosensory event-related potentials in response to trigeminal and olfactory stimulation in idiopathic Parkinson's disease.

Decrease of olfactory function in patients with Parkinson's disease (PD) has been reported by several authors. The current study investigated olfaction in PD patients using olfactory event-related potentials (OERPs) as an electrophysiologic correlate of olfactory function in combination with psychophysical testing. A specific focus was the influence of antiparkinsonian drugs. We investigated PD patients treated with antiparkinsonian drugs (n = 13) and PD patients who received no pharmacologic treatment (n = 18). They were compared to age- and sex-matched control subjects (n = 38). To obtain OERPs, stimulants were chosen to stimulate specifically the olfactory nerve (2.1 ppm vanillin, 0.8 ppm H2S). In addition, chemosomatosensory event-related potentials were recorded after trigeminal stimulation with 52% v/v CO2. Moreover, the subjects' ability to identify and to discriminate odorants was tested by means of a "squeeze bottle" technique. The study yielded the following major results: (1) Odor identification was impaired in PD patients. It was not influenced by treatment with antiparkinsonian drugs. (2) The OERP latencies were prolonged in both PD patients taking and not taking antiparkinsonian drugs; however, this effect was more pronounced in PD patients taking antiparkinsonian drugs. (3) The intranasal chemosensory trigeminal system seemingly was neither affected by the neuronal degeneration seen in PD nor by treatment with antiparkinsonian drugs.

Central processing of odor concentration is a temporal phenomenon as revealed by chemosensory event-related potentials (CSERP).

Chemosensory event-related potentials (CSERP) can be used to examine central nervous odor processing. An important question for understanding odor perception is how different concentrations are processed. In the present study two odors were chosen which activate either the olfactory (linalool) or the trigeminal (menthol) system. Both odors were presented to 11 subjects in four different concentrations. Four subjects had to attend actively to the odors while the others perceived the odors under passive attention. The results showed that increased concentrations of the olfactory stimulus resulted in shorter latencies of the N1 component but did not affect the amplitudes of the CSERP. However, the amplitudes of the stimulus dependent, exogenous components (N1, P2) increased with higher concentrations of the trigeminal stimulus. The amplitude of the late positive complex, which reflects endogenous processes, was usually larger when the odorous stimuli had to be attended to actively. It is concluded that olfactory intensity coding results in a qualitatively different but not in a stronger neuronal response of the human brain.

The effects of active and passive stimulation on chemosensory event-related potentials

During normal olfaction, stimulation is dependent upon nasal inhalation. When collecting chemosensory event-related potentials (CSERPs), inhalations may produce artifacts such as respiration-related brain potentials that confound interpretation of the data. To avoid this type of artifact, CSERPs have often been collected using stimulation that is independent of respiratory cycle. It is possible, however, that inspirations prime the olfactory tract for odor input, and traditional CSERP data acquisition techniques obscure this neural preparation. To investigate this question, twelve subjects were tested using two different approaches to stimulation. Odorants (butanol 2% and 4%) were introduced into a wanned and humidified air stream and delivered to one nostril through a cannula. In one condition, subjects mouth-breathed and stimuli occurred asynchronously with respiratory cycle (passive). In the other condition, subjects inhaled through the nose and stimuli were delivered synchronously with nasal inhalations (active). CSERP data were collected from thirty scalp sites for 3 s following stimulation. Data were corrected for eye movements, smoothed, and averaged. Maximal amplitudes for an early negativity (N1) and later positivity (P2) were determined and submitted to separate analyses of variance. These analyses indicated that administration technique interacted with both odor concentration and recording site. Additionally, amplitude of P2 was greater in the passive condition. Such results suggest that the two administration techniques produce different neural processing of olfactory stimuli and that the passive technique may be better suited for determination of the integrity of the olfactory tract for single subjects because of its greater amplitude.

Olfactory information processing during the course of the menstrual cycle

In the present study we examined whether olfactory information processing depends on the phase of the menstrual cycle. Five female subjects were investigated during three phases (follicular, ovulatory, luteal) of their menstrual cycle. In each session chemosensory (olfactory) event-related potentials (CSERP) were recorded and olfactory thresholds and the hedonic tone of the test stimulus (citral) were determined. Threshold values were correlated with the salivary cortisol level. The results show that olfactory perception changes during the menstrual cycle. After the first stimulus presentations in a recording session, odors were perceived as more complex or novel during the ovulatory period (enhanced amplitude of P3-1). With continued stimulation, odor processing became faster (reduced latency of N1, P2 and P3-2) around ovulation and slower during the follicular phase. Moreover, odors were described more differentially during the ovulatory period. Olfactory sensitivity was correlated positively with the peripheral cortisol level.

Intranasal Chemoreception in Patients with Multiple Chemical Sensitivities: A Double-Blind Investigation

Multiple chemical sensitivities (MCS) has become an increasingly frequent diagnosis assigned to patients with symptoms associated with exposures to environmental chemicals. Since the characteristic symptoms of MCS are triggered by very low concentrations of chemicals, in the range of olfactory thresholds, it is widely believed that the intranasal chemoreceptive senses are involved in the pathophysiology of MCS. Thus, the present study addressed both the olfactory and trigeminal systems; using a double-blind approach we investigated whether MCS patients show differences in responses after exposure to either room air or low concentrations of a widely used chemical agent (2-propanol). A total of 23 patients participated in the experiments (mean age 47 years; 13 female, 10 male). MCS was diagnosed according to Cullen's criteria. Performance of the nasal chemical senses was established by means of chemosensory event-related potentials (CSERP) and subjective measures of olfactory function (odor discrimination, phenylethyl alcohol odor thresholds). CSERP were recorded in response to olfactory (H2S), and trigeminal (CO2) stimuli. The study provided three major results: (1) Approximately 20% of patients diagnosed with MCS presented symptoms regardless of the type of challenge, suggesting the susceptibility of MCS patients to unspecific experimental manipulations. (2) Changes in CSERP latencies indicated a change in the processing of both olfactory and trigeminal stimuli. (3) While odor thresholds remained unchanged, the patients’ ability to discriminate odors decreased after exposure to room air. In contrast, this decrease was less pronounced after exposure to 2-prop. Summarily, MCS patients respond to challenge with 2-prop with changes of chemosensory perception which might increase their susceptibility to environmentally volatile chemicals. Changes in the pattern of event-related potentials are interpreted as the possible change of the orientation of cortical generators, i.e., neuronal populations that were involved in the processing of chemosensory information. However, investigations in healthy controls are needed in order to draw further conclusions.

Chemosensory event-related potentials in patients with temporal lobe epilepsy.

We investigated chemosensory functions in patients with temporal lobe epilepsy (TLE) to discover whether olfactory and trigeminal stimuli applied either ipsilaterally or contralaterally to the epileptic focus are processed differently. Twenty-two patients were investigated, 12 of whom had epilepsy with a focus located in left temporal lobe (LTL). The remaining 10 patients had a right temporal lobe (RTL) focus. Input from the trigeminal system was examined by use of CO2; input from the olfactory system was evaluated with vanillin and hydrogen sulfide as stimuli. Chemosensory function was assessed by evaluation of chemosensory event-related potentials (CSERP) and the patients' verbal reports in an odor identification test. In both groups of patients, prolonged CSERP latencies were noted after stimulation of the left nostril with CO2 as compared with stimulation of the right nostril. In contrast, a different pattern emerged for olfactory stimuli. After right-sided olfactory stimulation, latencies were prolonged in patients with right-sided epileptical foci. Similarly, when the left nostril was stimulated in patients with a left-sided focus, CSERP latencies were prolonged. Thus, neocortical processing of olfactory, but not trigeminally mediated information evidently is affected by functional lesions of the temporal lobe. After olfactory stimulation in patients with a right-sided focus, the distribution of amplitudes was different from normal. Moreover, analyses showed nonoverlapping 95% confidence intervals (CI) for latency N1 when vanillin was applied to the right nostril. These results indicate that RTL may play a different role in processing of olfactory information as compared with LTL.

Olfactory (Chemosensory) Event-Related Potentials

Chemosensory event-related potentials (CSERPs) have found their way into a number of fields of research where they help to determine the function of both the trigeminal and the olfactory system. The investigation of chemosensory deficits in patients with Parkinson's or Alzheimer's disease is only one of the typical applications. It can be assumed that scientists involved in research on patients with multiple chemical sensitivities will also benefit from having access to objective data covering different aspects of the sense of smell.

Suggestions for collection and reporting of chemosensory (olfactory) event-related potentials

Suggestions for collection and reporting of chemosensory (olfactory) event-related potentials

Chemosensory event-related potentials in the investigation of interactions between the olfactory and the somatosensory (trigeminal) systems

The aim of the study was to investigate the interaction of the olfactory and somatosensory systems in the perception of chemical stimuli. Stimuli were chosen so as to selectively activate the olfactory (hydrogen sulphide, H 2S) and trigeminal (carbon dioxide, CO 2) nerves. In addition, carvone was included as a stimulus with mixed properties. Thirty healthy volunteers participated in the experiments. Subjects rated the intensity of each of the stimulants when presented alone and as a component of binary mixtures. Chemosensory event-related potentials (CSERPs) were obtained from 5 recording positions. Analysis of the intensity ratings indicated that there was not difference between the 3 stimulants when used as single components. In binary mixtures intensity estimates of H 2S were suppressed by CO 2 and carvone. In addition, while estimates of CO 2 were suppressed by carvone estimates of the latter were enhanced in the same mixture. CSERP data confirmed earlier findings with regard to the topographic distribution of amplitudes, i.e., if the olfactory system had been activated largest amplitudes were observed at position Pz, whereas activation of the trigeminal nerve produced largest amplitudes at Cz. Moreover, the suppression of CO 2 estimates by carvone was reflected in a corresponding suppression of the CSERP amplitudes. In addition, when CO 2 was mixed with H 2S or carvone there was a decrease in the CSERP latency indicating interactions of both sensory systems in the time domain.

Chemosensory event-related potentials in man: relation to olfactory and painful sensations elicited by nicotine

The aim of this study was to investigate the topographical distribution of chemosensory event-related potentials in relation to stimulation with nicotine. The recognition thresholds of 3 different sensations elicited by nicotine (odor, burning, stinging) were determined. Subsequently, 3 concentrations of nicotine were applied which were just above mean threshold for each of the 3 sensations. Subjects rated the intensity of odor, burning, and stinging. Additionally, they tracked the time course of these sensations. Odor and stinging appeared immediately after stimulus onset. Burning started after several seconds. Intensity rating of burning and stinging increased with rising stimulus concentrations, whereas the odorous sensation was strongest at medium concentrations. After low and medium stimuli largest mean amplitudes were parietally obtained, whereas following stimulation with the highest concentration, amplitudes peaked at Cz.