Olfactory event-related potentials in psychosis-prone subjects

Spatiotemporal dynamics of odor representations in the human brain revealed by EEG decoding

To elucidate when and where in the brain different aspects of odor perception emerge, we decoded odors from an electroencephalogram and associated the results with perception and source activities. The odor information was decoded 100 ms after odor onset at the earliest, with its signal sources estimated in and around the olfactory areas. The neural representation of odor unpleasantness emerged 300 ms after odor onset, followed by pleasantness and perceived quality at 500 ms. During this time, brain regions representing odor information spread rapidly from the olfactory areas to regions associated with emotional, semantic, and memory processing. The results suggested that odor perception emerges through computations in these areas, with different perceptual aspects having different spatiotemporal dynamics.

How the human brain translates olfactory inputs into diverse perceptions, from pleasurable floral smells to sickening smells of decay, is one of the fundamental questions in olfaction. To examine how different aspects of olfactory perception emerge in space and time in the human brain, we performed time-resolved multivariate pattern analysis of scalp-recorded electroencephalogram responses to 10 perceptually diverse odors and associated the resulting decoding accuracies with perception and source activities. Mean decoding accuracies of odors exceeded the chance level 100 ms after odor onset and reached maxima at 350 ms. The result suggests that the neural representations of individual odors were maximally separated at 350 ms. Perceptual representations emerged following the decoding peak: unipolar unpleasantness (neutral to unpleasant) from 300 ms, and pleasantness (neutral to pleasant) and perceptual quality (applicability to verbal descriptors such as “fruity” or “flowery”) from 500 ms after odor onset, with all these perceptual representations reaching their maxima after 600 ms. A source estimation showed that the areas representing the odor information, estimated based on the decoding accuracies, were localized in and around the primary and secondary olfactory areas at 100 to 350 ms after odor onset. Odor representations then expanded into larger areas associated with emotional, semantic, and memory processing, with the activities of these later areas being significantly associated with perception. These results suggest that initial odor information coded in the olfactory areas (<350 ms) evolves into their perceptual realizations (300 to >600 ms) through computations in widely distributed cortical regions, with different perceptual aspects having different spatiotemporal dynamics.

Temporal Lobe Volume Decrements in Psychosis Spectrum Youths

Structural brain abnormalities have been amply demonstrated in schizophrenia. These include volume decrements in the perirhinal/entorhinal regions of the ventromedial temporal lobe, which comprise the primary olfactory cortex. Olfactory impairments, which are a hallmark of schizophrenia, precede the onset of illness, distinguish adolescents experiencing prodromal symptoms from healthy youths, and may predict the transition from the prodrome to frank psychosis. We therefore examined temporal lobe regional volumes in a large adolescent sample to determine if structural deficits in ventromedial temporal lobe areas were associated, not only with schizophrenia, but also with a heightened risk for psychosis. Seven temporal lobe regional volumes (amygdala [AM], hippocampus, inferior temporal gyrus, parahippocampal gyrus, superior temporal gyrus, temporal pole, and entorhinal cortex [EC]) were measured in 386 psychosis spectrum adolescents, 521 adolescents with other types of psychopathology, and 359 healthy adolescents from the Philadelphia Neurodevelopment Cohort. Total intracranial and left EC volumes, which were both smallest among the psychosis spectrum, were the only measures that distinguished all 3 groups. Left AM was also smaller in psychosis spectrum compared with healthy subjects. EC volume decrement was strongly correlated with impaired cognition and less robustly associated with heightened negative/disorganized symptoms. AM volume decrement correlated with positive symptoms (persecution/special abilities). Temporal lobe volumes classified psychosis spectrum youths with very high specificity but relatively low sensitivity. These MRI measures may therefore serve as important confirmatory biomarkers denoting a worrisome preclinical trajectory among at-risk youths, and the specific pattern of deficits may predict specific symptom profiles.

Olfaction in the psychosis prodrome: electrophysiological and behavioral measures of odor detection

Smell identification deficits (SIDs) are relatively specific to schizophrenia and its negative symptoms, and may predict transition to psychosis in clinical high-risk (CHR) individuals. Moreover, event-related potentials (ERPs) to odors are reduced in schizophrenia. This study examined whether CHR patients show SIDs and abnormal olfactory N1 and P2 potentials. ERPs (49 channels) were recorded from 21 CHR and 20 healthy participants (13 males/group; ages 13-27 years) during an odor detection task using three concentrations of hydrogen sulfide (H2S) or blank air presented unilaterally by a constant-flow olfactometer. Neuronal generator patterns underlying olfactory ERPs were identified and measured by principal components analysis (unrestricted Varimax) of reference-free current source densities (CSD). Replicating previous findings, CSD waveforms to H2S stimuli were characterized by an early N1 sink (345 ms, lateral-temporal) and a late P2 source (600 ms, mid-frontocentroparietal). N1 and P2 varied monotonically with odor intensity (strong > medium > weak) and did not differ across groups. Patients and controls also showed comparable odor detection and had normal odor identification and thresholds (Sniffin' Sticks). However, olfactory ERPs strongly reflected differences in odor intensity and detection in controls, but these associations were substantially weaker in patients. Moreover, severity of negative symptoms in patients was associated with reduced olfactory ERPs and poorer odor detection, identification and thresholds. Three patients who developed psychosis had poorer odor detection and thresholds, and marked reductions of N1 and P2. Thus, despite the lack of overall group differences, olfactory measures may be of utility in predicting transition to psychosis among CHR patients.

Networks involved in olfaction and their dynamics using independent component analysis and unified structural equation modeling

The study of human olfaction is complicated by the myriad of processing demands in conscious perceptual and emotional experiences of odors. Combining functional magnetic resonance imaging with convergent multivariate network analyses, we examined the spatiotemporal behavior of olfactory-generated blood-oxygenated-level-dependent signal in healthy adults. The experimental functional magnetic resonance imaging (fMRI) paradigm was found to offset the limitations of olfactory habituation effects and permitted the identification of five functional networks. Analysis delineated separable neuronal circuits that were spatially centered in the primary olfactory cortex, striatum, dorsolateral prefrontal cortex, rostral prefrontal cortex/anterior cingulate, and parietal-occipital junction. We hypothesize that these functional networks subserve primary perceptual, affective/motivational, and higher order olfactory-related cognitive processes. Results provided direct evidence for the existence of parallel networks with top-down modulation for olfactory processing and clearly distinguished brain activations that were sniffing-related versus odor-related. A comprehensive neurocognitive model for olfaction is presented that may be applied to broader translational studies of olfactory function, aging, and neurological disease.

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.

Responses to olfactory and intranasal trigeminal stimuli: relation to the respiratory cycle

The aim of the study was to investigate whether the perception of intranasal chemosensory stimuli changes in relation to the respiratory cycle. We investigated 40 healthy subjects with normal olfactory function who participated in four sessions. The first session was used to adapt subjects to the experimental conditions, and, specifically, to train a certain breathing technique (velopharyngeal closure) which prevents intranasal respiratory air-flow. In each of the following three sessions one of three stimulants was tested, namely phenyl ethyl alcohol (PEA), hydrogen sulfide (H(2)S), or the trigeminal stimulant carbon dioxide (CO(2)). The sequence of testing the three stimulants was randomized across all participants. Sessions were separated by at least 1 day. Chemosensory event-related potentials (ERP) were recorded in response to 80 stimuli each. Following each stimulus subjects rated its intensity using a computerized visual analogue scale. Respiration was recorded using a probe in front of the subjects' mouth. While presentation of chemosensory stimuli was performed independent of the respiratory cycle, responses were averaged off-line according to the subjects' respiratory phase when the stimuli had been presented. Intensity of olfactory or trigeminal stimuli did not differ significantly in relation to the respiratory cycle. Olfactory ERP to phenylethyl alcohol were larger when stimuli were presented during inspiration. Similarly, responses to H(2)S tended to be larger when stimuli were presented during inspiratory phases. In addition, responses to CO(2) were larger when stimuli were presented during inspiration. Differences in relation to the respiratory cycle were found specifically for early ERP components. It is important to note that the changes of chemosensory information processing were found in the absence of changes of intranasal airflow. These data indicate on an electrophysiological level that there is priming of both olfactory and trigeminally mediated sensations in relation to the respiratory cycle.

Olfactory function and schizophrenia: an update

PURPOSE OF REVIEW

Olfaction is a field of growing interest in schizophrenia research. This article reviews recent studies on olfactory functions in schizophrenia.

RECENT FINDINGS

The current literature provides additional insights into olfactory deficits, abnormalities, and olfactory hedonic dysfunction in schizophrenia. Recent findings reinforce particular associations with negative symptoms and deficit syndrome schizophrenia. Studies indicate that abnormalities in patients with schizophrenia extend to more peripheral olfactory structures and functions, including olfactory receptor neuron dysfunction. Olfactory identification ability was found to relate to prodromal disorganization symptoms in young high-risk patients. Further support for the notion of a genetic contribution to olfactory dysfunction in schizophrenia derives from studies reporting physiological olfactory dysfunction (olfactory event-related potentials) in unaffected relatives, and an odor-specific hyposmia, present in both patients with schizophrenia and family members.

SUMMARY

Further research is needed to improve our understanding of olfactory dysfunction in schizophrenia. Recent encouraging findings underscore that the olfactory system is a field of research that holds promise for advancing our understanding of the pathophysiology of schizophrenia and possibly as a useful endophenotypic marker of neurodevelopmental vulnerability.

Scents and nonsense: olfactory dysfunction in schizophrenia

Among the sensory modalities, olfaction is most closely associated with the frontal and temporal brain regions that are implicated in schizophrenia and most intimately related to the affective and mnemonic functions that these regions subserve. Olfactory probes may therefore be ideal tools through which to assess the structural and functional integrity of the neural substrates that underlie disease-related cognitive and emotional disturbances. Perhaps more importantly, to the extent that early sensory afferents are also disrupted in schizophrenia, the olfactory system-owing to its strategic anatomic location-may be especially vulnerable to such disruption. Olfactory dysfunction may therefore be a sensitive indicator of schizophrenia pathology and may even serve as an "early warning" sign of disease vulnerability or onset. In this article, we review the evidence supporting a primary olfactory sensory disturbance in schizophrenia. Convergent data indicate that structural and functional abnormalities extend from the cortex to the most peripheral elements of the olfactory system. These reflect, in part, a genetically mediated neurodevelopmental etiology. Gross structural and functional anomalies are mirrored by cellular and molecular abnormalities that suggest decreased or faulty innervation and/or dysregulation of intracellular signaling. A unifying mechanistic hypothesis may be the epigenetic regulation of gene expression. With the opportunity to obtain olfactory neural tissue from live patients through nasal epithelial biopsy, the peripheral olfactory system offers a uniquely accessible window through which the pathophysiological antecedents and sequelae of schizophrenia may be observed. This could help to clarify underlying brain mechanisms and facilitate identification of clinically relevant biomarkers.

Olfactory Discrimination and Transient Mood Change in Young Men and Women: Variation by Season, Mood State, and Time of Day

Odor performance varies by clinical state and gender, though little is known about its variation by season or time of day. Many odors, including lavender, induce transient mood changes. This study explored discrimination differences between various lavender oil blends and their effects on transient mood in the morning and evening in depressed and nondepressed adults. We also determined seasonal influences on these measures. A total of 169 subjects, 98 women and 71 men (mean age +/- SD, 19.3 +/- 1.6 y) participated, with different subjects studied at different times of the year. The Beck Depression Inventory (BDI) classified subjects as depressed (score > or =10; N= 57) or nondepressed (score <10; N= 112). In the discrimination test, subjects compared pairs of two different lavender oil blends or a control. Transient change in mood was assessed by the Profile of Mood States (POMS) after each trial of five lavender blends interspersed by three control odors. Tests were conducted in the morning (08:00-10:00 h) and evening (18:00-20:00h). In all subjects, discrimination was significantly better for some odor pairs than for others, thus demonstrating test specificity. Discrimination was better overall in the fall than winter/spring and better in depressed than nondepressed subjects for specific odor pairs. No significant gender or time-of-day differences in discriminability were detected. There were, however, significant group differences in transient mood profiles. Current depressed state affected mood response, with lavender increasing anger in depressed subjects only. In addition, depressed subjects and men, whether or not depressed, exhibited diurnal mood variation, with better mood in the evening; the former group also showed more evening energy. All subjects were more confused in the morning than evening. Season also affected transient mood; winter/spring-tested subjects reported more vigor than fall-tested subjects. In addition, summer-tested subjects showed more tension in the morning, whereas fall-tested subjects showed the opposite pattern in the evening. In all subjects, lavender increased fatigue, tension, confusion, and total mood disturbance, and it decreased vigor. The study showed that both chronobiological (seasonal and time-of-day) and clinical factors modify discrimination and mood response to odors. Brief lavender odor presentation may serve as a nonphotic method for altering mood in young depressed and nondepressed adults particularly during the fall, a time of heightened discriminability.

Sex differences and reproductive hormone influences on human odor perception

The question of whether men and women differ in their ability to smell has been the topic of scientific investigation for over a hundred years. Although conflicting findings abound, most studies suggest that, for at least some odorants, women outperform men on tests of odor detection, identification, discrimination, and memory. Most functional imaging and electrophysiological studies similarly imply that, when sex differences are present, they favor women. In this review we examine what is known about sex-related alterations in human smell function, including influences of the menstrual cycle, pregnancy, gonadectomy, and hormone replacement therapy on a range of olfactory measures. We conclude that the relationship between reproductive hormones and human olfactory function is complex and that simple associations between circulating levels of gonadal hormones and measures of olfactory function are rarely present.

Olfaction: a potential cognitive marker of psychiatric disorders

Cognitive deficits are well documented in psychiatric disorders, particularly in schizophrenia and depression. Cognitive activity roots in perceptions. However, research on sensorial alterations in psychiatric conditions has mainly focused on visual or auditory processes and less on olfaction. Here, we examine data on olfactory deficits in psychiatric patients using a systematic review of recent publications. Schizophrenic patients are mainly characterized by no reliable change in odour sensitivity and by a deficit in odour identification, recognition and discrimination. Depressed patients principally exhibit a deficit in the hedonic aspects of this perception, even if, in some case, alterations in sensitivity or identification are also found. Changes in odour perception are also found in dementia and in some neurodegenerative disease, but in this case alterations concern all aspects of the sensorial experience (detection threshold, identification and recognition). Taken together, these data indicate that olfactory abnormalities might be a marker of psychiatric conditions, with a specific pattern for each disease.

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.

Thresholds and chemosensory event-related potentials to malodors before, during, and after puberty: differences related to sex and age

A sex-related difference in olfactory sensitivity to androstadienone and androstenone has been reported to occur during puberty. The study reported here extends this work to investigate whether sex and age differences exist before, during, and after puberty for 2-methyl, 3-mercapto-butanol (2M3M; a malodorous component of human sweat), carbon disulfide/hydrogen sulfide (H2S), and androstadienone. A total of 121 participants took part in the study (58 females, 63 males; age range 9-20 years). Participants were divided into 3 groups (i) pre-puberty, (ii) puberty and (iii) post-puberty. Threshold measurements for (i) androstadienone, (ii) 2M3M and (iii) carbon disulfide were recorded. Chemosensory event-related potentials (CSERPs) were recorded using air-dilution olfactometry. The results revealed that female thresholds for the three odorants were stable between the three age groups. Pubescent males had higher thresholds (less sensitive) for all three odorants. In the post-puberty group, sex differences were only observed for 2M3M. These differences are mirrored by significant sex differences for CSERP latencies. The latency increase in male pubescents may be due to the production of sweat by the apocrine glands resulting in increased levels of 2M3M and androstadienone, resulting in adaptation. To conclude, based on the present study performed in a relatively large sample, the processing of malodors in males is different from that of females during puberty. This observation not only relates to a reduced sensitivity towards odors typially found in axillary sweat but also extends towards other malodors. While the underlying cause may be partly due to specific adaptation towards malodors present in axillary sweat it might also reflect hormonal changes modifying the perception of odors.

Signal-to-noise ratio of chemosensory event-related potentials

OBJECTIVE

We investigated the influence of the number of stimuli on signal-to-noise (S/N) ratio of CSERP.

METHODS

CSERP from 20 normosmic subjects were obtained in response to stimulation with two olfactory (H(2)S and PEA) and a trigeminal (CO(2)) stimulant. For each of these odors, 160 stimuli were delivered into the right nostril (duration 200ms, mean ISI 30s) using a constant-flow, air-dilution olfactometer. For each EEG recording site (Fz, Cz, Pz, C3, C4), peak-to-peak amplitude N1P2 and noise amplitude levels were determined. Subsequently, S/N ratios were calculated.

RESULTS

The S/N ratios for olfactory ERP generally improved for H(2)S and PEA. For responses to PEA, S/N ratios increased significantly up to 80 averages (S/N ratio=5.6). The number of stimuli for an optimal S/N ratio for trigeminal ERP was slightly lower, i.e. 60 averages (S/N ratio=7.9).

CONCLUSIONS

S/N N1P2 ratios in olfactory and trigeminal ERP significantly improve with an increasing number of responses averaged under these experimental conditions. This is mainly due to a reduction of noise level. Applying more stimuli has little additional effect on S/N ratio due to a concomitant decrease in signal amplitude.

SIGNIFICANCE

An optimal S/N ratio is essential when recording CSERP in neurodegenerative disorders, where responses may be of low amplitude, and for medico-legal purposes.

Sleep changes vary by odor perception in young adults

Peppermint, a stimulating odor, increases alertness while awake and therefore may inhibit sleep. This study examined peppermint's effects on polysomnographic (PSG) sleep, alertness, and mood when presented before bedtime. Twenty-one healthy sleepers (mean age +/- S.D., 20.1 +/- 2.0 years) completed three consecutive laboratory sessions (adaptation, control, and stimulus nights). Peppermint reduced fatigue and improved mood and was rated as more pleasant, intense, stimulating, and elating than water. These perceptual qualities associated with sleep measures: subjects rating peppermint as very intense had more total sleep than those rating it as moderately intense, and also showed more slow-wave sleep (SWS) in the peppermint than control session. Furthermore, subjects who found peppermint stimulating showed more NREM and less REM sleep while those rating it as sedating took longer to reach SWS. Peppermint did not affect PSG sleep, however, when these perceptual qualities were not considered. Peppermint also produced gender-differentiated responses: it increased NREM sleep in women, but not men, and alertness in men, but not women, compared with the control. Thus, psychological factors, including individual differences in odor perception play an important role in physiological sleep and self-rated mood and alertness changes.

An olfactory stimulus modifies nighttime sleep in young men and women

Aromatherapy is an anecdotal method for modifying sleep and mood. However, whether olfactory exposure to essential oils affects night-time objective sleep remains untested. Previous studies also demonstrate superior olfactory abilities in women. Therefore, this study investigated the effects of an olfactory stimulus on subsequent sleep and assessed gender differences in such effects. Thirty-one young healthy sleepers (16 men and 15 women, aged 18 to 30 yr, mean+/-SD, 20.5+/-2.4 yr) completed 3 consecutive overnight sessions in a sleep laboratory: one adaptation, one stimulus, and one control night (the latter 2 nights in counterbalanced order). Subjects received an intermittent presentation (first 2 min of each 10 min interval) of an olfactory (lavender oil) or a control (distilled water) stimulus between 23:10 and 23:40 h. Standard polysomnographic sleep and self-rated sleepiness and mood data were collected. Lavender increased the percentage of deep or slow-wave sleep (SWS) in men and women. All subjects reported higher vigor the morning after lavender exposure, corroborating the restorative SWS increase. Lavender also increased stage 2 (light) sleep, and decreased rapid-eye movement (REM) sleep and the amount of time to reach wake after first falling asleep (wake after sleep onset latency) in women, with opposite effects in men. Thus, lavender serves as a mild sedative and has practical applications as a novel, nonphotic method for promoting deep sleep in young men and women and for producing gender-dependent sleep effects.

Left temporo-limbic and orbital dysfunction in schizophrenia during odor familiarity and hedonicity judgments

Impairments of olfactory processing in patients with schizophrenia (SZ) have been reported in various olfactory tasks such as detection, discrimination, recognition memory, identification, and naming. The purpose of our study was to determine whether impairments in odor familiarity and hedonicity judgments observed in SZ patients during a previous behavioral study are associated with modifications of the activation patterns in olfactory areas. Twelve SZ patients, and 12 healthy comparison (HC) subjects, were tested using the H2(15)O-PET technique and 48 different odorants delivered during 8 scans. In addition to an odorless baseline condition, they had either to detect odor, or to judge odor familiarity or hedonicity, giving their responses by pressing a button. Regional cerebral blood flows during olfactory conditions were compared with those for baseline condition. Between-group analyses were then performed, and completed by regions of interest analyses. Both groups had equivalent ability for the detection of suprathreshold odorants, but patients found odors less familiar, and pleasant odors less pleasant than HC subjects. These behavioral results were related to functional abnormalities in temporo-limbic and orbital olfactory regions lateralized in the left hemisphere: the posterior part of the piriform cortex and orbital regions for familiarity judgments, the insular gyrus for hedonicity judgments, and the left inferior frontal gyrus and anterior piriform cortex/putamen region for the three olfactory tasks. They mainly resulted from a lack of activation during task conditions in the SZ patients. These data could explain olfactory disturbances and other clinical features of schizophrenia such as anhedonia.

Scent of a disorder: olfactory functioning in schizophrenia

The use of olfactory probes to assess frontal and temporal-limbic system functioning in patients with schizophrenia has garnered increasing interest among basic and clinical investigators. Deficits in odor identification, detection threshold sensitivity, discrimination, and memory have been reported and are thought to represent a centrally mediated deficit in the processing of this information. These impairments are seen in affected probands, first-degree family members, and those at risk for developing the illness, suggesting a genetic vulnerability or predisposition to chemosensory abnormalities. The observed deficits are not explained by gender, medication use, cognitive impairment, or smoking status, and support the hypothesis of primary dysfunction in the olfactory system. Along this same line, structural abnormalities in the peripheral and central olfactory brain regions, as well as disruptions of the basic physiology of this system, have been described. The study of olfactory processing in schizophrenia has already advanced the knowledge of the neural substrate for this disorder. Because the olfactory system continuously regenerates throughout life, it allows for a unique view of an ongoing neurodevelopmental process.

Physiologic impairment of olfactory stimulus processing in schizophrenia

BACKGROUND

Behavioral studies of olfaction have demonstrated impairments in the ability to detect and identify odors in patients with schizophrenia. These deficits appear to be independent of either symptom severity or other cognitive impairment. Only limited efforts have been made to investigate the neurophysiologic substrate of these olfactory abnormalities. This article reports the first examination of olfactory electrophysiologic responses in patients with schizophrenia.

METHODS

Olfactory event-related potential responses to three different concentrations of hydrogen sulfide were recorded in a sample of 21 patients and 20 healthy control subjects. Odors were presented via an olfactometer to ensure there was no associated trigeminal nerve stimulation.

RESULTS

Patients exhibited abnormalities in the amplitudes of the N1 and P2 components of the olfactory evoked potential, and delayed latency of the P2. The N1 abnormality, which denotes primary olfactory cortex activity, was related to impaired odor detection threshold sensitivity; the P2 abnormality was related to impaired odor identification.

CONCLUSIONS

These data indicate the presence of a primary physiologic impairment in the olfactory cortex underlying behavioral olfactory deficits seen in patients with schizophrenia. This is consistent with postmortem and in vitro studies suggesting abnormalities in olfactory receptor neurons. Understanding the nature of these physiologic olfactory impairments could offer clues to the basic neuropathology of this disorder.

Modulation of visual event-related potentials by emotional olfactory stimuli

The objective of the present study was to determine whether an olfactory prime could modulate behavior and visual event-related potentials (ERPs) obtained in response to a visual stimulation representing female faces. More specifically, we tested the hypothesis that a pleasant odor could have effects on face perception: behavioral effects on subjective emotional estimation of faces, and on associated response times, and electrophysiological effects on the N400 and late positive complex or LPC. Experiments were performed in which subjects had to decide whether the presented face was pleasant or not, while visual ERPs were recorded. Faces were always primed with either a pleasant odor or a neutral olfactory stimulus (pure air). In order to test the effect of subject's awareness, participants were not informed that an odor would be presented in the experimental sessions. Responses were significantly shorter for unpleasant faces. However, no behavioral effects of the pleasant odor on response time or on evaluation of face pleasantness were observed. Late ERPs evoked by faces were modulated by the presence of a pleasant odor, even when subjects were neither warned nor aware of the presence of the odor: in a frontal site and after the diffusion of the odor, the LPC (appearing 550 ms after the presentation of the visual stimulus) evoked by unpleasant faces was significantly more positive than the LPC evoked by pleasant faces. This effect could reflect an enhanced alert reaction to unpleasant faces are preceded by an (incongrous) pleasant odor.

Olfactory Modulation of Steady- State Visual Evoked Potential Topography in Comparison with Differences in Odor Sensitivity

Summary Research was undertaken to determine whether olfactory stimulation can alter steady-state visual evoked potential (SSVEP) topography. Odor-air and air-only stimuli were used to determine whether the SSVEP would be altered when odor was present. Comparisons were also made of the topographic activation associated with air and odor stimulation, with the view toward determining whether the revealed topographic activity would differentiate levels of olfactory sensitivity by clearly identifying supra- and subthreshold odor responses. Using a continuous respiration olfactometer (CRO) to precisely deliver an odor or air stimulus synchronously with the natural respiration, air or odor (n-butanol) was randomly delivered into the inspiratory airstream during the simultaneous recording of SSVEPs and subjective behavioral responses. Subjects were placed in groups based on subjective odor detection response: “yes” and “no” detection groups. In comparison to air, SSVEP topography revealed cortical changes in response to odor stimulation for both response groups, with topographic changes evident for those unable to perceive the odor, showing the presence of a subconscious physiological odor detection response. Differences in regional SSVEP topography were shown for those who reported smelling the odor compared with those who remained unaware of the odor. These changes revealed olfactory modulation of SSVEP topography related to odor awareness and sensitivity and therefore odor concentration relative to thresholds.

Exploring the latent structure of the Perceptual Aberration, Magical Ideation, and Physical Anhedonia Scales in a German sample

The schizotypy model proposed by Meehl (1990) assumes a discontinuous distribution of schizophrenia liability. The "schizogene" is thought to determine if one is at risk for psychosis (i.e., whether one is a member of the taxon or its complement, which are considered to be the two latent classes). Using a German non-student sample (n = 809) we wanted to (1) replicate the results of prior research pertaining to the latent structure and base rate of schizotypy assessed by the Perceptual Aberration Scale (PER; Chapman, Chapman, & Raulin, 1978), and (2) investigate whether the same holds true for two other prominent psychometric indices, the Magical Ideation Scale (MI; Eckblad & Chapman, 1983) and the Physical Anhedonia Scale (PhA; Chapman et al., 1976), if one uses the same kind of analysis--the MAXCOV-HITMAX analysis based on subsets of items (Meehl, 1973). Pertaining to PER and PhA, our results are in accordance with prior research showing a latent class structure and a base rate of about 12% for schizotypy. However, for MI, there was no evidence of a taxonic structure. Possible reasons for MI's negative results are discussed as well as the role of the concept "anhedonia."

Olfactory and trigeminal event-related potentials in migraine

BACKGROUND

Trigeminal/neuronal hyperexcitability and spreading depression activating the trigemino-vascular system are discussed in migraine-pathophysiology. This study investigated trigeminal and olfactory event-related potentials in migraineurs.

METHODS

Nasal chemosensitivity was assessed in 19 female migraineurs with or without aura > 72 h before or after an attack and in 19 healthy females employing event-related cortical potentials (ERPs) after specific trigeminal stimulation of nasal nociceptors with short pulses of CO2, and specific olfactory stimulation with H2S. Odour thresholds and odour identification performance were also tested.

RESULTS

Migraineurs exhibited greater responses to trigeminal stimulation, indicated by significantly larger ERP amplitudes N1. In contrast, olfactory ERP amplitudes P1N1 were significantly smaller in migraineurs. A leave-one-out classification procedure on the basis of these two parameters assigned 76.3% cases correctly. The olfactory ERP amplitude discriminated better between groups than trigeminal ERPs (71.1 vs. 68.4% correct classification).

CONCLUSIONS

Our data suggest trigeminal hyperexcitability in migraineurs. A general increase of nasal chemosensitivity is not supported because of smaller olfactory ERP amplitudes in migraineurs. Olfactory ERPs discriminate better than trigeminal ERPs between migraineurs and controls, emphasizing the significance of the olfactory system in migraine.

Asymmetrical olfactory acuity and neuroleptic treatment in schizophrenia

Uni-rhinal olfactory acuity in schizophrenia was investigated in two experiments. The first assessed the presence of a predicted atypical asymmetry of nostril laterality and the second assessed the effect of antipsychotic treatment on the asymmetry. Although olfactory identification impairment has been well documented in schizophrenia, olfactory acuity has been neglected. This may be an oversight as cerebral structures of the mesial temporal lobe important to olfactory perception have often been implicated in the pathophysiology of schizophrenia and it is thus reasonable to postulate a primary impairment of olfactory acuity in schizophrenia. In addition, unmedicated patients with schizophrenia have exhibited asymmetrical laterality favouring the right over the left hemisphere in studies of visual, haptic, and auditory perception, and the few published prospective treatment studies have suggested a reversal of this asymmetry with first generation neuroleptic treatments. In experiment 1 a generalization of the perceptual asymmetry to olfactory acuity was examined by measurement of n-butanol olfactory thresholds with the Connecticut Chemosensory Perception Exam (CCPE) in an unmedicated sample of 17 patients with schizophrenia and 17 age, gender, and handedness matched normal controls. The patient sample showed an asymmetrical impairment of the left nostril that was not apparent in the normal control sample. In experiment 2, the CCPE was administered to a new sample of 10 patients with schizophrenia before and after neuroleptic treatment. The asymmetry observed in experiment 1 was replicated, and the relative advantage of the right nostril shifted to a relative advantage of the left nostril over the course of 8weeks of treatment. Results are discussed in relation to cerebral aspects of schizophrenia and potential implications to cognitive change from treatment.

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.

Two-year stability of Psychosis Proneness Scales and their relations to personality disorder traits

Two-year stability of Physical Anhedonia (PhA), Perceptual Aberration (PER), and Magical Ideation (MI) scale scores and their relation to personality disorder traits were examined. Additionally, the effects of a time-lagged (prospective) versus concurrent measurement of psychosis proneness and personality disorder traits were studied to examine the specificity of MI, PER, and PhA. With a non-college-student sample (n = 404), stability for PhA was sufficiently high, but for PER and MI, stability was moderate to low. The correlations between personality disorder traits and psychosis proneness scales demonstrate that simultaneous assessment leads to a more nonspecific pattern of associations for MI and PER, although the correlation to schizotypal personality disorder traits were the highest. However, prospectively only MI, but neither PER nor PhA, emerged as a significant predictor for schizotypal and paranoid personality disorder traits in multiple-regression analysis. This suggests that MI may allow for a more specific assessment of psychosis proneness than PER.

Olfactory event-related potentials to amyl acetate in congenital anosmia

Olfactory function was evaluated by olfactory event-related potentials and standardized psychophysical measures including the Smell Identification Test and odor detection threshold tests for 3 chemosensory stimulants in 9 subjects with isolated congenital anosmia and 9 age- and gender-matched normosmic controls. There was a significant difference in Smell Identification Test scores (P < 0.001) and odor detection thresholds for phenylethyl alcohol (P < 0.001) and isoamyl acetate (P < 0.001) between the anosmic and normosmic subjects. Detection thresholds for chloracetyl phenone, a trigeminal stimulant, did not differ between the 2 groups. Olfactory evoked potentials were recorded in response to amyl acetate and air control stimuli presented at volume flow rate of 5 l/min, stimulus duration of 40 ms, and randomized interstimulus intervals of 6-30 s. In the control subjects, evoked potentials to amyl acetate were characterized by 4 reproducible components (P1, N1, P2, and N2). In the subjects with congenital anosmia, no reproducible evoked potential components were identified in response to amyl acetate. No reproducible evoked potential components were seen in response to the air control stimulus in either the anosmic or normosmic groups. These data suggest that olfactory evoked potentials provide a specific measure of olfactory function.

Olfactory event-related potentials in normal human subjects: effects of age and gender

Behavioral and electrophysiological testing of olfactory function was performed in 33 normal human male and female subjects, 18-83 years of age. Acuity for odor identification and odor detection was verified by standard psychophysical tests. For evoked potential testing, a constant flow olfactometer provided odorant stimuli (amyl acetate) or air control stimuli that were presented to the right nostril by a nasal cannula at a flow rate of 5 l/min, duration of 40 msec and random interstimulus intervals of 6-30 sec. The behavioral tests revealed no significant difference between males and females, whereas increasing age was associated with a decline in performance on the odor identification test. No reproducible evoked potentials were recorded in response to the air control stimulus. Potentials to the odorant stimulus consisted of 4 components named P1, N1, P2 and N2. A significant correlation was found between P2 latency and odor identification test scores, suggesting a relationship between the generation of the P2 component and olfactory processing. P2 peak latency increased significantly with age at 2.5 msec/year. An age-related decline in N1-P2 interpeak amplitude was seen in male subjects. Topographic differences were seen in the P2 peak amplitude and the N1-P2 and P2-N2 interpeak amplitudes such that their amplitudes were greatest at Cz and Pz. On average, N1-P2 interpeak amplitudes were larger in the female subjects than in the male subjects, possibly revealing a hormonal influence on the olfactory event-related potential.