Reduced olfactory performance in patients with major depression.

The aim of the present study is to investigate olfactory sensitivity and odor evaluations in a homogeneous sample of unipolar depressive patients using pure olfactory odors. Twenty-four in-patients with major depressive disorder (MDD) were investigated during their acute depressive phase. Eighteen of them participated a second time after successful treatment. A group of healthy subjects, matched by age, sex, and smoking behavior, served as a control. Olfactory sensitivity, as measured by threshold tests, was strongly reduced in patients with severe depression. Additional correlative analyses revealed that the lowered sensitivity could partly be predicted by high depression scores. After successful medical treatment, these sensitivity differences were reduced and did not reach the significance level. The subjective odor evaluations (valence and intensity ratings) were not markedly changed in general. The results reveal that olfactory performance in MDD patients is reduced at an early perceptional level of stimulus processing. It is discussed whether this effect can be attributed to the close functional connection between the main olfactory bulb and the amygdala.

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.

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.

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.

[Inducibility of olfactory sensitivity by odor exposure of persons with specific anosmia]. / Induzierbarkeit geruchlicher Sensitivität durch Duft-Exposition bei Personen mit spezifischer Anosmie.

Insensitivity to single odors, called specific anosmia, has been repeatedly reported in the literature. The main question of the present study was whether olfactory sensitivity is inducable in subjects with specific anosmia. For this reason the olfactory sensitivity of women with specific anosmia to the volatile steroid androstenone was investigated by threshold measurements at two times, before and after repeated odor exposure. Androstenone is a compound that contributes to human body odor and is found at a higher concentration in male axillary sweat than in female sweat. The results show that in more than 80% of the odor exposed anosmics olfactory perception of androstenone could be induced.

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.

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.

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.

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.

Fractionation and bioassay of human odor types.

Human urine samples were fractionated to examine the contribution of volatiles to the individual body odor. The samples were obtained from 4 male donors and fractionated using a vacuum technique. The volatiles from the chemical fractions were analyzed using the CLSA technique and gas chromatography. Thereafter, these fractions were tested in a computer-controlled olfactometer by trained rats. Although the rats were able to discriminate the distillation residue, they could not recognize the urine odor in the distilled fraction. The results of gas chromatography indicate a continuous release of volatile constituents in the distillation residue.

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.

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 NI, 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.

The nature of the late positive complex within the olfactory event-related potential (OERP).

The olfactory event-related potential (OERP) has been described as being dependent on exogenous stimulus features, but no effort has been made to examine possible endogenous determinants. We wanted to separate exogenous and endogenous components of the OERP by using an olfactory oddball paradigm. A high concentration of citral was used as the target stimulus, and a low concentration was used as the standard stimulus. Odors were presented within a constantly flowing air stream. We found that the early components of the OERP (N1, P2) are modulated by the stimulus concentration, whereas the late positive components (P3-1, P3-2) vary depending on the subjective stimulus significance and stimulus probability. It is concluded that the positive component of the OERP, which has been formerly explained by chemical and physical stimulus features, is actually determined by endogenous processes.

Analgesic effect of ceruletide in men is limited to specific pain qualities.

Cholecystokinin (CCK) and related peptides are supposed to be potent analgesic neuropeptides. Studies in rodents suggest a dose-dependent biphasic effect. The present study aimed to examine the pain modulating effect of different doses (0.5 microgram and 5 micrograms) of ceruletide (CRL), infused i.v. for 30 min. Pain thresholds were obtained for ischemic, mechanical, and thermal pain. In addition, pain tolerance was measured for mechanical pain. According to a placebo-controlled double-blind within-subject design 25 healthy men attended three experimental sessions each. Pain perception was measured as a baseline and twice after the infusion. The effect of both doses of CRL to enhance the pain threshold for thermal stimuli is in line with former studies. However, perception of heat stimuli above or below the threshold was not substantially affected by CRL treatment. Algesic properties of CRL are also indicated, because the tolerance for mechanical pain decreased after administration of the high dose of CRL. Perception of ischemic pain was not obviously influenced by any of the treatments. The role of CRL in human pain modulation seems to vary, depending on the type of experimental pain.

Modulation of pain perception in man by a vasopressin analogue.

The aim of the present experiment was to test whether vasopressin modulates pain perception in man. Twenty-four male volunteers participated in four sessions, each 2 weeks apart. After an adaptation session the subjects were treated intranasally with either 30 or 60 micrograms desmopressin (DDAVP) or placebo according to a cross-over double-blind design. Pain induction involved mechanical, thermal, and ischemic stimulation DDAVP had no unitary effects on pain perception in the different pain tests. The 30 micrograms dose induced sensitization to thermal stimuli. Neither treatment influenced ischemic pain perception. The mechanical pain threshold of the index finger was increased by the 60 micrograms dose only. After treatment with either dosage of DDAVP the subjects generally tolerated the pressure on their index finger for a longer time than after placebo treatment.