Bernfried Sojka

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.

Chemosensory anxiety signals augment the startle reflex in humans.

The aim of the present study was to investigate whether chemosensory anxiety signals can activate behavioral withdrawal systems in humans. Twelve male university students donated their axillary sweat in two situations: right before an oral academic examination (anxiety condition) and during ergometric training (exercise condition). Subjective ratings revealed that the odor donors experienced significantly more anxiety and less pleasure during the anxiety condition than during the exercise condition. Seven subjects (three females) participated in the psychophysiological experiment. The chemosensory stimuli from pooled sweat samples of the donors, and from unused cotton pads (pad condition) were presented via a constant-flow olfactometer. Acoustic startle probes (100 dB (A)) were delivered during and between the presentations of the chemosensory stimuli. Only three subjects were able to discriminate the chemosensory stimuli of the human sweat samples from room air. However, the startle reflex amplitude (EMG of the eyeblink response) recorded in the context of chemosensory anxiety signals was increased, as compared to the amplitude recorded in the context of chemosensory stimuli from either exercise (p = 0.018) or cotton pad (p = 0.012). It is concluded that chemosensory anxiety signals may pre-attentively prime defensive behavior.

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.

The double-priming paradigm: A tool for analyzing the functional significance of endogenous event-related brain potentials

A new paradigm to study the functional significance of P300 is presented. Its advantages are: The precise definition and manipulation of cognitive operations which are triggered by the very same events as used for ERP extraction; and a systematic control over the probability of events known to affect endogenous event-related potential components (probabilities of single events, event categories, and event sequences). By employing the paradigm in two experiments with visual stimuli, three subcomponents of P300 were identified: P3a; P3b; and positive Slow Wave (pSW). Experimental manipulations revealed that P3b is related to the information processing resources required to alter a perceptual set and pSW to the resources required when abstract information permanently stored in memory must be retrieved. The data further revealed that the same-different disparity in response latency for matching letters has at least two ERP correlates: A difference in P3b latency; and a difference in the amplitude of a negative recess between P3a and P3b.

When perceptual or motor sets are changed: effects of updating demands on structure and energy of P300.

Abstract It was attempted to disentangle the effect of two updating processes on P300. Three conditions were created by a priming paradigm: (1) No updating, (2) updating perceptual but no motor information, and (3) updating both perceptual and motor information. As expected, both updating conditions led to a P300-complex with more energy, but the additional demand of motor updating did not affect P300. Effects were similar for both delayed (experiment 1) and immediate responding (experiment 2). Both experiments confirmed earlier observations that P300 consists of at least three subcomponents, namely P3a, P3b, and a positive Slow Wave (pSW). Perceptual updating affected in particular the energy of P3b and pSW. Further, pSW was related to the complexity of the updating operations. When stimuli consisted of abstract symbols there was more energy in pSW than when stimuli were concrete symbols with direct spatial relations to the response. The structure and energy changes of P300 suggest that P3b and pSW do not provide an unambiguous picture of the underlying source structure. In some conditions only one peak (P3b) was observed in the surface structure; this still seemed to be the result of two underlying waves. In other conditions these waves were separated in time showing a clear double peak in the surface structure.

Delineation of Pharmacopsychological Effects by means of Endogenous Event-Related Brain Potentials: an Exemplification with Flupentixol

A new experimental paradigm for studying cognitive functions by means of endogenous event-related brain potentials is presented. The paradigm has the following characteristics: (1) subcomponents of P300 (P3a, P3b, positive slow wave) and subcomponents of CNV (early and late wave) are separated in time; (2) probability effects known to work on P300 subcomponents are completely under experimental control; and (3) psychologically defined antecedent conditions which affect particular endogenous components can be manipulated precisely and independently of each other. The usefulness of the paradigm for monitoring pharmacopsychological effects on cognitive functions is exemplified by means of flupentixol (Fluanxol 0.5). Reliable drug effects were observed with a dosage of 2 mg/day after 4 days of treatment. The results can be taken as evidence that flupentixol has an impairing effect on human information processing resources; in particular functions related to motor preparation, perceptual analysis, and memory retrieval are affected.

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.

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 ones 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.

Is There a Mismatch Negativity Analogue in the Olfactory Event-Related Potential?

Abstract The mismatch negativity (MMN) is thought to indicate automatic stimulus discrimination in response to acoustic stimuli. In the present study six male subjects were presented with the odors linalool and eugenol within a passive oddball-paradigm. The subjects were instructed to ignore the odors and concentrate on an auditory distractor task. In two sessions each odor served once as the standard stimulus and once as the deviant stimulus. Both odors when presented as deviants led to a negative deflection of the olfactory event-related potential (OERP) between 500-600 ms. After 600 ms the waveforms in response to the deviants were differentially influenced by odor quality. Although the present study should be understood as exploratory, the results suggest the existence of an early mismatch detector in the olfactory modality independent of attention and odor quality.

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.