Enhancing allocation of visual attention with emotional cues presented in two sensory modalities.

BACKGROUND: Responses to a visual target stimulus in an exogenous spatial cueing paradigm are usually faster if cue and target occur in the same rather than in different locations (i.e., valid vs. invalid), although perceptual conditions for cue and target processing are otherwise equivalent. This cueing validity effect can be increased by adding emotional (task-unrelated) content to the cue. In contrast, adding a secondary non-emotional sensory modality to the cue (bimodal), has not consistently yielded increased cueing effects in previous studies. Here, we examined the interplay of bimodally presented cue content (i.e., emotional vs. neutral), by using combined visual-auditory cues. Specifically, the current ERP-study investigated whether bimodal presentation of fear-related content amplifies deployment of spatial attention to the cued location. RESULTS: A behavioral cueing validity effect occurred selectively in trials in which both aspects of the cue (i.e., face and voice) were related to fear. Likewise, the posterior contra-ipsilateral P1-activity in valid trials was significantly larger when both cues were fear-related than in all other cue conditions. Although the P3a component appeared uniformly increased in invalidly cued trials, regardless of cue content, a positive LPC deflection, starting about 450 ms after target onset, was, again, maximal for the validity contrast in trials associated with bimodal presentation of fear-related cues. CONCLUSIONS: Simultaneous presentation of fear-related stimulus information in the visual and auditory modality appears to increase sustained visual attention (impairing disengagement of attention from the cued location) and to affect relatively late stages of target processing.

A short-term inhalation study to assess the reversibility of sensory irritation in human volunteers.

Sensory irritation is an acute adverse effect caused by chemicals that stimulate chemoreceptors of the upper respiratory tract or the mucous membranes of the outer eye. The avoidance of this end point is of uttermost importance in regulatory toxicology. In this study, repeated exposures to ethyl acrylate were analyzed to investigate possible carryover effects from day to day for different markers of sensory irritation. Thirty healthy subjects were exposed for 4 h on five subsequent days to ethyl acrylate at concentrations permitted by the German occupational exposure limit at the time of study. Ratings of eye irritation as well as eye blinking frequencies indicate the elicitation of sensory irritation. These markers of sensory irritation showed a distinct time course on every single day. However, cumulative carryover effects could not be identified across the week for any marker. The rhinological and biochemical markers could not reveal hints for more pronounced sensory irritation. Neither increased markers of neurogenic inflammation nor markers of immune response could be identified. Furthermore, the performance on neurobehavioral tests was not affected by ethyl acrylate and despite the strong odor of ethyl acrylate the participants improved their performances from day to day. While the affected physiological marker, the increased eye blinking frequency stays roughly on the same level across the week, subjective markers like perception of eye irritation decrease slightly from day to day though the temporal pattern of, i.e., eye irritation perception stays the same on each day. A hypothetical model of eye irritation time course derived from PK/PD modeling of the rabbit eye could explain the within-day time course of eye irritation ratings repeatedly found in this study more precisely.

Stress lowers the detection threshold for foul-smelling 2-mercaptoethanol.

Previous studies have reported enhanced vigilance for threat-related information in response to acute stress. While it is known that acute stress modulates sensory systems in humans, its impact on olfaction and the olfactory detection of potential threats is less clear. Two psychophysical experiments examined, if acute stress lowers the detection threshold for foul-smelling 2-mercaptoethanol. Participants in Experiment 1 (N = 30) and Experiment 2 (N = 32) were randomly allocated to a control group or a stress group. Participants in the stress group underwent a purely psychosocial stressor (public mental arithmetic) in Experiment 1 and a stressor that combined a physically demanding task with social-evaluative threat in Experiment 2 (socially evaluated cold-pressor test). In both experiments, olfactory detection thresholds were repeatedly assessed by means of dynamic dilution olfactometry. Each threshold measurement consisted of three trials conducted using an ascending method of limits. Participants in the stress groups showed the expected changes in heart rate, salivary cortisol, and mood measures in response to stress. About 20 min after the stressor, participants in the stress groups could detect 2-mercaptoethanol at a lower concentration than participants in the corresponding control groups. Our results show that acute stress lowers the detection threshold for a malodor.

Interindividual differences in chemosensory perception: Toward a better understanding of perceptual ratings during chemical exposures.

Perceptions that arise from stimulation of olfactory and trigeminal receptors in the nasal cavity guide the evaluation of chemical environment in humans. Strong interindividual differences in these assessments may be attributed to nonsensory factors such as gender, anxiety, and chemical sensitivity. Knowledge regarding the influence of these factors originates mainly from basic odor research using short-term exposure scenarios. In situations with continuous chemical exposures-common in the working environment-their impact is less clear. To investigate their role during the exposure to workplace chemicals, 4-hour experimental exposure studies (total N = 105) using nine different airborne chemicals were summarized. In each study, subjects evaluated a single chemical in a controlled environment by rating five chemosensory perceptions, including odor intensity, disgust, annoyance, pungency, and burning, several times during occupational limit and low exposures. It was investigated whether the effects of trait-like modulators, such as anxiety and self-reported chemical sensitivity, depend on exposure-related factors and gender. Trait-like modulators markedly affected ratings by women, but not men. Highly anxious women reported more intense annoyance and disgust than less anxious women. Stronger self-reported chemical sensitivity was associated with increased ratings of pungency and burning in women exposed to occupational limit concentrations. This study demonstrates that a complex interplay of exposure-related factors, gender, and trait-like individual differences affects perceptual ratings during continuous chemical exposure. It seems necessary to incorporate the assessment of specific as well as general trait-like modulators into future experimental exposure studies.

Multidimensional assessment of self-reported chemical intolerance and its impact on chemosensory effects during ammonia exposure.

PURPOSE: Healthy individuals differ in self-reported chemical intolerance (CI). It is unclear whether this inter-individual variability impacts well-being and performance in environmental and occupational settings with chemical exposures. So far, operational definitions and questionnaires of CI have either emphasized physical symptoms or affective/behavioral disruption. In contrast, this study focused on healthy individuals who reported strong CI which generalized to awareness, physiology, affect, and behavior. We investigated whether generalized self-reported CI is associated with hyper-reactivity and reduced cognitive functioning due to chemosensory-mediated distraction during ammonia exposure. METHODS: An online sample (N = 321) answered established CI questionnaires. Based on the convergent self-reports in these questionnaires, healthy women with generalized CI and healthy female control participants were selected (total N = 26). Baseline characterization was performed using implicit association, lung and olfactory function tests, health-related self-reports, plasma inflammatory and metabolic markers. Performance in neurobehavioral tasks, perceptual ratings, nasal inflammatory, neuroendocrine, and autonomic nervous system reactivity were examined by means of a 75-min whole-body challenge to ammonia (stepwise increase: 0-10 ppm). RESULTS: Correlational analyses confirmed the multidimensionality of CI. Participants with generalized self-reported CI exhibited better olfactory function and reported stronger pungency during the challenge than controls. Cognitive performance and physiological response to the challenge were comparable between the two groups. CONCLUSIONS: Self-reports of CI are complex and not easily assessed by unidimensional questionnaires. While generalized self-reported CI is associated with altered chemosensory processing, it seems unlikely that it modulates health effects and cognitive functioning during chemical exposure.

Low self-reported stress despite immune-physiological changes in paramedics during rescue operations.

Despite the high stress levels, paramedics seem to ignore or even negate the stress. This can be detrimental and lead to stress-related diseases. Therefore, we investigated the divergence between physiological and psychological stress responses of paramedics. Participants were 16 paramedics and 17 white-collar workers. We assessed psychological stress parameters, cortisol awakening response (CAR), and quantified immune parameters. In paramedics, electrocardiogram (ECG) was measured during one complete 24-hour shift. Our results revealed that CAR was higher in paramedics compared to controls. An alteration of immune parameters was observed even during days of free time. Also, ECG recordings showed acute stress in paramedics during rescue situations. Questionnaires revealed that rescue-service specific stressors affect psychological outcomes. However, paramedics reported significantly less mental stress and higher levels of depersonalization than controls. Taken together, our results suggest higher stress in paramedics compared to controls. However, paramedics negate their daily stress. Our findings underline therefore the importance to develop stress-management interventions for paramedics including sensitization for their stress reactions.

Spatiotemporal Processing of Bimodal Odor Lateralization in the Brain Using Electroencephalography Microstates and Source Localization.

The neuronal cascade related to the perception of either purely olfactory or trigeminal airborne chemicals has been investigated using electroencephalography (EEG) microstate analyses and source localization. However, most airborne chemicals are bimodal in nature, encompassing both properties. Moreover, there is an ongoing debate regarding whether there is one dominant nostril, and this could be investigated using these multichannel EEG methods. In this study, 18 right-handed, healthy participants (13 females) were monorhinally stimulated using an olfactometer with the bimodal component acetic acid during continuous EEG recording. Participants indicated the side of stimulation, the confidence in their decision, and rated the strength of the evoked perception. EEG microstate clustering determined four distinct maps and successive backfitting procedures, and source estimations revealed a network that evolved from visual-spatial processing areas to brain areas related to basic olfactory and trigeminal sensations (e.g., thalamus, cingulate cortex, insula, parahippocampal, and pre-/post-central gyri) and resulted in activation of areas involved in multisensory integration (e.g., frontal-temporal areas). Right-nostril stimulation was associated with faster microstate transition and longer involvement of the superior temporal gyrus, which was previously linked to chemical localization and provides evidence for a potential nostril dominance. The results describe for the first time the processing cascade of bimodal odor perception using microstate analyses and demonstrate its feasibility to further investigate potential nostril dominance.

Somatosensory Response to Trigeminal Stimulation: A Functional Near-Infrared Spectroscopy (fNIRS) Study.

Functional near-infrared spectroscopy (fNIRS) is an optical imaging technique measuring relative hemodynamic changes in superficial cortical structures. It has successfully been applied to detect a hemodynamic response in the somatosensory cortex evoked by irritating mechanical, electrical, and heat stimulations of limbs or the face. The aim of the current study was to explore the feasibility of fNIRS to detect respective responses evoked by irritating chemical stimulations of the nasal divisions of the trigeminal nerve. In two experiments, healthy subjects were exposed to acetic acid and ethyl acetate presented using a respiration-synchronized olfactometer. Results demonstrated that fNIRS can detect a signal in both hemispheres after birhinal (experiment 1: n = 14) and monorhinal (experiment 2: n = 12) stimulations using acetic acid but not ethyl acetate. This is a first evidence that fNIRS might be a suitable imaging technique to assess chemosensory neuronal correlates in the somatosensory cortex thereby offering a new, portable method to evaluate the irritating properties of certain volatiles in an objective, nonverbal, easy, and comparably inexpensive manner.

Concealed Around-the-Ear EEG Captures Cognitive Processing in a Visual Simon Task.

In theory, miniaturized systems such as the around-the-ear electrode arrays (cEEGrids) enable mobile monitoring of the electroencephalogram (EEG) in a variety of real life situations without interfering with the natural setting. However, the research benefit of such cEEGrid recordings critically depends on their validity. To investigate whether visual and motor processing are reflected in the cEEGrid-EEG, a direct comparison of EEG that was concurrently recorded with the cEEGrids and with a high-density cap setup was conducted. Thirteen participants performed a classic Simon task in which letters were presented laterally and a lateralized choice response was executed. N1, P1 and P300 event-related potential (ERP) waveforms were extracted from cEEGrid-EEG: they were found to be strongly correlated with corresponding waveforms extracted from cap-EEG but with lower signal strength and lower signal-to-noise-ratio (SNR). Event-related lateralizations (ERLs) recorded at posterior scalp sites were well reflected in middle cEEGrid pairs. Moreover, the effect size of the Simon correspondence effect on the extracted ERLs was similar between the two systems. However, lateralizations at central cap sites were less well reflected in the cEEGrid-EEG indicating a difficulty in capturing motor response preparation and execution. These results show that well-described visual and cognitive ERPs and ERLs can be measured using the cEEGrids, while motor-related cortical potentials are not well captured. This study further demonstrates the potential and possible limitations of unobtrusive cEEGrid-EEG recordings.

Does seasonal allergic rhinitis increase sensitivity to ammonia exposure?

Allergic inflammation in the upper airways represents a wide-spread health issue: Little is known about whether it increases sensitivity to airborne chemicals thereby challenging established exposure limits that neglect such differences in susceptibility. To investigate the role of pre-existing allergic inflammation, 19 subjects with seasonal allergic rhinitis (SAR) and 18 control subjects with low risk of sensitization were exposed for 4h to ammonia in two concentrations (cross-over design): 2.5ppm (odor threshold) and 0-40ppm (occupational exposure limit: 20ppm TWA). Prior to the whole-body exposure, it was confirmed that subjects with SAR showed persistent inflammation outside the pollen season as indicated by increased exhaled nitric oxide and total immunoglobulin E in serum compared to controls. Despite concentration-dependent increases in chemosensory perceptions and acute symptoms, SAR status did not modulate subjective effects of exposure. Moreover, SAR status did not affect the investigated physiological endpoints of sensory irritation: While eye-blink recordings confirmed weak ocular irritation properties of ammonia at 0-40ppm, this effect was not enhanced in SAR subjects compared to controls. Irrespective of SAR status, exposure to 0-40ppm ammonia did not result in a cortisol stress response, objective nasal obstruction as measured with anterior active rhinomanometry, or an inflammatory response as indexed by substance P, tumor-necrosis-factor α, and high-mobility-group protein 1 in nasal lavage fluid. At least for the malodorous compound ammonia, these results do not support the hypothesis that SAR enhances chemosensory effects in response to local irritants. Before generalizing this finding, more compounds as well as sensitization to perennial allergens need to be investigated.

Neurobehavioral effects of exposure to propionic acid revisited-Does psychosocial stress interfere with distractive effects in volunteers?

Local irritants stimulate the nervous system via chemosensory pathways that trigger cognitive distraction, subjective complaints about impaired health, and physiological defense reflexes (e.g. eye-blinks). At workplaces and in the environment chemical exposures often co-occur with psychosocial stress. This study investigated if stress modulates adverse effects of exposure to the local irritant and malodorant propionic acid (PA). Forty-eight participants were randomly assigned to an experimental (false negative feedback+salient surveillance) or control group. In a cross-over design, both groups were exposed for 4h to PA in concentrations of 0.3 and 0-20ppm (time-weighted average=10ppm). In the experimental group, the stress protocol induced moderate psychosocial stress as indicated by salivary cortisol and subjective responses. Despite concentration-dependent increases in chemosensory perceptions and symptoms, the level of exposure to PA had no impact upon the results of four out of six neurobehavioral tests. In the sustained attention test, there was a significant increase in error rates that corresponded to the exposure levels. However, a concentration-dependent impairment of spatial working memory and an adverse increase in eye-blink frequency were restricted to the control group. Stressed participants had shorter simple reaction times and high eye-blink frequency irrespective of exposure suggesting enhanced alertness. Psychosocial stress increased complaints, ocular irritation and unspecific symptoms at the end of the 0.3ppm exposure to a level that was comparable with that in the control group during exposure to 0-20ppm. Results indicate that the adverse effects of a local irritant and psychosocial stress are non-additive.