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

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

Sniffin’ Sticks and Olfactometer-Based Odor Thresholds for n-Butanol: Correspondence and Validity for Indoor Air Scenarios

Threshold assessments for the reference odorant n-butanol are an integral part of various research, clinical, and environmental sensory testing procedures. However, the practical significance of a high or low threshold for n-butanol beyond a particular testing environment and procedure are often unclear. Therefore, this study aimed to determine between-method correlations and to investigate the association between the n-butanol threshold and perceptual/behavioral odor effects in natural breathing scenarios in 35 healthy adults. The thresholds for n-butanol derived from the Sniffin’ Sticks test and determined by the ascending limit dynamic dilution olfactometry procedure were significantly correlated (∣r∣ = 0.47). However, only the thresholds determined by olfactometry were significantly correlated to the odor detection of n-butanol in an exposure lab. Moreover, participants with a higher sensitivity for n-butanol in the olfactometer-based assessment rated ammonia, during a 75 min exposure, to be more unpleasant and showed better performance in a simultaneous 3-back task than participants with lower sensitivity. The results of this study suggest that beyond the strict parameters of a certain psychophysical procedure, the threshold for n-butanol can be a meaningful indicator of odor detection and effects in some cases

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

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

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