The role of nicotine on respiratory sensory gating measured by respiratory-related evoked potentials

Effects of emotional contexts on respiratory attention task performance

Negative emotions have been found associated with high prevalence of respiratory disease and increased subjective feelings of dyspnea, while positive emotional stimulus has been suggested to alleviate dyspneic feelings. However, the extent to which different emotional contexts affect individuals' respiratory interoceptive attention was not clear. Therefore, the purpose of this study was to investigate the influences of emotional contexts on respiratory interoceptive accuracy, and the relationships between respiratory interoceptive accuracy and negative emotions as well as respiratory symptoms. Fifty-six healthy participants completed the self-reported questionnaires of depression, anxiety, and respiratory symptoms. During the experiment, the participants were instructed to watch one neutral and one positive affective picture series and mentally count the number of perceived occlusions (reported at the end of the trials). The Wilcoxon Signed-Rank test and Spearman's correlations were used to examine the effect of the emotional pictures and to explore the relationships between the level of emotional status or respiratory symptoms and respiratory interoceptive task performance. The significance level was set at p < 0.05. Our results did not show a significant difference in participants' occlusion counting task performance between the neutral and positive emotional context. However, Spearman's Rho correlation analysis revealed that depression level was negatively correlated with accuracy of the task performance in the neutral emotional context, and this relationship diminished in the positive emotional context. In summary, our study demonstrated that negative emotional status, especially depression, may lead to decreased respiratory interoceptive accuracy. Future studies are recommended to test the effect of positive emotional context on respiratory interoceptive task performance in individuals with clinical depression and anxiety.

The impact of emotional context on neural substrates of respiratory sensory gating

Psychological challenges have been found to impact respiratory symptom perception in healthy individuals as well as in patients with various neurological disorders. Human respiratory sensory gating is an objective measure to examine respiratory sensory information processing of repetitive respiratory mechanical stimuli in the central nervous system. With this electrophysiological method, patients with higher anxiety levels showed reduced respiratory sensory gating function in the cortex, and increased symptom perception. In addition, positive emotional contexts were found to increase the respiratory sensory gating function using RREPs. However, neural substrates related to emotional impacts on respiratory sensory gating remain still unclear. In the present study, we examined the emotion processing of respiratory sensory gating using functional magnetic resonance imaging. We hypothesized that positive compared with neutral stimuli would result in reduced brain activations in cortical areas with the paired occlusion paradigm. Thirty-five healthy adults participated in this event-designed fMRI experiment. Paired inspiratory occlusions (two transient occlusions with a 500 ms inter-stimulus-interval are delivered during one inspiration) were provided using an external trigger outside of the scanner. At least 40 paired inspiratory occlusions were collected for each trial. The experiment contained three runs during which participants underwent 12 min for the paired inspiratory occlusion paradigm while watching a fixation cross (the control condition), neutral and positive emotional picture series. The order of emotional picture series was randomized across the participants. Our results revealed an overall trend of reduction of brain activity from the neutral (minus fixation) condition, to the pleasant (minus fixation) condition. For bilateral thalamus and primary visual cortices, there was no significant difference in neural activation between the two contrasts of pleasant (Contrast_P–F) and neutral condition (Contrast_N–F). The activation of the mid-cingulate and the orbitofrontal cortex was lower in Contrast_P–F compared to Contrast_N–F. In conclusion, our results suggest that emotional context, especially positive valence, modulates neural correlates in middle cingulate cortex and orbitofrontal cortex in terms of respiratory sensory gating. Future studies are recommended to test emotional impacts on respiratory sensations in patients with neurological disorders.

Cortical Sources of Respiratory Mechanosensation, Laterality, and Emotion: An MEG Study

Airway obstruction activates mechanoreceptors that project to the cerebral cortices in humans, as evidenced by scalp encephalography recordings of cortical neuronal activation, i.e., respiratory-related evoked potential (RREP). However, neural evidence of both high spatial and temporal resolution of occlusion-elicited cortical activation in healthy individuals is lacking. In the present study, we tested our hypothesis that inspiratory mechanical stimuli elicit neural activation in cortical structures that can be recorded using magnetoencephalography (MEG). We further examined the relationship between depression and respiratory symptoms and hemispheric dominance in terms of emotional states. A total of 14 healthy nonsmoking participants completed a respiratory symptom questionnaire and a depression symptom questionnaire, followed by MEG and RREP recordings of inspiratory occlusion. Transient inspiratory occlusion of 300 ms was provided randomly every 2 to 4 breaths, and approximately 80 occlusions were collected in every study participant. Participants were required to press a button for detection when they sensed occlusion. Respiratory-related evoked fields (RREFs) and RREP peaks were identified in terms of latencies and amplitudes in the right and left hemispheres. The Wilcoxon signed-rank test was further used to examine differences in peak amplitudes between the right and left hemispheres. Our results showed that inspiratory occlusion elicited RREF M1 peaks between 80 and 100 ms after triggering. Corresponding neuromagnetic responses peaked in the sensorimotor cortex, insular cortex, lateral frontal cortex, and middle frontal cortex. Overall, the RREF M1 peak amplitude in the right insula was significantly higher than that in the left insula (p = 0.038). The RREP data also showed a trend of higher N1 peak amplitudes in the right hemisphere compared to the left (p = 0.064, one-tailed). Subgroup analysis revealed that the laterality index of sensorimotor cortex activation was significantly different between higher- and lower-depressed individuals (−0.33 vs. −0.02, respectively; p = 0.028). For subjective ratings, a significant relationship was found between an individual’s depression level and their respiratory symptoms (Spearman’s rho = 0.54, p = 0.028, one-tailed). In summary, our results demonstrated that the inspiratory occlusion paradigm is feasible to elicit an RREF M1 peak with MEG. Our imaging results showed that cortical neurons were activated in the sensorimotor, frontal, middle temporal, and insular cortices for the M1 peak. Respiratory occlusion elicited higher cortical neuronal activation in the right insula compared to the left, with a higher tendency for right laterality in the sensorimotor cortex for higher-depressed rather than lower-depressed individuals. Higher levels of depression were associated with higher levels of respiratory symptoms. Future research with a larger sample size is recommended to investigate the role of emotion and laterality in cerebral neural processing of respiratory sensation.

The impact of unpredictability of dyspnea offset on dyspnea perception, fear, and respiratory neural gating

Dyspnea is a debilitating and threatening symptom in various diseases. Affected patients often report the unpredictability of dyspnea episodes being particularly anxiety-provoking and amplifying the perception of dyspnea. Experimental studies testing dyspnea unpredictability together with related neural processes, physiological fear responses, and dyspnea-related personality traits are sparse. Therefore, we investigated the impact of unpredictability of dyspnea offset on dyspnea perception and fear ratings, respiratory neural gating and physiological fear indices, as well as the influence of interindividual differences in fear of suffocation (FoS). Forty healthy participants underwent a task manipulating the offset predictability of resistive load-induced dyspnea including one unloaded safety condition. Respiratory variables, self-reports of dyspnea intensity, dyspnea unpleasantness, and fear were recorded. Moreover, respiratory neural gating was measured in a paired inspiratory occlusion paradigm using electroencephalography, while electrodermal activity, startle eyeblink, and startle probe N100 were assessed as physiological fear indices. Participants reported higher dyspnea unpleasantness and fear when dyspnea offset was unpredictable compared to being predictable. Individuals with high levels of FoS showed the greatest increase in fear and overall higher levels of fear and physiological arousal across all conditions. Respiratory neural gating, startle eyeblink, and startle probe N100 showed general reductions during dyspnea conditions but no difference between unpredictable and predictable dyspnea conditions. Together, the current results suggest that the unpredictable offset of dyspnea amplifies dyspnea perception and fear, especially in individuals with high levels of FoS. These effects were unrelated to respiratory neural gating or physiological fear responses, requiring future studies on underlying mechanisms.

Cross-modal relationships of neural gating with the subjective perception of respiratory and somatosensory sensations

Neural gating is a phenomenon whereby the response to a stimulus in the electroencephalogram (EEG) is attenuated when preceded by an identical stimulus. Attenuation of paired auditory clicks has repeatedly been shown to be affected in mental disorders, for example, schizophrenia. Neural gating has also been measured for respiratory and somatosensory sensations, however the attenuation of bodily relevant stimuli has not yet been systematically related to the subjective perception of bodily sensations. This research direction is potentially relevant to explaining disease trajectories in psychosomatic conditions characterized by chronic breathlessness and/or pain. In the present study, we recorded high-density EEG from 85 healthy young adults while they experienced brief paired respiratory occlusions and brief paired electrocutaneous stimulation of the wrist. The event-related potential N1 was measured centro-laterally in response to the second relative to the first stimulus to quantify neural gating in both sensory domains. Participants experienced resistive loaded breaths and electrocutaneous stimuli of various intensities, rated their perceived intensity and unpleasantness, and performed magnitude estimation. Relationships of respiratory and somatosensory neural gating to the subjective intensity and unpleasantness of sensations, as well as the ability to discriminate sensations of varying intensities, were investigated intra-modally and cross-modally. We report significant relationships of the somatosensory neural gating to perceived intensity and unpleasantness of respiratory and somatosensory sensations, with the stronger neural gating relating to a stronger subjective intensity and unpleasantness. We discuss these unexpected findings through the lens of individual differences and different theoretical accounts on the origins of cortical attenuation of repetitive stimuli.

The effect of anxiety on brain activation patterns in response to inspiratory occlusions: an fMRI study

Respiratory sensations such as breathlessness are prevalent in many diseases and are amplified by increased levels of anxiety. Cortical activation in response to inspiratory occlusions in high- and low-anxious individuals was found different in previous studies using the respiratory-related evoked potential method. However, specific brain areas showed different activation patterns remained unknown in these studies. Therefore, the purpose of this study was to compare cortical and subcortical neural substrates of respiratory sensation in response to inspiratory mechanical occlusion stimuli between high- and low-anxious individuals using functional magnetic resonance imaging (fMRI). In addition, associations between brain activation patterns and levels of anxiety, and breathlessness were examined. Thirty-four (17 high- and 17 low-anxious) healthy non-smoking adults with normal lung function completed questionnaires on anxiety (State Trait Anxiety Inventory - State), and participated in a transient inspiratory occlusion fMRI experiment. The participants breathed with a customized face-mask while respiration was repeatedly interrupted by a transient inspiratory occlusion of 150-msec, delivered every 2 to 4 breaths. Breathlessness was assessed by self-report. At least 32 occluded breaths were collected for data analysis. The results showed that compared to the low-anxious group, the high-anxious individuals demonstrated significantly greater neural activations in the hippocampus, insula, and middle cingulate gyrus in response to inspiratory occlusions. Moreover, a significant relationship was found between anxiety levels and activations of the right inferior parietal gyrus, and the right precuneus. Additionally, breathlessness levels were significantly associated with activations of the bilateral thalamus, bilateral insula and bilateral cingulate gyrus. The above evidences support stronger recruitment of emotion-related cortical and subcortical brain areas in higher anxious individuals, and thus these areas play an important role in respiratory mechanosensation mediated by anxiety.

Alterations in oropharyngeal sensory evoked potentials (PSEP) with Parkinson's disease

Movement of a food bolus from the oral cavity into the oropharynx activates pharyngeal sensory mechanoreceptors. Using electroencephalography, somatosensory cortical-evoked potentials resulting from oropharyngeal mechanical stimulation (PSEP) have been studied in young healthy individuals. However, limited information is known about changes in processing of oropharyngeal afferent signals with Parkinson's disease (PD). To determine if sensory changes occurred with a mechanical stimulus (air-puff) to the oropharynx, two stimuli (S1-first; S2-s) were delivered 500ms apart. Seven healthy older adults (HOA; 3 male and 4 female; 72.2±6.9 years of age), and thirteen persons diagnosed with idiopathic Parkinson's disease (PD; 11 male and 2 female; 67.2±8.9 years of age) participated. Results demonstrated PSEP P1, N1, and P2 component peaks were identified in all participants, and the N2 peak was present in 17/20 participants. Additionally, the PD participants had a decreased N2 latency and gated the P1, P2, and N2 responses (S2/S1 under 0.6). Compared to the HOAs, the PD participants had greater evidence of gating the P1 and N2 component peaks. These results suggest that persons with PD experience changes in sensory processing of mechanical stimulation of the pharynx to a greater degree than age-matched controls. In conclusion, the altered processing of sensory feedback from the pharynx may contribute to disordered swallow in patients with PD.

Aerobic exercise training without weight loss reduces dyspnea on exertion in obese women

Dyspnea on exertion (DOE) is a common symptom in obesity. We investigated whether aerobic exercise training without weight loss could reduce DOE. Twenty-two otherwise healthy obese women participated in a 12-week supervised aerobic exercise training program, exercising 30 min/day at 70-80% heart rate reserve, 4 days/week. Subjects were grouped based on their Ratings of Perceived Breathlessness (RPB) during constant load 60 W cycling: +DOE (n=12, RPB≥4, 37±7 years, 34±4 kg/m(2)) and -DOE (n=10, RPB≤2, 32±6 years, 33±3 kg/m(2)). No significant differences between the groups in body composition, pulmonary function, or cardiorespiratory fitness were observed pre-training. Post-training,peak was improved significantly in both groups (+DOE: 12±7, -DOE: 14±8%). RPB was significantly decreased in the +DOE (4.7±1.0-2.5±1.0) and remained low in the -DOE group (1.2±0.6-1.3±1.0) (interaction p<0.001). The reduction in RPB was not significantly correlated with the improvement in cardiorespiratory fitness. Aerobic exercise training improved cardiorespiratory fitness and DOE and thus appears to be an effective treatment for DOE in obese women.

Respiratory sensory gating measured by respiratory-related evoked potentials in generalized anxiety disorder

The perception of respiratory sensations plays an important role both in respiratory diseases and in anxiety disorders. However, little is known about the neural processes underlying respiratory sensory perception, especially in patient groups. Therefore, the present study examined whether patients with generalized anxiety disorder (GAD) would demonstrate altered respiratory sensory gating compared to a healthy control group. Respiratory-related evoked potentials (RREP) were measured in a paired inspiratory occlusion paradigm presenting two brief occlusion stimuli (S1 and S2) within one inspiration. The results showed a significantly greater S2/S1 ratio for the N1 component of the RREP in the GAD group compared to the control group. Our findings suggest altered respiratory sensory processing in patients with GAD, which might contribute to altered perception of respiratory sensations in these patients.

Emotions and neural processing of respiratory sensations investigated with respiratory-related evoked potentials

OBJECTIVE

Patients with respiratory diseases such as asthma and chronic obstructive pulmonary disease frequently experience respiratory sensations, which are often perceived as unpleasant or threatening. However, the accurate perception of respiratory sensations is important for the management and treatment of these diseases. Emotions can substantially influence the perception of respiratory sensations and might affect the course of respiratory diseases, but the underlying neural mechanisms are poorly understood. The respiratory-related evoked potential (RREP) recorded from the electroencephalogram is a noninvasive technique that allowed first studies to examine the impact of emotions on the neural processing of respiratory sensations.

METHODS

In this review, we will briefly introduce the importance of the perception of respiratory sensations and the influence of emotions on respiratory perception. We then provide an overview on the technique of RREP and present a systematic review on recent findings using this technique in the context of emotions.

RESULTS AND CONCLUSIONS

The evidence currently available from studies in healthy individuals suggests that short-lasting emotional states and anxiety affect the later RREP components (N1, P2, P3) related to higher-order neural processing of respiratory sensations, but not the earlier RREP components (Nf, P1) related to first-order sensory processing. We conclude with a discussion of the implications of this work for future research that needs to focus on respiratory patient groups and the associated clinical outcomes.

The effect of anxiety on respiratory sensory gating measured by respiratory-related evoked potentials

Respiratory sensory gating is evidenced by decreased amplitudes of the respiratory-related evoked potentials (RREP) N1 peak for the second (S2) compared to the first occlusion (S1) when two paired occlusions are presented with a 500-millisecond (ms) inter-stimulus-interval during one inspiration. Because anxiety is prevalent in respiratory diseases and associated with altered respiratory perception, we tested whether anxiety can modulate individuals' respiratory neural gating mechanism. By using high-density EEG, RREPs were measured in a paired inspiratory occlusion paradigm in 11 low and 10 higher anxious individuals with normal lung function. The N1 peak gating S2/S1 ratio and the N1 S2 amplitudes were greater in higher compared to low anxious individuals (p's<0.05). In addition, higher anxiety levels were correlated with greater S2/S1 ratios (r=0.54, p<0.05) and S2 amplitudes (r=-0.49, p<0.05). The results demonstrate that anxiety is associated with reduced respiratory sensory gating which might underlie altered respiratory symptom perception in anxious individuals.

Tracheal occlusion conditioning in conscious rats modulates gene expression profile of medial thalamus

The thalamus may be the critical brain area involved in sensory gating and the relay of respiratory mechanical information to the cerebral cortex for the conscious awareness of breathing. We hypothesized that respiratory mechanical stimuli in the form of tracheal occlusions would modulate the gene expression profile of the thalamus. Specifically, it was reasoned that conditioning to the respiratory loading would induce a state change in the medial thalamus consistent with a change in sensory gating and the activation of molecular pathways associated with learning and memory. In addition, respiratory loading is stressful and thus should elicit changes in gene expressions related to stress, anxiety, and depression. Rats were instrumented with inflatable tracheal cuffs. Following surgical recovery, they underwent 10 days (5 days/week) of transient tracheal occlusion conditioning. On day 10, the animals were sacrificed and the brains removed. The medial thalamus was dissected and microarray analysis of gene expression performed. Tracheal obstruction conditioning modulated a total of 661 genes (p < 0.05, log₂ fold change ≥0.58), 250 genes were down-regulated and 411 up-regulated. There was a significant down-regulation of GAD1, GAD2 and HTR1A, HTR2A genes. CCK, PRKCG, mGluR4, and KCJN9 genes were significantly up-regulated. Some of these genes have been associated with anxiety and depression, while others have been shown to play a role in switching between tonic and burst firing modes in the thalamus and thus may be involved in gating of the respiratory stimuli. Furthermore, gene ontology and pathway analysis showed a significant modulation of learning and memory pathways. These results support the hypothesis that the medial thalamus is involved in the respiratory sensory neural pathway due to the state change of its gene expression profile following repeated tracheal occlusions.