The Limbic System Modulations in Respiratory Somatosensation: Respiratory-Related Evoked Potentials and Magnitude Estimation

This study proposal is a continuation and expansion of the National Science Council project 99-2320-B-182-018 which is currently funded between Aug 2010 and July 2011. Human’s respiration cannot be sensed unless breathing is attended, occluded, or obstructed. Ventilatory status change results in cortical neuronal activation in the somatosensory cortex. This can be measured by the respiratory-related evoked potential (RREP) method with scalp surface electrodes. Different physiological or psychological states such as voluntary attention, background loads, and disease states can modulate cognitive awareness of breathing and the RREP. Respiratory sensory gating was demonstrated by the RREP with paired inspiratory occlusions. It was found that the second stimulus (S2) elicited smaller evoked potentials than the first stimulus (S1) in normal subjects. In normal controls the N1 peak S2/S1 ratio is on average less than 0.5. Respiratory sensory gating mechanism can be tested using different levels of intensities and frequencies of respiratory stimuli. Cognitive awareness of the obstructed breathing will then lead to subsequent decisions in behavioral responses. Further, the level of this cognitive awareness can be tested with individual’s estimated magnitude of respiratory loads. Little has been explored in the area of limbic systems in relation to respiratory perceptual gating as well as load magnitude estimation. However, previous research discovered that anxiety is often associated with distressing respiratory sensation and breathing effort. Also, negative emotions were related to higher respiratory complaints. The incidence of respiratory disease in people with anxiety disorders is much higher than in those without. It appears that the limbic systems may alter respiratory perception by changing respiratory drive or the interpretation of the loads. Our past study found that compared to nonsmokers, smokers after 12-hour nicotine withdrawal showed decreased respiratory sensory gating function (with the same level of respiratory occlusions). Also, compared to nonsmokers, smokers after the withdrawal reported higher anxiety levels. However it remains unclear how anxiety as a disease state can modulate respiratory sensation perceived at the cortical level, and whether spontaneous anxiety affects subjects’ estimation of their respiratory loads. The significance of this work lies in the fact that anxiety effects are fundamental to our understanding to respiratory perception. Our aim of this project is to systematically investigate the effect spontaneous anxiety on respiratory sensation. Firstly, we hypothesized that people with anxiety disorders will present a respiratory perceptual mechanism that is different from those without in RREP components. Secondly, we hypothesized that people with anxiety would show higher RREP N1 and P300 peak S2/S1 ratios (decreased respiratory sensory gating) than in control adults. Finally, we will examine and compare respiratory perception between high and low anxious individuals with magnitude estimation of respiratory loads. The fact that the preliminary results in our current ongoing study showed the same trend as our proposed study hypotheses suggests the feasibility of this proposed study. We expect the results of this project to serve as a basis for future respiratory perceptual studies in asthma, chronic obstructive pulmonary disease, and anxiety disorders.

Project ID:PC10007-1150
External Project ID:NSC100-2320-B182-018