Mechanism of Respiratory Sensation---Effects of the Limbic System

Cortical neuronal activation in the somatosensory cortex by respiratory stimuli can be measured by scalp surface electrodes in humans. The averaged signal was defined as the respiratory-related evoked potential (RREP). The fact that eupnic breathing is usually not sensed suggests the existence of a “gate” between the brainstem and the cortices. Respiratory sensory gating mechanism can be tested using different levels of intensities and frequencies of respiratory stimuli. Different physiological or psychological states such as voluntary attention, background loads, and disease state 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 second stimulus (S2) elicited smaller evoked potentials than the first stimulus (S1). In normal controls the N1 peak S2/S1 ratio is on average less than 0.5. This gating mechanism in the central nervous system (CNS) is important for humans to judge and make decisions on subsequent behavioral responses. Using auditory and somatosensory modalities, it has been demonstrated that emotional state or anxiety can significantly affect gating functions in the CNS. The inability to gate out redundant visual or auditory stimuli under anxious state results in “sensory flooding”. This may be associated with patients’ visual or auditory hallucination. Little has been explored in the area of limbic systems in relation to respiratory perceptual gating. However, previous research discovered that anxiety is often associated with distressing respiratory sensation and breathing effort. Also, negative emotions were related to increased 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 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 affect and anxiety can modulate respiratory sensation perceived at the cortical level. The significance of this work lies in the fact that emotional and anxiety effects are fundamental to our understanding of respiratory perception. Our aim of this project is to investigate the effect of experimentally induced affective change or spontaneous anxiety on respiratory sensation. We hypothesized that induced negative affect will result in decreased respiratory sensory gating function represented by the RREP N1 and P300 peak amplitudes (higher S2/S1 ratios) and create sensory flooding phenomena. Accordingly, people with anxiety disorders will present a respiratory perceptual mechanism that is different from those without in RREP components. Finally, people with anxiety would show higher S2/S1 ratios (decreased respiratory sensory gating) than that in control adults. Our preliminary study showed that in healthy adults, high anxious individuals have lower respiratory sensory gating function than low anxious individuals, and therefore suggested 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:PC9909-0196
External Project ID:NSC99-2320-B182-018