Respiratory sensory gating indices of inspiratory mechanical stimulus elicited cortical neural activation in humans

• Main Author: Chan, Pei-Ying Sarah
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01.01.2008
• Subjects: Veterinary services
• ISBN: 9781109024487; 1109024487

Cortical neuronal activation, measured by the respiratory related evoked potentials, can be elicited by inspiratory occlusions. However, cognitive awareness of breathing is usually not sensed unless ventilation is changed. This suggests that respiratory stimuli are filtered in and out of cognitive brain centers. Somatosensory gating was evidenced by decreased amplitudes of the N100 peak for the second stimulus (S2) when S2 was presented after a 500-millisecond (msec) interval after the first stimulus (S1). The purposes of the present thesis included demonstrating a neural respiratory gating system using inspiratory occlusions, investigating the relationship between somatosensory cortical activation and respiratory somatosensation, and exploring the parameters that modulate respiratory sensory gating. Study 1 examined the respiratory sensory gating using a paired inspiratory occlusion paradigm. The RREP were recorded from 20 healthy adults free of respiratory, neurological, or cardiovascular diseases. Twenty healthy subjects completed the paired inspiratory occlusion (RREP) trial. Thirteen of the subjects also completed the paired mouth air puffs (MEP) trial, and the paired hand air puffs (SEP) trial. All paired presentations lasted for approximately 150 msec each and were separated by 500 msec. The results demonstrated that the paired inspiratory obstruction paradigm with 500 msec inter-stimulus interval (ISI) elicits a reduced S2 response. The RREP N1 S2/S1 ratio, MEP and SEP N100 S2/S1 ratios were less than 0.5. These results were consistent with central neural gating of respiratory, mouth, and somatosensory afferent input. Study 2 assessed the effect of attention on respiratory and mouth mechano-sensory gating. The RREP were recorded in 23 healthy subjects with the paired occlusion paradigm. The mouth air puff EP (MEP+) were recorded in 12 healthy adults and the negative mouth pressure EP (MEP-) were recorded in 11 healthy adults. All protocols were recorded in ignore and attend trials. The results demonstrated that respiratory gating was evident for the N1 and P300 peaks under both attend and ignore conditions. The RREP P300 S2/S1 ratios were significantly smaller in attend than the ignore condition, indicating an effect of controlled attention producing a greater gating out of the cognitive activity for the second stimulus. Study 3 investigated the effect of nicotine withdrawal as well as acute nicotine administration on respiratory sensory gating. The RREP were recorded in 16 smokers with 12-hour withdrawal from nicotine and 17 non-smokers using the paired occlusion protocol. Self-rated anxiety level was assessed by the state-trait anxiety inventory (STAI) questionnaire to the subject prior to every RREP trial. In smokers, the RREP were initially measured after nicotine withdrawal, then they were provided with either nicotine or placebo gum followed by the second RREP trial. Non-smokers received only placebo gum. The results demonstrate that respiratory sensory gating was decreased in smokers, compared to nonsmokers, after 12 hours of nicotine withdrawal. However, no difference was found in self-rated state anxiety level between smokers and nonsmokers after the withdrawal. Nicotine increased respiratory sensory gating in smokers to a S2/S1 ratio similar to non-smokers. Respiratory sensory gating in non-smokers was not affected, but decreased in smokers, with the administration of the placebo gum.