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Neurophysiological correlates of the placebo effect in nausea
Neurophysiological correlates of the placebo effect in nausea
Background: Evidence indicates that nausea can be modulated by placebo interventions, however, little is known about the underlying cognitive mechanisms. Therefore, the present study examined behavioral and electroencephalography (EEG) correlates of the placebo effect on nausea. Methods: On two consecutive days, 90 healthy subjects (45 females) were exposed to a nauseating visual stimulus for 20 minutes. Nausea was continuously rated on a numeric rating scale (a ‘10’-point NRS, with ‘0’ indicating no nausea and ‘10’ maximal tolerable nausea). Day 1 served as a control condition. Placebo intervention occurred during day 2. Subjects were split into two groups: the placebo group received sham acupuncture (coupled with expectancy manipulation of nausea improvement), whereas subjects in the control group did not receive any treatment. Thirty-two channels of EEG were recorded during baseline and nausea exposure on both days as well as during the placebo intervention on day 2. Fast Fourier transformation (FFT) at central electrodes C3 and C4 and exact low resolution electromagnetic tomography (eLORETA) were used to examine EEG correlates of the placebo effect in nausea. Results: On the first day, both sexes showed severe nausea (NRS ≥ 5) in response to the nauseating stimulus. The nausea response was associated with elevated delta power (0.5-4 Hz) in the FFT spectrum. Additionally, source-level analyses revealed nausea related changes in the limbic, parietal, occipital, and frontal lobe, as well as in the insula. On day 2, both sexes showed reduced expectation of nausea following expectancy manipulation and sham acupuncture point stimulation on the NRS, indexed by changes in frontal lobe and anterior cingulate activity. In line with the main hypothesis in this study, both sexes showed a placebo effect on nausea, indexed by reduced nausea on the NRS. Among females, the placebo effect was accompanied by reduced delta power in the FFT spectrum, decreased placebo related activation in parietal, frontal, and temporal lobe as well as reduced stress levels. In contrast, the placebo effect on nausea in males displayed increased activation in the limbic, sub-lobar, and occipital lobe. Conclusion: Results emphasize the effectiveness of sham acupuncture in nausea and allow first insights into underlying central mechanisms in females and males. In particular, the positive expectation of nausea improvement following expectancy manipulation and sham acupuncture seems to be similarly modulated in females and males, specifically via frontal structures. On the other hand, the placebo effect on nausea alone may be differentially modified in females and males in the central nervous system.
placebo effect, nausea, stress, motivation, electroencephalography
Haile, Anja
2018
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Haile, Anja (2018): Neurophysiological correlates of the placebo effect in nausea. Dissertation, LMU München: Faculty of Medicine
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Abstract

Background: Evidence indicates that nausea can be modulated by placebo interventions, however, little is known about the underlying cognitive mechanisms. Therefore, the present study examined behavioral and electroencephalography (EEG) correlates of the placebo effect on nausea. Methods: On two consecutive days, 90 healthy subjects (45 females) were exposed to a nauseating visual stimulus for 20 minutes. Nausea was continuously rated on a numeric rating scale (a ‘10’-point NRS, with ‘0’ indicating no nausea and ‘10’ maximal tolerable nausea). Day 1 served as a control condition. Placebo intervention occurred during day 2. Subjects were split into two groups: the placebo group received sham acupuncture (coupled with expectancy manipulation of nausea improvement), whereas subjects in the control group did not receive any treatment. Thirty-two channels of EEG were recorded during baseline and nausea exposure on both days as well as during the placebo intervention on day 2. Fast Fourier transformation (FFT) at central electrodes C3 and C4 and exact low resolution electromagnetic tomography (eLORETA) were used to examine EEG correlates of the placebo effect in nausea. Results: On the first day, both sexes showed severe nausea (NRS ≥ 5) in response to the nauseating stimulus. The nausea response was associated with elevated delta power (0.5-4 Hz) in the FFT spectrum. Additionally, source-level analyses revealed nausea related changes in the limbic, parietal, occipital, and frontal lobe, as well as in the insula. On day 2, both sexes showed reduced expectation of nausea following expectancy manipulation and sham acupuncture point stimulation on the NRS, indexed by changes in frontal lobe and anterior cingulate activity. In line with the main hypothesis in this study, both sexes showed a placebo effect on nausea, indexed by reduced nausea on the NRS. Among females, the placebo effect was accompanied by reduced delta power in the FFT spectrum, decreased placebo related activation in parietal, frontal, and temporal lobe as well as reduced stress levels. In contrast, the placebo effect on nausea in males displayed increased activation in the limbic, sub-lobar, and occipital lobe. Conclusion: Results emphasize the effectiveness of sham acupuncture in nausea and allow first insights into underlying central mechanisms in females and males. In particular, the positive expectation of nausea improvement following expectancy manipulation and sham acupuncture seems to be similarly modulated in females and males, specifically via frontal structures. On the other hand, the placebo effect on nausea alone may be differentially modified in females and males in the central nervous system.