Chapter 6 – EEG imaging 213 that has also been implicated in nocebo hyperalgesia 47,50,51. Our finding of increased complexity of gamma-band oscillations in those more susceptible to nocebo hyperalgesia may thus provide electrophysiological evidence of specific underlying cognitive-emotional processes, such as associative learning ability as well as fear processing. Alpha band oscillatory power has been shown to underlie the perceptual processing of incoming stimuli, including sensory perception 52. Our study was methodologically different from the two previous studies on electrophysiological nocebo correlates 15,18 and our results do not show consistent support of previous findings relating alpha oscillations to nocebo hyperalgesia. While our findings indicate an involvement of alpha band oscillations during acquisition, we did not find pre- to postacquisition changes in alpha oscillations. Methodologically, it possible that the time elapsed between the first and second resting state recordings was too long, resulting in a failure to capture electrophysiological changes in alpha oscillations related to nocebo processing. Nevertheless, we found that nocebo trials during the acquisition phase were characterized by decreased power in the alpha band, as compared to control trials. Our finding may reflect the formation of pain expectations and an inhibitory function of alpha oscillations in pain perception. Moreover, alpha-band oscillations where involved when comparing the experience of baseline high-pain stimulations to the experience of increased pain under nocebo hyperalgesic conditions, in the evocation phase. We found that there was a significant increase in alpha-band power during nocebo responses, compared to baseline pain of a matched, high intensity pain stimulus. In line with the literature, these findings may reflect the role of alpha-band oscillations in expectations 8,9, and the cognitive regulation of pain 10,11.
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