Changes of Spontaneous Oscillatory Activity to Tonic Heat Pain

Abstract

Transient painful stimuli could induce suppression of alpha oscillatory activities and enhancement of gamma oscillatory activities that also could be greatly modulated by attention. Here, we attempted to characterize changes in cortical activities during tonic heat pain perception and investigated the influence of directed/distracted attention on these responses. We collected 5-minute long continuous Electroencephalography (EEG) data from 38 healthy volunteers during four conditions presented in a counterbalanced order: (A) resting condition; (B) innoxious-distracted condition; (C) noxious-distracted condition; (D) noxious-attended condition. The effects of tonic heat pain stimulation and selective attention on oscillatory activities were investigated by comparing the EEG power spectra among the four experimental conditions and assessing the relationship between spectral power difference and subjective pain intensity. The change of oscillatory activities in condition D was characterized by stable and persistent decrease of alpha oscillation power over contralateral-central electrodes and widespread increase of gamma oscillation power, which were even significantly correlated with subjective pain intensity. Since EEG responses in the alpha and gamma frequency band were affected by attention in different manners, they are likely related to different aspects of the multidimensional sensory experience of pain. The observed contralateral-central alpha suppression (conditions D vs. B and D vs. C) may reflect primarily a top-down cognitive process such as attention, while the widespread gamma enhancement (conditions D vs. A) may partly reflect tonic pain processing, representing the summary effects of bottom-up stimulus-related and top-down subject-driven cognitive processes.

Subjective pain perception mediated by alpha rhythms

“…The attention modulation of pain related alpha activity was also observed in tonic 7 pain studies (Peng et al, 2014). With the delivery of 5-min tonic heat painful stimuli, 8 the effect of selective attention was characterized as a significant and consistent 9 decrease of spontaneous alpha oscillatory activity over somatosensory areas 10 contralateral to the stimulated side, by comparing the alpha activity in 11 nociceptive-attended (rating the stimulus intensity at the end of each minute) and (Liu et al, 2011a;Liu et al, 8 2011b).…”

“…It is quite likely that attention 19 exerts its effect on pain perception through modulating the coherence of ongoing 20 oscillations selectively for the neurons involved in encoding attended stimuli. 21 22 Therefore, the attention modulation of pain (i.e., clear influences on the sensory and 23 affective dimensions of pain experience) could be mediated by changes of alpha 24 oscillatory activities (Foxe and Snyder, 2011;Hauck et al, 2007;Hu et al, 2013;May 25 et al, 2012;Ohara et al, 2004;Peng et al, 2014). The intensified alpha suppression 26 within pain-related brain areas (e.g., somatosensory cortex) due to attention directed 27 to pain, is quite likely reflecting attentional augmentation of painful information 28…”

“…Instead, the alpha response mediating 8 attention modulation of pain should be identified by comparison of alpha responses 9 in different experimental conditions, e.g., the difference of alpha response in 10 pain-attended and pain-distracted conditions. 11 12 Current studies investigated attention modulations of pain mostly assessed the alpha 13 activities within a wide range of alpha frequency bands (May et al, 2012;Ohara et al, 14 2004;Peng et al, 2014), e.g., 7-14 Hz. However, with more and more evidence 15…”

Moving Toward Conscious Pain Processing Detection in Chronic Disorders of Consciousness: Anterior Cingulate Cortex Neuromodulation

“…2,5,48 Although our data show a link between the ACCinduced output and the centroparietal gBO (given the clinical-electrophysiological correlations), the fact that this correspondence could be a marker of ongoing consciousness generation and maintenance, requiring multiple and integrated brain activations, 22,23 is debatable. Although it has been shown that gBO in the centroparietal region could be related to pain processing, regardless of the stimulus repetition or the attention level, 36,42,66,91 and that it may have a key role in the sensorimotor transformation of pain (given the correlation with reaction time speediness in animal and human experimental models), 40,90 the pain-induced gBO may also be related to automatic attention-related pain processing. 82 Nonetheless, a correlation between activation of the ACC and the pain-control parietal networks has been shown previously.…”

“…In healthy individuals, cortical pain processing mechanisms (depending on wide frontoparietal networks) 12 can be studied through analysis of nociceptive-induced g-band oscillatory activity (gBO) within centroparietal areas, without any substantial need for the individual's participation or cognitive/ motor output. 36,66 Nociceptive-induced gBO may represent a marker of conscious and subjective pain perception, the access of the neural process regarding nociceptive and salient stimuli to a higher conscious level, or the summary effects of bottom-up and topdown processes concerning pain modulation. 77,81 Within the wide frontoparietal network, the anterior cingulate cortex (ACC) could have a striking role in pain processing and gating at the cortical level.…”