Research reportPre-stimulus alpha power affects vertex N2–P2 potentials evoked by noxious stimuli
Introduction
Several lines of evidence have found relationships between electroencephalographic (EEG) oscillations preceding nonpainful auditory or visual stimuli and the amplitude of averaged event-related potentials (ERPs) or evoked potentials (EPs) [11], [12], [15], [17], [37], [50], [51], [69], [70]. Pre-stimulus EEG oscillations at alpha band (about 10 Hz) would especially affect the amplitude of EPs or ERPs. Some studies have shown that lower the pre-stimulus alpha power, higher the amplitude of the ERPs or EPs [20], [27], [30], [64], [66]. The same was true for theta power (about 4–7 Hz) and EPs [13], [14], [16], [77]. Noteworthy, this kind of relationship does not held when the external stimulus is associated with specific attention demands. It has been shown a positive correlation between pre-stimulus alpha power and amplitude of N1 and P3 (N, negative; P, positive) components of the ERPs associated with the conscious perception of an infrequent stimulus (e.g., see ref. [36]).
The important relationship between the amplitude of pre-stimulus alpha oscillations and the amplitude of EPs is not surprising. Alpha oscillations dominate EEG activity in subjects at rest and reflect features of brain state that are important in relation to the subsequent cortical information processing. Alpha rhythms are strictly related to attentional level and cortical information processing in that enhancement or increase of alpha power reflects elaboration or inhibition of sensory stimuli [56], [63]. These oscillations usually range from 6 to 12 Hz and have been associated with different functional meanings as a function of frequency sub-band [18], [25], [55]. The amplitude of slow-frequency (8–10 Hz) alpha oscillations was related to attentional focus, whereas the amplitude of fast-frequency (10–12 Hz) alpha oscillations was related to cognitive resource allocation on specific sensory modalities [19], [32], [33], [41], [42], [46], [47], [48], [49], [73]. In general, lower is the amplitude of alpha rhythms, better is the information transfer (“gating”) through sensorimotor thalamo-cortical and cortico-cortical pathways [43], [63].
It can be hypothesized that the amplitude of pre-stimulus alpha oscillations, as a reflection of the functional state of thalamo-cortical and cortico-cortical channels, affects not only the cortical processing of nonpainful auditory and visual stimuli (as reported by the quoted papers of the first paragraph) but also the cortical processing of noxious stimuli. This issue is of extreme importance from the comparative evaluation of physiological substrate of painful versus nonpainful information processing and its possible clinical implication (i.e. neurophysiological concomitants of chronic pain). The present EEG study tested the hypothesis that the power of pre-stimulus alpha oscillations affects the cortical processing of sharp and localizable noxious stimuli as revealed by the amplitude of vertex N2–P2 complex evoked by laser stimulation, which has been frequently employed in previous experimental and clinical studies [3], [23]. With proper stimulation parameters, noxious laser stimuli mainly activate nociceptive A-delta and are experienced as sharp, localizable, and scalable; whereas, the use of different stimulation parameters activate C-fibers and induce a dull, hardly localizable pain [2], [21], [22], [80], [82], [84], [85], [86].
Section snippets
Subjects
Ten healthy voluntary subjects (five males, mean age = 24 years, range: 20–32 years) were recruited for the present experiments. A preliminary clinical interview ascertained that none of the subjects had an history of psychiatric or neurological diseases or made recent use of psychoactive drugs. All subjects signed a written informed consent according to the Declaration of Helsinki; they could freely interrupt the investigation at any time. The local Institutional Ethics Committee approved the
Spatio-temporal evolution of Laplacian LEPs
Fig. 2a plots grand average waveforms of the Laplacian LEPs computed at representative electrodes (C3, Cz) for the two sub-groups of EEG single trials (high- and low-band power). These waveforms were calculated at alpha 1, alpha 2 and alpha 3 sub-bands. Furthermore, mean latency of the N2–P2 complex for each alpha band and sub-group of EEG single trials is reported in Table 1. In general, the N2–P2 complex of the LEPs showed standard shape and mean latency. The N2 and P2 peaked at about 160 and
Discussion
Results of the present LEPs study showed clear differences in amplitude of the vertex N2–P2 potentials evoked by noxious stimulation as a function of the power of fast-frequency (about 10–12 Hz) band alpha power. Compared to the EEG single trials with pre-stimulus high 10–12 Hz power, those with low 10–12 Hz power were associated with greater amplitude of the vertex N2–P2 complex of the LEPs. LORETA analysis estimated the main source of this difference in supplementary motor and cingulate areas,
Conflict of interest
All authors had not any actual or potential conflicts of interest including any financial, personal or other relationships with other people or organizations.
All co-authors authorized the submission of the enclosed manuscript. The manuscript has not been published or is not under consideration for publication elsewhere. All ethical statements of your journal fit with the ethical procedures followed by the present study.
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2015, NeuropsychologiaCitation Excerpt :The lack of relationship between two error patterns in error trials suggests the independence of these two neural mechanisms. Some previous studies have reported the modulation effect of pre-stimulus brain activities on following ERPs evoked by visual, auditory or tactile stimuli (Babiloni et al., 2008; Boly et al., 2007; Brandt and Jansen 1991; Lee et al., 2011). Specifically, pre-stimulus alpha power has been noticed to modulate visual N1/P2 components (Brandt and Jansen 1991), auditory oddball N1/N2 (Lee et al., 2011), and N2-P2 complex (Babiloni et al., 2008), in a homogeneous activation relationship, i.e., high alpha power associated with low amplitudes of ERPs.
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2015, Biological PsychologyCitation Excerpt :If the alterations of alpha activity really exist in some chronic pain situations, we may even modulate patients’ levels of alpha activity using neuro-feedback, to relieve pain perception. (4) The association between modulations of alpha activities and behavioral performance was shown in previous studies (Babiloni et al., 2008; Brandt, Jansen, & Carbonari, 1991; Lange, Halacz, van Dijk, Kahlbrock, & Schnitzler, 2012; Linkenkaer-Hansen, Nikulin, Palva, Ilmoniemi, & Palva, 2004; Rahn & Basar, 1993a, b; Zhang & Ding, 2010). With the application of neuro-stimulation techniques outside the skull, such as Transcranial Magnetic Stimulation (TMS), it is possible to selectively modulate brain oscillatory activity.
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2013, Clinical NeurophysiologyCaffeine enhances frontal relative negativity of slow brain potentials in a task-free experimental setup
2010, Brain Research BulletinCitation Excerpt :Although our experimental design was such that it would be difficult to expect any substantial resting state, pre-stimulus variability in the brain states between caffeine and placebo conditions, this putative invariance was not directly tested as reflected in the above statistical analysis. It is well known that pre-stimulus alpha power differences are a rigorous predictor of the post-stimulus behavioral and ERP effects [1,12,20,26,42,43]. Therefore, we also carried out an additional analysis of the possible relation between pre-stimulus alpha power levels and our principal effects.