To investigate the effects of homotopic and heterotopic conditioning pain modulation (CPM) on short-term cortical plasticity. Glutamate (tonic pain) or isotonic saline (sham) was injected in the upper trapezius (homotopic) and in the thenar (heterotopic) muscles. Intramuscular electrical stimulation was applied to the trapezius at pain threshold intensities, and somatosensory evoked potentials were recorded with 128 channel EEG. Pain ratings were obtained during glutamate and sham pain injection. Short-term cortical plasticity to electrical stimulation was investigated before, during, and after homotopic and heterotopic CPM versus control. Peak latencies at N100, P200, and P300 were extracted and the location/strength of corresponding dipole current sources and multiple dipoles were estimated. Homotopic CPM caused hypoalgesia (P = 0.032, 30.6% compared to baseline) to electrical stimulation. No cortical changes were found for homotopic CPM. A positive correlation at P200 between electrical pain threshold after tonic pain and the z coordinate after tonic pain (P = 0.032) was found for homotopic CPM. For heterotopic CPM, no significant hypoalgesia was found and a dipole shift of the P300 z coordinate (P = 0.001) was found between glutamate versus sham pain (P = 0.009). This generator was located in the cingulate. A positive correlation at P300 between pain ratings to glutamate injection and the x coordinate during tonic pain (P = 0.016) was found for heterotopic CPM. Heterotopic CPM caused short-term cortical plasticity within the cingulate that was correlated to subjective pain ratings. The degree of long-term depressive effect to homotopic CPM was correlated to the change in location of the P200 dipole.

The alpha rhythm (7.5–12 Hz) is one of the fundamental features of the human EEG which usually has maximum amplitude over occipital regions. It is well recognized that individuals have highly different magnitudes of alpha EEG. This study examined occipital alpha EEG activity during different levels of experimental tonic cuff-pressure pain. The aim was to study the pain reactions and pain–EEG relationship in subjects with high alpha (Hα) and low alpha (Lα) EEG. Tonic experimental cuff-pressure induced pain, and high density EEG (124 channels) were used. The pain-EEG responses for the high alpha (above 600 μV² in total alpha power at baseline), and low alpha (below 600 μV² in alpha power at baseline) subjects were analyzed. Forty healthy volunteers were included and received tonic pain for 3 min at three intensities (VRS2) intense, but no pain, (VRS4) slight pain, and (VRS6) moderate pain. There were no differences in stimulus intensities to reach the three ratings between the Hα and the Lα groups. The Hα and Lα groups are highly different in alpha1(PO3), alpha1(PO4), alpha1(PO7) and alpha1(PO8) EEG powers. A positive correlation (P = 0.008) between alpha2(PO3) EEG and average subjective pain ratings was specific for the Lα group. The Hα group showed alpha1 desynchronization as pain increased, but no significant correlation between alpha1 EEG powers and average subjective pain ratings. The differences between the Lα and the Hα in alpha EEG powers and the different pain-EEG responses may be related to different degrees of attention, fear of pain and pain related coping strategies.

AIMS:This study aimed to investigate the quality of the thermal grill illusion (TGI) and the importance of stimulus parameters (distance between, and number of stimulation bars). MATERIAL AND METHODS:Twenty-one different stimuli were applied to a group of 19 healthy subjects on the glabrous skin over the palm and fingers. RESULTS:The TGI was found to be painful (19.42% on the palm; 17.98% on the fingers), mechanical (25.24% on the palm; 5.62% on the fingers), emotional (13.59% on the palm; 14.61% on the fingers) or unusual (42.72% on the palm; 61.8% on the fingers) sensations. A total of 89.5% (palm) and 94.4% (fingers) of the subjects reported TGI. Between 45% (fingers) and 50% (palm) of the stimuli elicited TGI. Neither the distance (2 approximately 10 mm) between adjacent warm (40 +/- 1 degrees C) and cold (20 +/- 1 degrees C) bars nor the number of the stimulation bars (2 approximately 6) significantly affected the occurrence of the TGI (N.S.). The average reaction time was 2.4 +/- 0.1 seconds to the TGI sensation. Females showed longer reaction time than males (P <or= 0.001). CONCLUSION:The distance and number of stimulation bars were not important to the sensation of TGI, of which the responses varied. These results are useful for future TGI studies with respect to experimental design. The variability of the TGI needs to be considered in future experimental and clinical studies.

European Journal of PainVolume 13, Issue S1 p. S91a-S91 293 THE TIME COURSE OF THE THERMAL GRILL ILLUSION X. Li, X. Li Aalborg University, Aalborg E, DenmarkSearch for more papers by this authorL. Petrini, L. Petrini Aalborg University, Aalborg E, DenmarkSearch for more papers by this authorL. Wang, L. Wang Aalborg University, Aalborg E, DenmarkSearch for more papers by this authorL. Arendt-Nielsen, L. Arendt-Nielsen Aalborg University, Aalborg E, DenmarkSearch for more papers by this author X. Li, X. Li Aalborg University, Aalborg E, DenmarkSearch for more papers by this authorL. Petrini, L. Petrini Aalborg University, Aalborg E, DenmarkSearch for more papers by this authorL. Wang, L. Wang Aalborg University, Aalborg E, DenmarkSearch for more papers by this authorL. Arendt-Nielsen, L. Arendt-Nielsen Aalborg University, Aalborg E, DenmarkSearch for more papers by this author First published: 12 January 2012 https://doi.org/10.1016/S1090-3801(09)60296-2Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, IssueS1September 2009Pages S91a-S91 RelatedInformation

Reference is a very virtual issue in EEG and ERP. Understanding the difference of various references will make the applications more confident. In this work, somatosensory evoked potential (SEP) with stimulation on the right hand was studied. The SEP spatio-temporal analysis was conducted comparatively on six references, left mastoid (contralateral mastoid reference, CM), right mastoid (ipsilateral mastoid reference, IM), linked mastoids (LM), average reference (AR), vertex reference (Cz) and the infinity reference (IR) newly proposed in 2001. Among the six, CM is the one used in actual recordings, and the other five are obtained by off-line re-referencing. The comparison is conducted on four selected components (P30 ms, P40 ms, N90 ms and P230 ms) in both temporal and spatial aspects. The results show that references may have a distinct influence on the amplitudes of the scalp potentials, with relative error at some electrodes larger than 500%, and for some electrodes it may even change the polarity. Pair-wise multiple comparison (Tukey test) shows that the differences of peak values among various references are very significant (P<0.001) between Cz and IR\CM\IM\LM, and significant (P<0.01) between Cz and AR for component N90 ms; very significant (P<0.001) between Cz and IR\CM\IM\LM\AR, significant between IMLM and AR (P<0.01), CM and AR (P<0.05) for component P230 ms. The amplitude value order is CM/IM> or =LM>IR>AR>Cz. The two-ways (the six references vs. the four Peaks) repeated measures ANOVA test shows the effect of different references depends on various components; there is a statistically significant interaction between reference and the peak (P=<0.001). While for the spatial map of the potential amplitude, references will not affect the amplitude map shape if the color-bar is selected automatically, but if a fixed color-bar is chosen for data of various references, they may show some differences. These results mean a common reference is important for producing a comparable result between labs. As IR is theoretically a constant reference, we recommend it as the common choice in the future.

Objective: To study the effect of high-frequency (100 Hz) repetitive conditioning electrical stimulation (CES, 10min) on human somatosensory evoked potentials (SEPs) to evaluate if short-term cortical plasticity could be induced.Methods: Painful electrical stimulations were applied to thumb (D1) and little finger (D5) fingertips, respectively. The 124-channel EEG was recorded from 10 healthy male volunteers. Peak stages around 34, 45, 212, 331 ms were analyzed with focal maximum amplitude (FA) and area magnitude (AM) of scalp field potential, topography, and equivalent current dipole source localisation, comparing before and after two-level CES (high- vs. low-level) applied to the He-Gu acupoint.Results: After a high-level CES, the positive FA and AM of the current efflux showed a significant increase at the early phase 34 ms, and significantly decreased at 45 ms in D1 SEPs. The negative FA and AM of the current influx were significantly increased at late phase 350 ms of the D5 SEPs. Only 36 ms, the z-axis position of dipole was significantly changed from (x: -15.9 mm, y: 29.6 mm, z: 43.9 mm) to (x: -12.9 mm, y: 29.4 mm, z: 51.5 mm) for the D5 SEPs.Conclusions: The high-level CES significantly attenuated the subsequent cortical activation (45 ms peak for D I stimulation). Both low- and high-level CES significantly enhanced the late activities (226, 350 ms) in D5 stimulation. This may be explained by pain sensation change at the level of subcortical cingulate cortex induced by the site-dependent post-effect of CES.Significance: This study showed cortical plasticity induced by conditioning somatosensory stimulation. (c) 2006 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

This study determined: (a) if acupuncture stimulation at a traditional site might modulate ongoing EEG as compared with stimulation of a control site; (b) if high-frequency vs. low-frequency stimulation could exert differential effects of acupuncture; (c) if the observed effects of acupuncture were specific to certain EEG bands; and (d) if the acupuncture effect could be isolated at a specific scalp field, with its putative underlying intracranial source. Twelve healthy male volunteers (age range 22-35) participated in two experimental sessions separated by 1 week, which involved transcutaneous acupoint stimulation at selected acupoint (Li 4, HeGu) vs. a mock point at the fourth interosseous muscle area on the left hand in high (HF: 100 Hz) vs. low-frequency (LF: 2 Hz) stimulation by counter-balanced order. 124-ch EEG data were used to analyze the Delta, Theta, Alpha-1, Alpha-2, Beta, and Gamma bands. The absolute EEG powers (mu v(2)) at focal maxima across three stages (baseline, stimulation, post) were examined by two-way (condition, stage) repeated measures ANOVA. The activity of the Theta power significantly decreased (P = 0.02), compared with control during HF but not LF stimulation at acupoint stimulation, however, there was no study effect at the mock point. A decreased Theta EEG power was prominent at the frontal midline sites (FCz, Fz) and the contralateral right hemisphere front site (FCC2h). In contrast, the Theta power of low-frequency stimulation showed an increase from the baseline as those in both controlled mock point stimulations. The observed high-frequency acupoint stimulation effects of Theta EEG were only present during, but not after, simulation. The topographic Theta activity was tentatively identified to originate from the intracranial current source in cingulate cortex, likely ACC. It is likely that short-term cortical plasticity occurs during high-frequency but not low-frequency stimulation at the HeGu point, but not mock point. We suggest that HeGu acupuncture stimulation modulates limbic cingulum by a frequency modulation mode, which then may damp nociceptive processing in the brain. (c) 2005 Elsevier Inc. All rights reserved.

Based on EEG data recorded from 11 subjects with eyes open and the left mastoid (M) reference, three data sets were generated by re-referencing to the conventional linked mastoids (L), average (A) and the new 'infinity' (I) reference provided by the reference electrode standardization technique (REST, Yao 2001 Physiol. Meas. 22 693–711). The EEG power in the alpha frequency band with the four different references was calculated and compared with respect to the total energy and spatial amplitude weight centre (AWC) coordinates, to compare the effects of different references on power mapping in the frequency domain. Compared with the I reference, the AWCs of the EEG with the M reference show significant shifts to the right, frontal and superficial positions, the L reference significant shifts to frontal and superficial positions, and the A reference shifts the AWC significantly to a deeper position. Furthermore, the power maps of the M and L references have larger total power than the I reference, while that of the A reference has the smallest total power. These results confirm that different choices of reference electrodes result in systematic changes in the distribution of EEG frequency power, and in order to reduce the effect of such systematic shifts on the explanation of EEG mappings, a common reference is necessary for EEG research. We recommend the I reference for objective use in cross-laboratory studies and clinical practices, as it is far from all the other electrodes and can act as a neutral reference.