EPV 25. Gamma-oscillations as a clinical marker of pain perception - a promising approach?

Abstract

Background Numerous studies have used ERP-waveforms of the EEG both with nociceptive as well as tactile stimuli to answer research questions or as a functional marker of the sensory system to clinically test the integrity of signaling pathways. Recent studies brought forward the idea that gamma-band-oscillations (GBOs) between 35 and 100 Hz may play an important role in conscious perception and could be a specific marker for the perception of pain. In this study, we aimed to test whether GBOs can be reliably induced, whether they code stimulus intensity, and whether they are specific for nociceptive stimuli compared to tactile, non-nociceptive stimuli. Methods A 17-channel EEG was recorded in 12 healthy volunteers (6 famales, 6 males) with 1 kHz continous sampling. In different blocks of 90 stimuli each, nociceptive laser stimuli of three different intensities (one intensity at pain threshold, two intensities above) and pneumatic tactile stimuli at two intensities (supra threshold; 2 and 4 bars; not painful) were delivered to the right hand and foot including one repetition, resulting in 180 stimuli per location and modality. Data were segmented into epochs of 3 s (1 sec pre stimulus interval), and subjected to a wavelet-based time frequency analysis (Letswave 5 by A. Mouraux, Brussels) in two separate analyses for the frequency ranges of 1–30 Hz and 30–100 Hz. Results Our results indicate that there is high variability between subjects with respect to occurence and signal strength of the gamma response. Averaged across subjects, a significant increase in gamma during the first 500 ms following the stimulus was observed for nociceptive stimuli only in a frequency range between 40 and 70 Hz in close temporal relation with the evoked EEG-response in the time domain. Both, the gamma and the evoked responses increased with stimulus intensity. A clear contralateral topography restricted to the scalp area overlaying the primary somatosensory cortex was not confirmed. Conclusions The difference in the appearance of GBOs between laser (painful) and pneumatic (tactile) stimuli could mean this response might be specific for the perception of pain. Whether higher salience of the nociceptive stimulus plays a critical role cannot be excluded. These results may help to get a better objective understanding of the perception of pain. Given the variability of individual responses, a clinical application would currently not warrant unambiguous results, but GBOs could be a promising marker in the future. Supported by Deutsche Forschungsgemeinschaft DFG SFB1158 (B05).