Central processing of acute muscle pain in chronic low back pain patients: an EEG mapping study

The presence of perceptual sensitization and related brain responses was examined in 14 chronic low back pain (CLBP) patients and 13 healthy controls comparable in age and sex. Multichannel EEG recordings and pain ratings were obtained during the presentation of 800 painful electrical intramuscular and intracutaneous stimuli each to the left m. erector spinae and the left m. extensor digitorum. Perception and pain thresholds were not significantly different between the two groups, though patients showed significantly more perceptual sensitization. Across all stimulation conditions, a larger EEG component 80 milliseconds after stimulation was observed in the CLBP group. No significant group differences were found for the N150. The component 260 milliseconds after stimulus onset was significantly smaller in the CLBP group. N80, N150, and perceptual sensitization were significantly positively correlated. These results indicate enhanced perceptual sensitization and enhanced processing of the sensory-discriminative aspect of pain, as expressed in the N80 component, in CLBP patients. This may be one neurophysiologic basis of sensitization and the chronicity process. The lower P260 component in the patients may be explained in terms of tonic pain inhibiting phasic pain or may be related to the affective distress observed in this patient group.