Linear and nonlinear analyses of EEG dynamics during non-painful somatosensory processing in chronic pain patients

Abstract

The aim of our study was to characterize brain dynamics of affective modulation of somatosensory processing in chronic pain. We hypothesized that chronic pain patients will show abnormal EEG activity under negative mood conditions compared to healthly controls. Nineteen patients with chronic pain and 21 healthy subjects participated in the experiment. Multiscale entropy, fractal dimension, event-related potentials, and fast Fourier trasnform were used to analyze EEG data. A significant enhancement of entropy was found in pain patients were viewing unpleasant pictures. By contrast, no signifiant differences due to hemisphere or affective condition were found on nonlinear measures for healthy controls. Analyses of somatosensory ERPs showed that P50 amplitudes elicited by pleasant pictures were more reduced in chronic pain patients than in healthy controls. Finally, we observed that EEG band power was lower in pain patients than in healthy controls, in particular for theta and beata bands over sensorimotor cortices and temporal regions when viewing pleasant images. These findings suggest that sustained pain seems to be accompanied by an abnormal activation and dynamic of brain netwoork related to emotional processing os somatosensory information in chronic pain. Furthermore, our findings suggest that both linear and nonlinear measures of EEG time series may contribute to the understandings of brain dysfunction in chronic pain.