Processing of pain- and body-related verbal material in chronic pain patients: central and peripheral correlates

The processing of pain-related, body-related and neutral words was assessed in chronic pain patients and matched healthy controls. During and after word presentation at perception threshold, electromyographic activity (EMG), heart rate, skin conductance level and electroencephalographic (EEG) data from 11 electrode sites were recorded. Startle responses were measured to suprathreshold word stimuli. Although the patients did not recognize more pain-related words, they produced an enhanced left-hemispheric N100 and N200 to pain-related as compared to neutral words. In addition, the patients did not show a distinct P300 but a continuous positive shift to all words extending into the 800-ms range. Skin conductance levels to the pain-related words were also enhanced in patients only. These data partially support the notion of pain-related implicit memory structures in the brain of chronic pain patients that may selectively draw attention to pain-related stimuli and may thus enhance pain perception.