| Focused attention on the objective aspects of pain was found to be effective for pain down-modulation pain among chronic pain people who tend to have pain hypervigilance. This study aimed to investigate the neural processes associated with focused attention through imagery of sub-nociceptive sensation and to examine its pain modulation effects in pain-free subjects and chronic pain patients.;Seventeen patients with chronic low back pain (mean age=41.53 years; pain history years=4.05 years) and eighteen pain-free subjects (mean age=35.78 years). After familiarization training on 5 levels of sub-nociceptive and nociceptive stimuli, the subjects were asked to participate in a perception/imagery experiment with concurrent 128-channel electroencephalogram recording. In perception trials, the participants mentally rehearsed and maintained nociceptive images. In imagery trials, the participants received the nociceptive stimulations, and mentally generated and rehearsed nociceptive images that had previously learnt. They were then to rate the recalled nociceptive images in both types of trials.;T-tests showed significant difference in pain normalized pain rating between two conditions in Level 2 pain in chronic pain group (t(16)=-2.208, p<0.050) and in Levels 1-3 pain (t(17)=-2.630--3.223, p<0.050) in pain-free group. Multivariate repeated measures ANOVA showed more positive amplitudes in P2, P3 and P600 and less negative N400 (p<0.01) in Imagery task among pain-free group. Multivariate repeated measures ANOVA revealed significant between-group differences in P2, P3 and P600. Further analysis revealed that some chronic pain patients (n=6) ("respondents") reported significant pain rating reduction while the rest (n=11) ("non-respondents") did not. ERP analyses showed that the respondent group has significantly larger amplitude of P2 component in the respondents.;Behavioral data suggested that the magnitude of down-modulation was shown to be lessened in chronic pain group, possibly due to pain hypervigilance. It was shown that some chronic pain people were able to modulate pain perception using somatosensory imagery technique. P2 component could be the marker for successful focused attention to nociceptive stimulation for pain attenuation. The sub-nociceptive somatosensory image was generated, as reflected by frontal N400 component. The results suggest the potential therapeutic value of focused attention via imagery for modulating nociceptive perception. |
