Characterization of cortical source generators based on electroencephalography during tonic pain.

Objective: The aim of the present study was to characterize the cortical source generators evoked by experimental tonic pain.

Methods: Electroencephalography (EEG) was recorded on two separate days during rest and with immersion of the hand in ice water for 2 minutes (cold pressor test). Exact low-resolution brain electromagnetic tomography source localization was performed in 31 healthy volunteers to characterize the cortical source generators.

Results: Reliability was high in all eight frequency bands during rest and cold pressor conditions (intraclass coefficients =0.47-0.83 in the cingulate and insula). Tonic pain increased cortical activities in the delta (1-4 Hz), theta (4-8 Hz), beta1 (12-18 Hz), beta2 (18-24 Hz), beta3 (24-32 Hz), and gamma (32-60 Hz) bands (all <0.011) in widespread areas mainly in the limbic system, whereas decreased cortical activities were found in cingulate and pre- and postcentral gyri in the alpha2 (10-12 Hz) band (=0.007). The pain intensity was correlated with cingulate activity in the beta2, beta3, and gamma bands (all <0.04).

Conclusion: Source localization of EEG is a reliable method to estimate cortical source generators. Activities in different brain regions, mainly in the limbic system, showed fluctuations in various frequency bands. Cingulate changes were correlated with pain intensity.

Significance: This method might add information to the objective assessment of the cortical pain response in future experimental pain studies.