Laser-evoked potentials in human pain - II. Cerebral generators

In Part II, the dynamic topography of laser-evoked brain potentials (LEPs) in human pain is reviewed. The cerebral generators of LEPs, SI, SII, and midline deep generators, are then systematically examined, and the results of LEPs and positron-emission tomography (PET)/functional magnetic resonance imaging (fMRI) in pain studies are compared. The theoretical ground of functional segregation and integration of pain processing in the brain can be delineated. Four contending issues are raised: (1) which to use: electroencephalography or magnetoencephalography?, (2) what are the reliability and validity of source localization in LEPs?, (3) can neural generators of LEPs contribute to PET/fMRI of human pain?, and (4) is there a "holy grail" of pain in the brain? Future directions needed for developing comprehensive neurophysiology of pain mechanisms using dynamic topography/source modeling of LEPs with PET/fMRI neuroimaging are discussed. It is concluded that full understanding of the cerebral genesis of LEPs requires empirical identification of their cortical/subcortical substrates, as well as theoretical modeling of their modular function during sequential and parallel stages of human pain processing in the brain.