Dipolar modelling of the scalp evoked potentials to painful contact heat stimulation of the human skin

Contact heat evoked potentials (CHEPs) were collected in 12 healthy subjects by stimulating the forearm skin with a couple of thermodes at a painful intensity. The stimulated area was 628 mm² and the repetition rate was 0.1 Hz. The electroencephalogram was recorded by 31 electrodes placed on the scalp according to an extended 10-20 System. A dipolar model explaining the scalp CHEP distribution was built by using the brain electrical source analysis. The model includes two dipoles located bilaterally in the perisylvian region, one dipole in the deep midline region and two dipoles located bilaterally in the deep temporal lobe. This dipolar model is very similar to that previously described to explain the topography of evoked potentials to radiant heat stimulation by laser pulses. Since laser stimuli activate the nociceptive fibres, the strong similarity of the cerebral dipoles activated by contact heat stimuli and by laser pulses suggests that only nociceptive inputs are involved in the scalp painful CHEP building. Therefore, CHEP recording can be useful for clinical examination of the nociceptive system.