Pain-related magnetic fields following painful CO2 laser stimulation in man.

The initial somatosensory evoked magnetic fields following painful heat stimulation by CO2 laser beam applied to the upper and lower limb were investigated in normal subjects. The main deflections, 'Pain MA' and 'Pain ML' following the arm and leg stimulation, respectively, were identified in the bilateral second sensory cortices (SII). The onset latencies of Pain MA and Pain ML were approximately 150 and 200 ms, respectively. No consistent equivalent current dipole was found in other areas including the primary sensory cortex in each hemisphere. Therefore, we consider that neurons in the bilateral SII are initially activated following painful heat stimulation.