Attentional modulation of human pain processing in the secondary somatosensory cortex: a magnetoencephalographic study.

The influence of attention on the processing of pain in the secondary somatosensory cortex (SII) was analyzed using magnetoencephalography in response to painful infra-red heat stimuli applied to the left hand in six male healthy subjects, aged 22-28 years. Three experimental paradigms were chosen to deliver attention dependent results under comparable levels of vigilance. Single moving dipole sources for the pain-evoked responses were calculated in the individual cortex anatomy determined by magnetic resonance imaging. Though pain stimuli followed the same intensity pattern in all paradigms, evoked SII activity increased markedly from the low attention task to the mid-level attention task (P < 0.001). In contrast, further increase of attention from mid-level to high was not accompanied by an additional enhancement of SII activity. It therefore is concluded that activation patterns of SII follow a saturation function which cannot be enlarged by maximizing the relevance of the painful stimuli.