Parallel activation of primary and secondary somatosensory cortices in human pain processing

Cerebral processing of pain has been shown to involve primary (SI) and seco ndary (SII) somatosensory cortices. However, the temporal activation patter n of these cortices in nociceptive processing has not been demonstrated so far. We therefore used whole-head magnetoencephalography to record cortical responses to cutaneous laser stimuli in six healthy human subjects. By usi ng selective nociceptive stimuli our results confirm involvement of contral ateral ST and bilateral SII in human pain processing. Beyond they show for the first time simultaneous activation onset of contralateral SI and SII af ter similar to 130 ms, indicating parallel thalamocortical distribution of nociceptive information. This contrasts to the serial cortical organization of tactile processing in higher primates and instead corresponds to the pa rallel cortical organization in lower primates and nonprimates. Thus our fi nding suggests preservation of the basic mammalian parallel organizational scheme in human pain processing, whereas in the tactile modality parallel o rganization appears to be abandoned in favor of a serial processing scheme. Functionally, preservation of direct access to SII underscores the relevan ce of this area in human pain processing, probably reflecting an important role of SII in nociceptive learning and memory.