Ž . Brain Research 853 2000 282–289 www.elsevier.comrlocaterbres Research report Primary somatosensory cortex is actively involved in pain processing in human Masutaro Kanda a,b , Takashi Nagamine a , Akio Ikeda a , Shinji Ohara a , Takeharu Kunieda a,c , Naohito Fujiwara a , Shogo Yazawa a , Nobukatsu Sawamoto a , Riki Matsumoto a , Waro Taki d , Hiroshi Shibasaki a,e, ) a Department of Brain Pathophysiology, Kyoto UniÕersity Graduate School of Medicine, Kyoto 606-8507, Japan b Department of Neurology, Takeda General Hospital, Kyoto 601-1495, Japan c Department of Neurosurgery, Kyoto UniÕersity Graduate School of Medicine, Kyoto 606-8507, Japan d Department of Neurosurgery, Mie UniÕersity School of Medicine, Tsu 514-8507, Japan e Department of Neurology, Kyoto UniÕersity Graduate School of Medicine, Kyoto 606-8507, Japan Accepted 26 October 1999 Abstract Ž . We recorded somatosensory evoked magnetic fields SEFs by a whole head magnetometer to elucidate cortical receptive areas Ž . involved in pain processing, focusing on the primary somatosensory cortex SI , following painful CO laser stimulation of the dorsum of 2 Ž the left hand in 12 healthy human subjects. In seven subjects, three spatially segregated cortical areas contralateral SI and bilateral Ž . . second SII somatosensory cortices were simultaneously activated at around 210 ms after the stimulus, suggesting parallel processing of Ž . pain information in SI and SII. Equivalent current dipole ECD in SI pointed anteriorly in three subjects whereas posteriorly in the remaining four. We also recorded SEFs following electric stimulation of the left median nerve at wrist in three subjects. ECD of CO 2 laser stimulation was located medial–superior to that of electric stimulation in all three subjects. In addition, by direct recording of Ž . somatosensory evoked potentials SEPs from peri-Rolandic cortex by subdural electrodes in an epilepsy patient, we identified a response to the laser stimulation over the contralateral SI with the peak latency of 220 ms. Its distribution was similar to, but slightly wider than, that of P25 of electric SEPs. Taken together, it is postulated that the pain impulse is received in the crown of the postcentral gyrus in human. q 2000 Elsevier Science B.V. All rights reserved. Ž . Keywords: Pain perception; Magnetoencephalogram; Primary somatosensory cortex SI ; Subdural recording; Parallel processing; Human 1. Introduction Ž . Role of primary somatosensory cortex SI in pain processing in human has been controversial. By using Ž . positron emission tomography PET , some authors re- w ported that the SI was activated by pain stimulus 5,11, x 13,40 , while others did not find significant activation in SI w x 9,22,37,44,47 . It should be kept in mind, however, that PET demonstrates an image constructed by the summated activities of regional cortical areas throughout the measur- ) Corresponding author. Department of Brain Pathophysiology, Kyoto University Graduate School of Medicine, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan. Fax: q81-75-751-3202; e-mail: shib@kuhp.kyoto-u.ac.jp ing period, and thus it does not necessarily reveal transient activities of neurons. Studies using functional magnetic Ž . resonance image fMRI , which is superior to PET in terms of time resolution, did not reveal activation in SI by w x pain stimulation 12,15 . By using CO laser stimulation of the skin which 2 w x selectively activates A d and C nociceptors 7,42 , so- Ž . matosensory evoked potentials SEPs recorded from the human scalp showed cortical activities related to pain w x 8,24,25,33,41,48 . However, the precise location of the generators for these potentials is uncertain because the potentials recorded over the head are distorted by the structures surrounding the brain; cerebrospinal fluid, dura, w x bone and scalp 38 . Compared with PET or fMRI, magnetoencephalogram Ž . MEG has advantages both in temporal and spatial resolu- w x tion for the detection of cortical activities 19 . By using Ž . MEG, both SI and the second somatosensory cortices SII 0006-8993r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0006-8993 99 02274-X