Pain-related somatosensory evoked magnetic fields following lower limb stimulation

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Abstract

Somatosensory evoked magnetic fields (SEFs) following painful electrical stimulation of the sural nerve were examined in 6 normal subjects. Equivalent current dipoles (ECDs) of the deflections shorter than 100 ms in latency were located in the foot area of the primary sensory cortex (SI) in the contralateral hemisphere following both weak and painful stimulations. Two main deflections, N150m-P150m and N250m-P250m, were independently identified only following painful stimulation. ECDs of the N150m-P150m were considered to be located in bilateral second sensory cortices (SII). ECDs of the N250m-P250m were identified in multiple areas including bilateral cingulate cortices and SII. These findings were consistent with the pain-related SEFs following upper limb stimulation. Therefore, we considered that bilateral SII and the cingulate cortices were activated by the painful stimulation and that pain-specific brain activities in those areas did not depend on the stimulation site. © 1997 Elsevier Science B.V. All rights reserved.

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Subjects and methods

Six normal volunteers (2 females and 4 males; mean age 32 years, range 29 to 41 years; mean height 167 cm, range 151 to 175 cm) were studied. Five of the 6 subjects had been also examined in our previous study (Kitamura et al., 1995) on pain-related SEFs following finger stimulation. Informed consent was obtained from all participants prior to the study.

The electric stimulus was a constant voltage square-wave 5-pulse train (0.2 ms pulse duration, 100 Hz pulse frequency) delivered

Short-latency components with latency shorter than 100 ms

When the probe was centered around the Cz, four main deflections, P37m-N45m-P60m-N75m and their counterparts N37m-P45m-N60m-P75m were identified (Fig. 1) in both ‘painful’ and ‘weak’ sessions in all subjects, but their amplitudes were small and their latencies were prolonged in the ‘weak’ session. Their ECDs were located in the foot area of SI in the right hemisphere (Fig. 2). These findings were compatible with our previous report, in which short-latency SEFs following stimulation of the

Discussion

There have been many reports concerning pain-related SEPs following electrical stimulation of the upper limb (Chen et al., 1980; Bromm and Scharein, 1982; Stowell, 1984; Boulu et al., 1985; Willer et al., 1985; Katayama et al., 1985; Miltner et al., 1989; Ohara, 1989; Ohara, 1990; Dowman and Goshko, 1992; Dowman and Darcey, 1994; Dowman, 1994a; Dowman, 1994b), but only few papers (Boulu et al., 1985; Willer et al., 1985; Dowman and Goshko, 1992; Dowman and Darcey, 1994) reported pain-related

Acknowledgements

The authors are very grateful for the technical help of Mr. Y. Takeshima and Mr. O. Nagata. This study was supported by the Uehara Memorial Foundation and the Naito Foundation in Japan, The Integrative Studies on Physiological Functions (06NP0101) from The Ministry of Education, Science and Culture of Japan.

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