2008 年 20 巻 4 号 p. 191-196
[Purpose] It is known that peripheral noxious events provoke sensitization of the peripheral and spinal nervous systems and influence neural transmissions to the brain. In this study, we aimed to examine how brain activation is affected when provoked by electrical stimulation and by prior sensitization with peripheral application of a painful agent (capsaicin). [Subjects] Six normal adult volunteers were enrolled in this study. [Methods] Pain intensity of participants was reported using a visual analogue scale (VAS). Utilizing magnetoencephalography (MEG), changes in the brain's areas and levels of activation were observed by measuring magnetic field alterations. [Results] Locations of equivalent current dipoles (ECDs) changed depending on changes of VAS. The moment (Q) value of the ECDs before the capsaicin cream application was 12.2 ± 6.5 nAm. After applying the capsaicin cream to the left forearm, the Q value increased. The present results suggest that an underlying hyper-responsive condition (neural sensitization) provoked by peripheral capsaicin may cause such changes. Importantly, this study revealed that cortical responses altered in the absence of participant perception of altered pain sensation. [Conclusions] Our findings suggest that alteration of cortical activity may occur when therapeutic electrical stimulations are used after prior pain sensitization.
