Cortical Neurophysiological Modification after Peripheral Neuronal Sensitization

Abstract

Abstract. [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.

Comparison of the effective intensity of transcutaneous electrical nerve stimulation contralateral to a pain site for analgesia

“…However, previous studies 22 , 23 , 24 ) have shown the same tendency. The reasons may include analgesia to central sensitization 26 , 27 , 28 ) , the descending pain modulatory system 24 , 34 , 35 ) , DNIC 25 ) , and release of endogenous opioid peptides 35 , 36 ) .…”

“…TENS has been used as an analgesic treatment for central sensitization induced by pain stimulus, and the effects have been reported 26 , 27 , 28 ) . The analgesic effects of the treatment to central sensitization is based on TENS to the site of pain.…”

“…However, previous studies [22][23][24] have shown the same tendency. The reasons may include analgesia to central sensitization [26][27][28] , the descending pain modulatory system 24,34,35) , DNIC 25) , and release of endogenous opioid peptides 35,36) . The duration of the stimulus in this study was 60 seconds, which was shorter than the 30 minutes in the previous study, and it is possible that the analgesic tolerance was not adequately considered.…”

“…There have been reports of the use of various stimulus intensities for TENS, including comfortable stimulus intensities based on gate control theory 21 ) and strongest possible intensities 22 , 23 , 24 ) that induce diffuse noxious inhibitory controls (DNIC) 25 ) . Furthermore, TENS has the potential to exert analgesic effects on central sensitization, expanding the therapeutic area 26 , 27 , 28 ) . On the contrary, there are only scattered reports comparing the analgesic effects of contralateral intensity of the stimulus and focusing on changes in sympathetic and parasympathetic nerves in the autonomic nervous system 29 , 30 , 31 ) .…”

Comparison of the pain-relieving effects of transcutaneous electrical nerve stimulation applied at the same dermatome levels as the site of pain in the wrist joint

“…There are no published reports that discuss the effects of TENS applied simultaneously to the site contralateral to the site of pain and to the neck at the same dermatome level as the site of pain. Moreover, almost no current reports discuss the relationship between changes in pain and brain activity after TENS 6 ) .…”