After-effect of transcutaneous electrical nerve stimulation (TENS) on pain-related evoked potentials and magnetic fields in normal subjects

Objectives: The after-effect of transcutaneous electrical nerve stimulation (TENS) on pain-related brain responses was investigated using electroencephalography (EEG) and magnetoencephalography (MEG). Methods: We studied 13 healthy volunteers for the main experiment and 7 for the control experiment. The pain-related evoked cerebral potentials (PREP) at Cz and magnetic cortical fields (PRCF) on both hemispheres following painful electrical finger stimulation were simultaneously recorded before and after TENS on the right forearm of the median nerve territory at 50 Hz for 30 min. PREP and PRCF were similarly recorded without TENS in the control experiment. Results: The PREP components, N150 and P220, were significantly attenuated after TENS, compared to those before TENS (P<0.01, two-way repeated ANOVA). However, there was no consistent change of the PRCF components. Eleven of 13 subjects reported no change of pain sensation after TENS. There was no change of PREP in control experiment without TENS. Conclusions: The results indicated that TENS reduced PREP following painful electrical stimulation, and that the origin of PREP was, at least partially, different from that of PRCF which was not changed after TENS. An after-effect of TENS significantly affected the generation process of PREP, but it was not enough to relieve the subjective painful feeling.