Effect of Transcranial Magnetic Stimulation to Motor Cortex on Pain Perception and Nociceptive Reflex

Noxious stimulation over the foot can evoke a nociceptive flexor reflex (NR) in the lower limb especially for tibialis anterior muscle (TA). Components of NR include the monosynaptic fast latency NRII, and the polysynaptic slow latency NRIII, supposedly a spinal segmental reflex influenced by the supraspinal control. Pain perception is quantified by visual analogous scale (VAS) and has been reported to be related to NRIII. Previous papers have reported the long lasting effect of transcranial magnetic stimulation (TMS), as well as TMS suppressing pain perception. The purpose of this study was to investigate the immediate and prolonged effect of a single-pulse TMS to suppress NR and pain. NRIII was provoked at right TA by a train of electrical stimulation on the right toe in 10 healthy subjects. TMS was delivered over the vertex area to evoke right anterior tibialis muscle activity. A sham TMS from different directions of the coil was performed on the next day. The NRIII amplitude and VAS were measured. As a result, the amplitude of NRIII was significantly decreased than the control 50 ms pre-stimulation (0.20 +/- 0.13 mA vs. 0.65 +/- 0.42 mV, P = 0.016), 100 ms pre-stimulation (0.10 +/- 0.10 mA vs. 0.65 +/- 0.42 mV, P = 0.001), 15 min post-stimulation (0.12 +/- 0.09 mA vs. 0.65 +/- 0.42 mV, P = 0.004), and 30 min post-stimulation (0.41 +/- 0.21 mA vs. 0.65 +/- 0.42 mV, P = 0.046). VAS was diminished compared with the control 50 ms pre-stimulation (3.3 +/- 0.9 vs. 5.4 +/- 1.3, P = 0.002), 100 ms pre-stimulation (2.6 +/- 0.5 vs. 5.4 +/- 1.3, P < 0.001) and 15 min post-stimulation (3.5 +/- 0.9 vs. 5.4 +/- 1.3, P = 0.046). The NRIII amplitude was well correlated with VAS in reduction during the TMS condition and 15 min after electrical stimulation (P < 0.001). The sham TMS did not suppress NRIII or VAS. In conclusion, our results indicate that NRIII and the nociception can be inhibited by one single pulse TMS and such an effect can last for a period of time.