Triple transcranial static magnetic field stimulation system can suppress the neural activity in the lumbar spinal cord

Transcranial static magnetic field stimulation (tSMS) utilizing a small and strong neodymium (NdFeB) magnet is a non-invasive brain stimulation method with advantages of the safety, simplicity, and inexpensiveness. While tSMS has demonstrated the ability to suppress brain functions below the magnet, the neuromodulatory effects on the spinal cord remain unclear. This study aimed to investigate the neuromodulatory effects of tSMS on the lumbar spinal cord. We applied tSMS over the lumbar spinal cord for 20 min in 15 healthy subjects. The H reflex, served as an index of excitability in the lumbar spinal cord, was recorded from the right soleus muscle following stimulation of the right tibial nerve before (pre), immediately after (post0), and 15 min after (post15) the tSMS. This study was conducted using a crossover design with real and sham tSMS. Triple tSMS system ("SHIN jiba") was used for real stimulation, while a non-magnetic device identical in size and appearance to SHIN jiba was used for sham stimulation. We found that the H-reflex was significantly suppressed in post0 compared to pre in the real condition and that there was no significant difference among pre, post0, and post15 in the sham condition. This study showed that tSMS over the lumbar spinal cord suppressed the neural activity below the magnets immediately after stimulation. tSMS over the lumbar spinal cord has the potential to be a promising non-invasive stimulation technique for suppressing spinal cord excitability.