The effect of anodal transcranial direct current stimulation over the primary motor or somatosensory cortices on somatosensory evoked magnetic fields

• We investigated the effect of anodal transcranial direct-current stimulation (tDCS) on somatosensory evoked magnetic fields.
• The source strengths for the P35m and the P60m increased after tDCS was applied over the primary motor cortex (M1) and increased for the P60m after tDCS was applied over the primary somatosensory cortex (S1).
• The mean equivalent current dipole (ECD) location for the P35m was between 10 and 20 min after anodal tDCS was applied over M1 and was located significantly anterior to that of the N20m.

ObjectivesThe purpose of this study was to investigate the effect of anodal transcranial direct-current stimulation (tDCS) applied over the primary motor (M1) or the primary somatosensory (S1) cortices on somatosensory evoked magnetic fields (SEFs) following median nerve stimulation.MethodsAnodal tDCS was applied for 15 min on the left motor or somatosensory cortices at 1 mA. SEFs were recorded following right median nerve stimulation using a magnetoencephalography (MEG) system before and after the application of tDCS. SEFs was measured and compared before and after tDCS was applied over M1 or S1.ResultsThe source strengths for the P35m and P60m increased after tDCS was applied over M1 and that for the P60m increased after tDCS was applied over S1. The mean equivalent current dipole (ECD) location for the P35m was located significantly anterior to that of the N20m, but only during post 1 (10–20 min after tDCS was applied over M1).ConclusionOur results indicated that the anodal tDCS applied over M1 affected the P35m and P60m sources on SEF components, while that applied over S1 influenced the P60m source.SignificanceWe demonstrated anodal tDCS applied over M1 or S1 can modulate somatosensory processing and components of SEFs, confirming the hypothesis for locally distinct generators of the P35m and P60m sources.