Decreased sensory cortical excitability after 1 Hz rTMS over the ipsilateral primary motor cortex

Objectives: To study changes in the excitability of the sensory cortex by r epetitive transcranial magnetic stimulation (rTMS) in humans. Methods: Somatosensory evoked potentials (SEPs) and antidromic sensory nerv e action potentials (SNAPs) were elicited by right median nerve stimulation at the wrist before and after low frequency (I Hz) rTMS over the left moto r cortex, lateral premotor cortex, sensory cortex, and also after sham stim ulation. The intensity of rTMS was fixed at 1.1 times the active motor thre shold at the hand area of motor cortex. Results: N20 peak (N20p)-P25 and P25-N33 amplitudes were suppressed after r TMS over the motor cortex, whereas the N20 onset (N20o)-N20p and SNAP ampli tudes were not affected. They recovered to the baseline about 100 min after the rTMS. rTMS over the premotor cortex or sensory cortex or sham stimulat ion had no suppressive effect on SEPs. Conclusions: The reduction of N20p-P25 and P25-N33 components without any c hanges of N20o-N20p amplitude suggests that the suppression occurs in the s ensory cortex. rTMS (I Hz) of the motor cortex induces a long-lasting suppr ession of the ipsilateral sensory cortex even at an intensity as low as 1.1 times the active motor threshold. probably via cortico-cortical pathways b etween motor and sensory cortex. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.