Effects of repetitive transcranial magnetic stimulation on somatosensory evoked potentials and high frequency oscillations in migraine

Background: In previous studies we found that high-frequency somatosensory oscillations (HFOs) reflecting thalamo-cortical activation were decreased in migraineurs between attacks and that high-frequency repetitive transcranial magnetic stimulation (rTMS) was able to normalize the habituation deficit of visual evoked potentials (VEPs). Here we study the effects of activating (10 Hz) or inhibiting (1 Hz) rTMS on conventional low-frequency (LF) and high-frequency somatosensory evoked potentials (SSEPs). Subjects and methods: rTMS was applied on the motor cortex of 13 healthy volunteers (HVs) and 13 migraine without aura (MO) patients. We measured N20-P25 LF-SSEP amplitude and habituation, and maximal peak-to-peak amplitude of early and late HFOs before and after rTMS. Results: In HVs, 1Hz rTMS significantly reduced the amplitude of the first LF-SSEP block and its habituation. In MO patients, 10 Hz rTMS increased the amplitude of the first block and induced habituation. Ten Hz rTMS produced an increase of late HFO in both groups, but more interestingly, in MO patients also significantly increased the early HFOs, which are reduced at baseline compared to those of HVs. Conclusions: These data confirm for SSEP that excitatory rTMS can normalize habituation in migraine patients and show that this is accompanied by early an HFO increase, which is thought to reflect thalamo-cortical activity. Taken together with similar effects we observed for VEPs, this finding supports the hypothesis that dysfunctioning thalamo-cortical loops may be responsible for the interictal habituation deficit in migraine.