Studies on mechanisms underlying lasting effects of rTMS

点击翻译按钮获取中文摘要

Repetitive transcranial magnetic stimulation (rTMS) has been used for the treatment of several psychiatric and neurological disorders, that suggests that some long term effects should be evoked with this stimulation method. To elucidate mechanisms underlying the long term effects, in the present investigation, our study has focused on the following two points.1. Are distant areas affected with this stimulation?Since nervous systems play their roles through enormous connections within them, effects by rTMS may be produced by activation of distant areas as well as activation of the areas beneath the coil. Modulatory effects on distant areas were studied by combining rTMS over the primary motor cortex with TMS over the contralateral motor cortex, SEP over the ipsilateral sensory cortex, NIRS, SPECT or PET. These results showed that rTMS over the primary motor cortex evoked excitability changes not only in the ipsilateral sensorimotor cortex but also in the contralateral motor cortex, ipsilaeral thalamus and cotralateral cerebellum. Based on these, we conclude that distant areas are also affected by rTMS over a certain area in brain, if they have a tight connection with the directly stimulated area.2. Does rTMS elicit a lasting effect after the stimulation?If rTMS has a beneficial clinical effect, it should have a lasting effect even after the cessation of stimulation. We studied lasting effects on a few areas evoked by rTMS over the primary motor cortex using sensory evoked potential (SEP) or neuroimaging techniques. 1Hz, low intensity, 200 stimuli produced excitability changes lasting at least two hours after the cessation of rTMS From these, we conclude that rTMS can evoke a lasting effect on the central nervous system after rTMS in humans.Based on these findings, one possible explanation for the beneficial effect of rTMS on Parkinson disease is a lasting suppression of the thalamus by rTMS. We may call this as "functional thalamotomy".