Changes of somatosensory function by low frequency transcranial magnetic stimulation over the motor cortex

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Objective : To study changes of current perception threshold (CPT) by repetitive transcranial magnetic stimulation (rTMS) over the motor cortex in humans.Experiment 11. Subjects and Methods : 0.9Hz rTMS over the right motor cortex, sensory cortex and sham stimulation were given to ten healthy subjects (five men and five women ; mean age ± SD, 35.8 ± 5.7). The intensity of rTMS was fixed at 90% of the resting motor threshold at the hand area of motor cortex. 500 stimuli were given in each subject. CPTs (2k, 250, 5 Hz) of the left index finger were determined by using Neurometer^<TM> (Neurotoron, Baltimore, MD), before and after rTMS.2. Results : The CPTs of 2k and 5 Hz were significantly increased after rTMS over the motor cortex, but the changes were within normal limits. Sham stimulation or rTMS over the sensory cortex had no effect on CPTs.Experiment 21. Subjects and Methods : 56-year-old woman with a brain contusion of left fronto- parietal lobe at the age of 51 was the subject. She had right hemiparesis without hypesthesia and hypalgesia. rTMS was given over the left motor cortex in the same condition as the healthy subjects. CPTs (2k and 5 Hz) of the right index finger were determined before and after rTMS.2. Results : CPTs of 2k Hz as well as 5 Hz were decreased.Conclusions2kHz CPT is related to the threshold of Aβ-fiber, and 5Hz CPT is C fiber, and they are involved in tactile sensation and a slow pain respectively. Experiment 1 suggests that rTMS increased the threshold of tactile sensation and a slow pain in a healthy volunteer at the same time. But it remains a within normal limits, and this result suggests to that of the safety of rTMS.At experiment 2, because of limited case, it is unclear whether the result indicates the tendency all patients with brain damage at this moment.