Effects of repetitive transcranial magnetic stimulation on cortical excitability in patients with focal dystonia

1 Hz repetitive transcranial magnetic stimulation (rTMS) at 90% of the active motor threshold over the left lateral premotor region suppress cortical excitability for 15 min or so. This effect is evident after several hundred conditioning stimuli and topographically specific, since stimulation over the motor hand area itself has no significant influence on motor evoked potentials (MEPs). We suggest that measuring the suppression of the MEPs amplitude at the motor "hot spot" after rTMS applied at the left premotor cortex and the left motor hand area provides a model for studying the functional interaction between premotor and motor cortex in healthy subjects and patients with movement disorders such as blepharospasm. Recently, it was demonstrated that 1 Hz rTMS at 90% of the resting motor threshold over the motor hand area improves clinical symtoms in focal dystonia. Yet, it is not clear if the effects of rTMS on cortical excitability were due to a spread of the activity of the stimulating coil, positioned over the motor hand area, to the premotor cortex or due to a direct interaction at the motor hand area. We will test if 1 Hz rTMS at low intensities (90% of the active motor threshold) applied over the premotor cortex has similar or even better effects on clinical symptoms in patients with blepharospasm when compared to rTMS over the motor hand area. Additionally, we will test if 1 Hz rTMS applied over the premotor cortex and the motor hand area produces comparable effects on cortical excitability in patients as in normal subjects.