Repetitive paired-pulse transcranial magnetic stimulation affects corticospinal excitability and finger tapping in Parkinson's disease

To study the effect of long trains of a recently established conditioning-test paired-pulse repetitive transcranial magnetic stimulation (rTMS) paradigm on corticospinal excitability and finger tapping speed.

We applied 900 inhibiting or facilitating paired-pulses or 900 real or sham single stimuli at 1Hz over the motor cortex contralateral to the dominant hand of 9 healthy subjects and contralateral to the more affected hand of 11 patients with Parkinson's disease.

In both groups, motor evoked potentials (MEPs) from suprathreshold pulses were larger after facilitating paired-pulses than after inhibiting paired-pulses. After real single-pulse rTMS and after either type of paired-pulse rTMS patients showed an increase in finger tapping frequency on the stimulated hand. Tapping was unchanged contralaterally, after sham stimuli, and in controls. Tremor and tapping frequencies were not correlated, nor was the change in MEP size correlated to the change in tapping frequency.

Repetitive paired-pulses allow selective induction of corticospinal inhibition or facilitation, but do not enhance the transient improvement of finger motility induced by conventional single-pulse rTMS.