Abnormal conditioning effect of transcranial magnetic stimulation on soleus H-reflex during voluntary movement in Parkinsonʹs disease

Objectives: The objective of this study is to clarify the participation of cortical motor control abnormality in the motor dysfunction of Parkinsonʹs disease (PD), especially at the onset of movement. Methods: Conditioning effects of transcranial magnetic simulation (TMS) on the soleus (SOL) H-reflex evoked with tibial nerve stimulation were examined in 19 patients with PD and 10 normal volunteers. Experiments were done at rest, during tonic plantarflexion (PF), and at PF onset. Stimulus intensity of TMS was maintained at less than 5% of the motor threshold in each situation. Seven patients underwent pallidotomy and were examined twice, once before and once after the operation. Results: Short latency subthreshold TMS stimulation did not facilitate the SOL H-reflex neither during tonic PF nor at PF onset in the patients with PD, though it was evident in normal subjects. In some patients, paradoxical inhibition appeared at PF onset. The facilitation increase at PF onset, as compared to that at rest, was negatively correlated with the motor part of the unified Parkinsonʹs disease rating scale and with the rigidity grade. Pallidotomy improved both modulation and the clinical scores. Conclusions: Cortical activity for the proper execution of reciprocal control between the agonist and antagonist seems to be disturbed in PD.