Applications of Repetitive Transcranial Magnetic Stimulation on Motor Symptoms in Parkinson's Disease

Abstract

various cortical targets, including the primary motor cortex (M1), supplementary motor area (SMA), and left dorsolateral prefrontal cortex (DLPFC), has been reported. After application of high-frequency (HF)rTMS over the M1, most studies have demonstrated that PD patient’s exhibit improved motor function in their hands and gait [10-12]. The HF-rTMS over the M1 suggested being increased motor-related activity in the caudate nucleus. Even so, other studies have reported no beneficial effects of this stimulation [13]. In one study, an rTMS of 5 Hz over the SMA modestly improved motor symptoms in patients with PD [14]. Another study, which aimed to improve disturbance in mood in PD patients by applying rTMS over the DLPFC, demonstrated positive effects on depression level [15]. Moreover, a few other studies have reported positive effects and improvement in motor symptoms in PD patients who received rTMS over the DLPFC [16]. Therefore, optimal parameters for rTMS remain to be established. To address this issue, we sought to identify the best cortical area for HF-rTMS therapy in patients with PD by conducting a double-blind, placebo-controlled, crossover study. After application of HF-rTMS over the M1, SMA, DLPFC and sham, we compared the results to those obtained during sham stimulations [17]. This study reported that the UPDRS-III scores following the application of HF-rTMS over the M1 and SMA was significantly greater than that following sham stimulation. In contrast, changes in UPDRSIII scores following bilateral rTMS over the DLPFC were not different from those after sham stimulation. No significant changes emerged for either the depression or apathy scores following HF-rTMS over any cortical area. Therefore, application of HF-rTMS over the M1 and SMA significantly improved the motor symptoms in patients with PD but did not improve mood disturbances. Many positive studies report improvement of bradykinesia, but diverge in their efficacy to treat other cardinal symptoms of PD. rTMS improved gait in several [18,19], but not all studies [20]. A few studies have reported finding improvement in tremor symptoms in PD patients who received rTMS. At present, the mechanisms of rTMS in relation to disturbances in motor function and mood in PD remain unclear and thus controversial. A hypoactive caudate nucleus may underlie the motor deficits in PD patients by interfering with the normal functioning of the striato-frontal motor loop. Applying HF-rTMS over the M1 may partially compensate for the underactive basal ganglia-thalamocortical outflow to the frontal motor cortical areas