Parkinson’s disease (PD) is one of the most common degenerative diseases of the nervous system in the middle-aged and elderly. Clinically, it is characterized by delayed movement, static tremor, muscle rigidity, and postural gait disorders (Postuma et al., 2015; Erro and Stamelou, 2017; Jankovic and Tan, 2020). Freezing of Gait (FOG) is a prevalent and severely debilitating gait disorder observed in the middle and advanced stages of PD patients. It mainly presents with hesitation to start walking, and patients often experience a sensation of their feet being firmly rooted to the ground, typically lasting for several seconds. In severe instances, walking inability may occur (Gao et al., 2020). The occurrence of FOG is typically observed during initiation, turning, navigating narrow spaces, and approaching a target. Environmental factors, emotional cognition, and other variables exert significant influence on FOG (Spildooren et al., 2019; Ehgoetz Martens et al., 2020; Weiss et al., 2020). The prevalence of FOG increases with disease progression, as evidenced by a 12-year longitudinal study reporting a substantial incidence rate of 63% in PD patients with an illness duration exceeding 10 years (Forsaa et al., 2015). Furthermore, FOG poses elevated risks for falls and fractures while also giving rise to adverse psychological issues such as anxiety and depression, thereby severely impacting the patient’s quality of life (Bekkers et al., 2017; Okuma et al., 2018; Witt et al., 2019).

Due to the heterogeneous clinical manifestations and underlying pathophysiological mechanisms associated with FOG, pharmacological interventions and deep brain stimulation (DBS) are not considered optimal for its amelioration. In recent years, increasing attention has been directed toward the unique efficacy of physical therapy in addressing FOG (Dagan et al., 2018; Gilat et al., 2018; Cosentino et al., 2020; Delgado-Alvarado et al., 2020). Repetitive transcranial magnetic stimulation (rTMS), a non-invasive neuroregulation technique based on the principle of magnetic induction, induces current flow and action potentials within the cerebral cortex through pulsed magnetic fields. This can modulate brain metabolism and related electrophysiological activities (Burke et al., 2019; Lefaucheur, 2019).

In 2020, the latest European clinical guidelines recommended rTMS over the bilateral primary motor cortex (M1) as a Grade-B recommendation for improving motor function in PD (Burke et al., 2019; Lefaucheur et al., 2020). The efficiency of this approach has been confirmed by multi-center clinical trials and meta-analyses (Burke et al., 2019; Lefaucheur et al., 2020). Li et al.’s study (Li et al., 2018), based on resting-state functional magnetic resonance imaging (fMRI), found synchronous decreases in spontaneous neural activity within the bilateral M1 region and subparietal lobule of the brain in patients with PD-related FOG (PD-FOG). Furthermore, according to the “decoupling model” (Plotnik et al., 2012), it is suggested that patients with FOG have difficulty initiating or experiencing freezing due to impaired integration between M1-mediated walking initiation and postural adjustment mediated by the supplementary motor area (SMA) (Nomura and Kirimoto, 2018; de Lima-Pardini et al., 2020; Tsuru et al., 2020). Previous studies have reported that high-frequency rTMS applied to M1 can enhance the local excitability of the primary motor cortex and indirectly activate SMA neural activity (Bestmann et al., 2003). As suggested previously (Kim et al., 2015), high frequency rTMS over the lower leg primary motor cortex of the dominant hemisphere may be an effective treatment for alleviating FOG in PD. Furthermore, FOG usually manifests as problems with bilateral coordination between the legs. Therefore, we hypothesize that targeting the bilateral M1 region with rTMS will get a better therapy response for improving FOG in PD.

Additionally, anxiety and depression have been associated with FOG and the M1, premotor cortex, and prefrontal regions are interconnected through the frontal longitudinal system (FLS) (Komaitis et al., 2019). While some clinical studies have reported the effects of motor cortex rTMS on motor symptoms in PD, limited research exists exploring its effects on non-motor symptoms, such as anxiety, depression, and cognition function. Thus, our main objective was to investigate the clinical efficiency of high-frequency rTMS targeting the bilateral M1 for treating FOG in PD while also observing its effects on walking ability, overall motor function, anxiety, depression, and cognition among these patients. In addition, previous studies have limitations of small sample sizes. The present study recruited more subjects in the rTMS group than other research. This study will provide new evidence of high-frequency rTMS over the bilateral M1 serving as an therapy for alleviating FOG in PD patients.

This randomized, double-blind, and sham-controlled study demonstrated that high-frequency rTMS stimulation over the bilateral M1 can lead to a short-lasting improvement in FOG in patients with PD. Additionally, there was some relief observed in the patients’ motor symptoms as well as anxiety and depression symptoms. Notably, the FOG improvement was found to be associated with a reduction in anxiety and depression and the effects of high-frequency rTMS on FOG were cumulative and continued for at least 30 days after treatment. Our findings suggest that high-frequency rTMS over the bilateral M1 may be considered a feasible treatment option for FOG in PD.

In recent years, rTMS has had widespread usage as a non-invasive neuromodulation technique for treating various conditions, including PD, stroke, depression, and other neuropsychiatric disorders (Guo et al., 2017; Dionísio et al., 2018; Latorre et al., 2019; Leung et al., 2020). While several studies both domestically and internationally, have reported the effects of motor cortex rTMS on motor symptoms of PD (Chou et al., 2015; Yang et al., 2018; Latorre et al., 2019), only two clinical reports exist regarding the use of FOGQ as an observation index for assessing the impact of M1 rTMS on FOG in PD (Rektorova et al., 2007; Kim et al., 2015).

Rektorova et al. (2007) were among the first to report on the efficacy of rTMS for alleviating FOG symptoms in PD patients using a cross-over experimental design. However their findings indicated that stimulating the left M1 area or left DLPFC did not improve FOGQ scores, which contradicts our positive results. According to previous studies based on the “threshold model” theory (Plotnik et al., 2012) along with numerous others (Kleiner et al., 2018; Son et al., 2018; Spildooren et al., 2019), it is understood that FOG is linked to asymmetry and coordination issues within gait patterns involving both lower limbs; clinically it often presents itself through more severe unilateral symptoms. In Rektorova et al.’s study, only the left motor cortex was stimulated, and the researchers did not report the side with more severe lower limb motor symptoms in 4 subjects.

The study by Rektorova et al. included only four subjects, which may have introduced bias into the results. Furthermore, Kim et al. (2015) suggested that rTMS treatment can enhance cortical excitability in PD-FOG and this effect can last for 1 week after treatment, indicating that rTMS may lead to long-term improvement of FOG through cumulative increase in synaptic efficacy. These findings are consistent with our study, demonstrating that high-frequency rTMS in the M1 region can improve FOG symptoms in PD patients.

Importantly, our research results showed a significant decrease in the FOGQ score at T2 compared to T1, suggesting there can be a long-term positive effect (at least 30 days) of high-frequency rTMS on FOG (Latorre et al., 2019). Meta-analysis has shown that the effectiveness and duration of rTMS depend on factors such as total number of pulses, number of stimuli, and interval (Chou et al., 2015), with Bäumer et al. (2003) having demonstrated cumulative changes in cortical excitability with multiple consecutive sessions of rTMS. Therefore, multi-temporal high-frequency rTMS could achieve sustained effects by repeatedly inducing synaptic plasticity and promoting synaptic long-term potentiation from transient to more lasting states.

The mechanism underlying rTMS treatment for FOG in PD remains unclear, but it may be associated with alterations in related neural pathways and neurotransmitters. High-frequency rTMS applied to the M1 region might directly influence striatal activity by activating the motor cortex-thalamus-basal ganglia pathway and subsequently modulating inhibitory impulses within the medial globus pallidus to improve FOG (Kim et al., 2015). Similarly, positron emission computed tomography (PET) studies have indicated (Strafella et al., 2005) that high frequency (10 Hz) rTMS applied to M1 could induce local release of endogenous dopamine within the ipsilateral putamen via cortico-basal ganglia circuits, this is consistent with anatomical projections observed previously. Khedr et al. (2007) treated 20 patients with moderate to severe PD with high frequency (25 Hz) rTMS in the M1 region once a day for 6 consecutive days, with 3,000 pulses per time. Their study found that the serum dopamine level of PD patients was significantly higher than the baseline after all treatments, which was related to the improvement of clinical motor symptoms.

Mi et al. (2020) found that high-frequency rTMS over the bilateral SMA could effectively improve gait disorders by improving the abnormal brain network connectivity pattern related to FOG symptoms in PD patients and making them more similar to people without PD. It has been reported that high-frequency rTMS in the M1 region can increase the blood oxygen level-dependent signal of SMA, that is, indirectly activate the neural activity of SMA (Bestmann et al., 2003). Therefore, we hypothesize that high frequency rTMS in the M1 region in this study may have promoted synaptic activation of SMA by enhancing the interaction between functionally connected SMA-M1, and then improving the freezing gait by normalizing the brain functional connectivity pattern.

In our research, significant reduction of the UPDRS III score was observed following high-frequency rTMS stimulation over the bilateral M1, indicating that this method may ameliorate patients’ motor symptoms. A meta-analysis conducted by Zanjani et al. (2015) evaluated the efficacy of M1 rTMS on motor symptoms in PD patients and revealed that short-term M1 rTMS treatment significantly diminished UPDRS III scores compared to sham stimulation, which is in line with our findings. Both high-frequency and low-frequency rTMS applied to the M1 region potentially induce transient release of endogenous dopamine in the striatum, thereby exerting an immediate impact on PD motor symptoms (Latorre et al., 2019). Subsequently, Kim et al. (2018) investigated the efficacy of various rTMS frequencies on motor function in PD and observed significant UPDRS III score reduction following both high-frequency and low-frequency stimulation treatments. However, the improvement was more pronounced in the high-frequency treatment group, and the effect was maintained for only 1-month post-rTMS in this group. Both high and low frequency rTMS on M1 have the potential to enhance PD patients’ motor function, albeit with high frequency rTMS being more efficacious in mitigating motor symptoms and demonstrating a longer-term positive impact.

In the present study, no statistically significant changes were observed in MMSE and MoCA scores across different time points in either the treatment or control group, suggesting that high-frequency rTMS over the bilateral M1 fails to enhance cognitive function in PD-FOG. Interestingly, the scores of HAMD-24 and HAMA-14 were significantly improved at both T1 and T2 time points in the rTMS group compared to T0 time points. To date, no reports have been published on the efficacy of M1 rTMS in relation to PD-FOG mood disorders.

Anxiety independently contributes to severity of FOG in people with PD (Pimenta et al., 2019) and depressive symptoms may increase the risk of future development of FOG (Herman et al., 2019). In this study, high-frequency stimulation of the M1 region led to an improvement in depression and anxiety symptoms, and the reduction of depression and anxiety scores was significantly correlated with the improvement of the FOGQ. We postulate that the alleviation of depression and anxiety may contribute to the improvement of PD-FOG symptoms, which is consistent with previous research (Cui and Lewis, 2021). Mood disorders are primarily associated with the function of the prefrontal cortex (Samara et al., 2018; Xu et al., 2019), and the M1, premotor cortex, and prefrontal regions are interconnected through the FLS (Komaitis et al., 2019), which might play a role in integrating the activity of local networks within different frontal lobes. The total sessions of rTMS in this study were 10. It is uncertain whether more sessions will result in better treatment effects since few existing study designs have more than 10 sessions (Deng et al., 2022). Further research is required to establish optimal study design that may induce potentially more beneficial outcomes and this may require trying different combinations of stimulation targets.

This study corroborated the significant amelioration of gait freezing, walking ability, global motor function, and depression and anxiety symptoms in PD patients by administering high-frequency rTMS over the bilateral M1. Our results provide powerful evidence of high-frequency rTMS serving as a safe and effective add-on therapy for improving FOG and reducing anxiety and depression symptoms, and also enrich the therapeutic mechanism from a new perspective. However, several limitations should be considered. Firstly, symptom assessment and rTMS treatment were conducted during the “on” phase of the study, due to the inconvenience of outpatients attending the hospital during a fixed “off” phase daily. Consequently, this study’s findings convey the adjunctive efficacy of rTMS in addition to conventional drug therapy. Secondly, the integration of a neuronavigation positioning system, if feasible, could enhance the accuracy of target stimulation and site adjustments in the current rTMS target localization. Thirdly, the sample size of this study was modest and only monitored the subjects for 30 days post-treatment. Nonetheless, the efficacy of rTMS might persist for up to 3 months or even longer. Future research should incrementally enlarge the sample size and explore the long-term implications of rTMS on FOG.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by the Affiliated Hospital of Xuzhou Medical University Ethics Committee. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

WS: Conceptualization, Writing – original draft. ZZ: Data curation, Methodology, Writing – original draft. BL: Methodology, Writing – original draft. JL: Methodology, Writing – original draft. HC: Supervision, Writing – original draft. ShZ: Supervision, Writing – original draft. JZu: Supervision, Writing – original draft. LD: Supervision, Writing – original draft. CX: Supervision, Writing – original draft. MZ: Methodology, Writing – original draft. TZ: Methodology, Writing – original draft. RX: Methodology, Writing – original draft. JZh: Methodology, Writing – original draft. TS: Methodology, Writing – original draft. SuZ: Methodology, Writing – original draft. CC: Methodology, Writing – original draft. SH: Methodology, Writing – original draft. XW: Methodology, Writing – original draft. YN: Methodology, Writing – original draft. KA: Data curation, Writing – original draft. QX: Supervision, Writing – review & editing. XZ: Funding acquisition, Writing – review & editing. GC: Conceptualization, Supervision, Writing – review & editing. WZ: Conceptualization, Writing – review & editing.