Can Decreasing Stimulation Frequency Improve Speech Disorders in Parkinson’s Disease?

Parkinson’s disease (PD) is a chronic and progressive movement disorder affecting millions of people worldwide. Among the myriad symptoms that patients with PD must contend with, dysarthria—a motor speech disorder characterized by slurred or slow speech that can be difficult to understand—is particularly debilitating. One of the treatments that offer significant motor benefits is deep brain stimulation (DBS), especially when targeting the subthalamic nucleus (STN). However, the long-term effects of this intervention on dysarthria have sparked considerable concern.

In a study that has shed new light on the management of speech impairment in PD patients, researchers have uncovered a promising strategy: lowering the frequency of STN-DBS, potentially offering an improved quality of life for those affected by speech difficulties. The findings of this study were published in ‘Parkinsonism & Related Disorders’, with a focus on understanding if low-frequency stimulation (LFS) could sustainably benefit speech intelligibility in PD patients undergoing STN-DBS.

DOI: 10.1016/j.parkreldis.2019.04.018

Parkinson’s disease, characterized by symptoms such as tremors, rigidity, bradykinesia (slowness of movement), and postural instability, can have profound effects on various aspects of daily life, including communication. Dysarthria in PD patients can lead to social withdrawal and negatively impact the overall well-being. Deep brain stimulation of the subthalamic nucleus has been an effective treatment in reducing motor symptoms, but its effect on speech has raised concerns due to reports of worsening dysarthria.

A groundbreaking study, led by Dr. Margherita Fabbri of the Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Portugal (, and her colleagues, evaluated the impact of STN-DBS frequency changes on speech performance in PD patients. This cohort study compared ten PD patients with significant speech impairment with ten patients with milder speech difficulties—all of whom had been treated with STN-DBS.

Patients underwent a series of tests under various conditions: medication off/stimulation off, medication off/stimulation on (at 130 Hz, high-frequency stimulation [HFS]), medication off/stimulation on (at 60 Hz—low-frequency stimulation [LFS]), and medication on with both HFS and LFS. Assessments included measures of voice (such as fundamental frequency and jitter), speech (articulatory diadochokinesis [DDK], pitch variability, rate, and intelligibility), and motor performance (evaluated by the Movement Disorder Society-Unified Parkinson’s Disease Rating Scale [MDS-UPDRS-III]).

The outcomes revealed that for patients who had severe speech impairments, LFS significantly improved DDK and sentence intelligibility compared to no stimulation and HFS in the absence of medication. Interestingly, the benefits of LFS were even more pronounced when patients were on medication, indicating an improvement in speech intelligibility across both patient groups.

As a part of this innovative research, five patients with severe speech impairment chose to continue with LFS. Follow-up assessments conducted after six months showed that the speech benefits were maintained; however, some patients required adjustments to their treatment, highlighting that LFS effects on motor symptoms might not remain constant over time.

This vital research has been underlined by several experts in the field. Dr. Maurizio Zibetti (, from the University of Torino, collaborated on this study, stating that LFS might offer a dual benefit to PD patients, providing both immediate and enduring improvements in speech. However, Zibetti also cautioned that this is not a panacea, as fluctuating effects on motor symptoms can necessitate continuous adjustments to the DBS settings over time.

This study enriches the PD community’s knowledge, as it prompts a re-evaluation of traditional DBS protocols. Dr. Leonardo Lopiano (, from the University of Torino, emphasized the need for personalized DBS approaches that specifically address speech impairments without compromising motor function.

Furthermore, experts like Dr. Joaquim Ferreira ( from the Instituto de Medicina Molecular and Faculdade de Medicina, Universidade de Lisboa, Portugal, underline the importance of a multidisciplinary approach including speech therapy alongside neurostimulation to optimize outcomes for PD patients.

The ramifications of this study hold the potential for a paradigm shift in the treatment of PD-related speech disorders. This new perspective on the balance between motor and non-motor symptom management could lead to enhancements in personalized healthcare for patients with Parkinson’s disease.

As this research progresses, the medical community stands on the brink of a potential revolution in managing dysarthria in PD. With continued investigation, low-frequency deep brain stimulation could become a critical component in the therapeutic arsenal against Parkinson’s disease, providing a voice to those whose speech has been muted by this relentless condition.


1. Fabbri, M. et al. (2019). Is lowering stimulation frequency a feasible option for subthalamic deep brain stimulation in Parkinson’s disease patients with dysarthria? Parkinsonism & Related Disorders, 64, 242–248. DOI: 10.1016/j.parkreldis.2019.04.018
2. Zibetti, M. et al. (2019). University of Torino Profile.
3. Lopiano, L. et al. (2019). University of Torino Profile.
4. Ferreira, J. J. et al. (2019). Instituto de Medicina Molecular and Faculdade de Medicina, Universidade de Lisboa, Portugal Profile.
5. Parkinson’s Disease Foundation. (2021). Retrieved from


1. Parkinson’s Disease and Dysarthria
2. Low-Frequency Stimulation
3. Deep Brain Stimulation Outcomes
4. Speech Impairment in Parkinson’s
5. Subthalamic Nucleus Stimulation