Effect of stimulation frequency on quality of speech in individuals with Parkinson’s disease who have undergone sub thalamic nucleus Deep Brain Stimulation surgery

Deep Brain Stimulation (DBS) targeting the subthalamic nucleus (STN) has been successful in improving the core motor symptoms, including motor fluctuations and speech systems, even in advanced stages of Parkinson’s Disease (PD). Given that the DBS frequency setting influences speech intelligibility, it is important to determine the ideal frequency setting while programming DBS to minimize reduction in speech quality postoperatively in individuals with PD. To compare and contrast the effects of stimulation frequency (High, Low, DBS off state) in subthalamic nucleus Deep Brain Stimulation (STN-DBS) on the quality of speech in individuals with PD. Subjective and objective measures of articulation and voice parameters were estimated in low as well as high stimulation frequencies and the DBS-off state for six individuals with PD treated with STN-DBS. Friedman’s Two-way ANOVA yielded significant differences in objective measures of voice ( p < 0.05) only, however there was no statistically significant difference between the low, high stimulation frequency and DBS off state on the articulatory and subjective voice parameters. The site of DBS insertion in the STN, the spread of current to adjacent pathways during high-frequency stimulation, the duration of disease, and the dosage of medication post-DBS surgery can cause detrimental effects on the quality of speech compared to motor movements. Low-frequency stimulation can improve speech scores, but it may also lead to a decline in motor function. On the contrary, a high stimulation frequency is effective in controlling tremors and body movements but may result in a decrease in speech scores. The extent of speech deterioration caused by a high stimulation frequency varies among patients, emphasizing the need for individualized programming of deep brain stimulation (DBS) parameters along with holistic rehabilitation for speech to balance motor and speech outcomes. Changes in the DBS stimulation frequency can alter speech and motor characteristics in individuals with Parkinson’s disease. Hence, while programming DBS stimulation parameters, it needs to be tailored to the individual patient’s needs, balancing the motor function with speech outcomes.