The impact on speech with different deep brain stimulation settings in Parkinson's disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder, characterized by the progressive degeneration of the nigrostriatal dopaminergic pathway which affects movement initiation and maintenance, causing hypokinetic dysarthria in PD. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been widely used to manage rigidity, bradykinesias and drug-induced dyskinesias. While STN DBS successfully manages many symptoms of PD, speech response has been widely reported as “no or negative impact”. The High-Frequency Setting (HFS) is more focused within the STN which is known to control appendicular symptoms. However, the unintentional HFS current spreading to adjacent brain areas, such as the corticospinal and corticobulbar tracts, was thought to contribute to the deterioration of axial symptoms, including speech. The Low-Frequency Setting (LFS) extends more dorsally and ventrally towards surrounding structures, hence does not show the same negative impact and may reduce the negative impact on the axial functions including speech. This double-blind, randomized perception study assesses the impact of two deep brain stimulation (DBS) settings (high-frequency stimulation and interleave-interlink dual-frequency paradigm) on speech produced by 20 patients with PD. The impact of the two testing conditions was different for different Syllable Types with significant negative correlation between the articulatory rate and articulatory accuracy.