Sobell Department of Motor Neuroscience and Movement Disorders, Unit of Functional Neurosurgery, National Hospital of Neurology and Neurosurgery, Queen Square, London, UK
Department of Neurology, University Medical Centre Ljubljana, Slovenia
| [c] Faculty of Medicine, University of Ljubljana, Slovenia
| [d] Faculty of Computer and Information Sciences, University of Ljubljana, Slovenia
Department of Neurology, Innsbruck Medical University, Innsbruck, Austria
Correspondence to: Timothy Grover, Unit of Functional Neurosurgery, UCL Institute of Neurology, National Hospital for Neurology and Neurosurgery, Box 146, Queen Square, London WC1N 3BG, UK. E-mail: firstname.lastname@example.org.
Abstract: Background:Subthalamic deep brain stimulation (STN-DBS) is an established treatment for late stage Parkinson’s disease (PD). Speech intelligibility (SI) and verbal fluency (VF) have been shown to deteriorate following chronic STN-DBS. It has been suggested that speech might respond favourably to low frequency stimulation (LFS). Objective:We examined how SI, perceptual speech characteristics, phonemic and semantic VF and processes underlying it (clustering and switching) respond to LFS of 60 and 80 Hz in comparison to high frequency stimulation (HFS) (110, 130 and 200 Hz). Methods:In this double-blind study, 15 STN-DBS PD patients (mean age 65, SD = 5.8, 14 right handed, three females), were assessed at five stimulation frequencies: 60 Hz, 80 Hz, 110 Hz, 130 Hz and 200 Hz. In addition to the clinical neurological assessment of speech, VF and SI were assessed. Results:SI and in particular articulation, respiration, phonation and prosody improved with LFS (all p < 0.05). Phonemic VF switching improved with LFS (p = 0.005) but this did not translate to an improved phonemic VF score. A trend for improved semantic VF was found. A negative correlation was found between perceptual characteristics of speech and duration of chronic stimulation (all p < 0.05). Conclusions:These findings highlight the need for meticulous programming of frequency to maximise SI in chronic STN-DBS. The findings further implicate stimulation frequency in changes to specific processes underlying VF, namely phonemic switching and demonstrate the potential to address such deficits through advanced adjustment of stimulation parameters.
Keywords: Subthalamic nucleus, deep brain stimulation, Parkinson’s disease, speech intelligibility, verbal fluency, frequency