Can we improve speech by subthalamic nucleus Deep Brain Stimulation (STN-DBS) in Parkinson’s disease?
Among the repertoire of motor dysfunctions that charaterize Parkinson's disease (PD), dysarthria denotes a motor speech disorder particularly disabling for individuals with PD. Dysarthria in PD is generally described by a monotony of pitch and loudness, reduced stress, variable rate, imprecise consonants, and a breathy and harsh voice. Its responsiveness to treatments is often mitigated, and thus, the understanding and the management of dysarthria is still challenging for both researchers and clinicians. Notably, subthalamic nucleus deep brain stimulation (STN-DBS) enhances improvement of some motor components of speech production, while intelligibility decreases systematically after surgery. Results available often confirm the lower degree of speech improvement following STN stimulation compared with the global motor state, even demonstrating a potential exacerbation of speech deficits following stimulation. It has been suggested that PD dysarthria is associated with an altered recruitment of the principal brain motor regions (orofacial primary motor cortex, cerebellum) and an increased involvement of premotor and prefrontal cortices (notably the supplementary motor area). This pathological pattern does not parallel the compensatory strategy developed for segmentary motor tasks and may contribute to explain the frequent treatment discrepancies between limb and speech movements. This presentation aims at addressing the pathophysiology of dysarthria in PD, and discussing its characteristics from both neurophysiological and neurolinguistic points of view. Findings and issues related to the effects of STN-DBS on PD speech will also be adressed.