ETD

• Parkinson’s disease; speech; STN-DBS

Speech impairment is a common and progressive manifestation of Parkinson’s disease
(PD), affecting up to 89% of patients during the disease course and often becoming
particularly disabling in later stages, when it may respond poorly to conventional
treatment. This thesis investigates subthalamic nucleus (STN) local field potentials
(LFPs) in PD patients treated with chronic conventional deep brain stimulation
(cDBS), with the aim of identifying neural markers associated with speech production
and speech impairment under ecologically relevant conditions. STN activity was
analysed during rest and during two naturalistic speech modalities, reading and
monologue, using spectral, burst-related, and interhemispheric connectivity measures.
Speech production was associated with a reduction in alpha and high-beta power, an
increase in gamma power, and enhanced gamma-band interhemispheric coherence.
As far it concerns markers of speech impairment, considered here mainly in terms of
articulatory precision and intelligibility, worse speech performance was associated
with several resting-state STN features, including higher alpha power, lower beta
peak central frequency, shorted, less frequent and weaker bursts, as well as a reduced
interhemispheric low-beta coherence during task. Overall, these findings provide an
extensive characterization of STN activity in relation to speech dysfunction in PD
and support the relevance of subthalamic markers for more speech-sensitive DBS
assessment and optimization.