Corticobulbar Activity in Healthy Humans and Parkinson's Disease: A Novel Biomarker for Motivational Arousal?

Background: The corticobulbar (CB) tract, which connects the motor cortex to oral and facial muscles, plays a critical role in reward processing and motivational arousal. Its function is closely associated with dopaminergic pathways, which are disrupted in Parkinson's Disease (PD). This study aims to explore CB excitability as a potential biomarker for motivational arousal in both healthy individuals and PD patients.In Study 1, surface electromyography (sEMG) will be used to record submental muscle (SbM) activity in healthy participants during a virtual reality (VR) shopping task. This will assess hedonic preferences and respective physiological correlates. In Study 2, motor-evoked potentials (MEPs) from the submental muscle will be elicited using transcranial magnetic stimulation (TMS) in early-stage PD patients, both in the "off-medication" and "on-medication" conditions, following L-Dopa administration. An age-matched control group will be included to compare CB tract excitability between healthy individuals and PD patients.This protocol combines advanced neurophysiological techniques with innovative experimental paradigms to investigate CB tract function as a potential biomarker for reward-related cortical excitability. The findings could offer valuable insights into the neurobiology of dopaminergic dysfunction and contribute to the development of diagnostic and therapeutic strategies for PD.