Instantaneous-Frequency EEG Microstate Dynamics Stratify Motor Subtypes in Parkinson's Disease

Parkinson's disease manifests in two main motor subtypes: postural-instability/gait-difficulty (PIGD) and tremor-dominant (TD), but objective electrophysiological markers for distinguishing them are lacking. Researchers analyzed data from 28 healthy individuals and 97 Parkinson's disease patients (50 with PIGD, 47 with TD) using resting-state EEG measurements. Using instantaneous-frequency analysis and a hidden Markov model, they identified three recurring microstates. One microstate showed systematic differences between groups: its dwell time, occupancy, and self-transition probability increased from healthy controls through TD to PIGD patients. The difference in dwell time between healthy controls and PIGD patients was large (Hedges' g=1.06). These dynamic indices distinguished between subtypes independently of disease severity or medication dose. This approach offers an objective EEG marker for distinguishing motor subtypes of Parkinson's disease.