title: Increased SMA-M1 coherence in Parkinson's disease - Pathophysiology or compensation?
abstract: Parkinson's disease (PD) is a common neurodegenerative disorder owing to loss of dopaminergic cells. Akinesia - one of the core symptoms of PD - is associated with exaggerated oscillations at beta frequency (13-30 Hz) within the subthalamic nucleus (STN). Thus, enhanced oscillations below 30 Hz are assumed to represent a pathophysiological marker of PD. However, recent data suggest that OFF medication exaggerated beta oscillations within basal ganglia (BG) cortical networks may serve for the compensation of BG dysfunctions. The STN is functionally connected to mesial prefrontal areas like the supplementary motor area (SMA). But, it is still not fully understood how enhanced beta oscillations within the BG exert dominance over the primary motor cortex (M1) thereby yielding motor impairment. The present study, therefore, investigates the effect of dopaminergic state on SMA-M1 functional connectivity using Magnetoencephalography (MEG). MEG data were recorded in 7 patients suffering from PD with preponderance of akinesia during isometric contraction of the right forearm and during rest. Coherence as a measure of functional connectivity between M1 and SMA was calculated OFF and ON medication and correlated with the motor part of the Unified Parkinson's Disease Rating Scale (UPDRS III) and with disease duration. During rest a significant positive correlation between disease duration and SMA-M1 coherence was found ON but not OFF medication. Conversely, during isometric contraction SMA-M1 coherence and UPDRS III were inversely correlated OFF but not ON medication explaining more than 80% of variance. The results favor the hypothesis that OFF medication exaggerated cortical coherence at beta frequency represents a compensatory mechanism rather than a pathophysiological marker per se.
authors.affiliation: Heinrich-Heine University Duesseldorf, Medical Faculty, Institute of Clinical Neuroscience and Medical Psychology, 40225 Duesseldorf, Germany. bettina.pollok@uni-duesseldorf.de
authors.forename: Bettina
authors.initials: B
authors.lastname: Pollok
authors.forename: Daniel
authors.initials: D
authors.lastname: Kamp
authors.forename: Markus
authors.initials: M
authors.lastname: Butz
authors.forename: Lars
authors.initials: L
authors.lastname: Wojtecki
authors.forename: Lars
authors.initials: L
authors.lastname: Timmermann
authors.forename: Martin
authors.initials: M
authors.lastname: Südmeyer
authors.forename: Vanessa
authors.initials: V
authors.lastname: Krause
authors.forename: Alfons
authors.initials: A
authors.lastname: Schnitzler
mesh_terms: D000368:Aged; D001479:Basal Ganglia / Q000503:physiopathology; D001611:Beta Rhythm / Q000502:physiology*; D001931:Brain Mapping; D004569:Electroencephalography; D004576:Electromyography; D005260:Female; D006801:Humans; D016014:Linear Models; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D010300:Parkinson Disease / Q000473:pathology* / Q000503:physiopathology*; D012720:Severity of Illness Index; D020531:Subthalamic Nucleus / Q000503:physiopathology*
keywords: ANOVA; Analysis of variance; BA; BG; Basal ganglia; Brodmann area; Coherence; Coupling; DICS; Dynamic Imaging of Coherent Sources; EMG; Electromyography; FFT; Fast Fourier transform; Functional magnetic resonance imaging; Levodopa; M1; MEG; MRI; Magnetic resonance imaging; Magnetoencephalography; Motor cortex; Network; Oscillations; PD; PMC; Parkinson's disease; Premotor cortex; Primary motor cortex; SMA; STN; Subthalamic nucleus; Supplementary motor area; UPDRS; Unified Parkinson's Disease Rating Scale; fMRI