title: Abnormal corticomuscular coherence is associated with the small amplitude cortical myoclonus in Parkinson's disease.
abstract: Coherence is the degree of time-locked correlation between two signals as a function of frequency. The purpose of this study was to test the following hypotheses: (1) corticomuscular coherence is abnormally increased in those Parkinson's disease (PD) patients with small amplitude cortical myoclonus, and (2) corticomuscular coherence peaks around the time of the myoclonus electromyographic (EMG) discharge. We studied Parkinson's disease patients with and without myoclonus and controls. The data were digitally collected and processed off-line with EMG rectification, creation of 511-msec epochs, Fast-Fourier transform, and coherence analysis. In the 12 to 30 Hz frequency band, but not at 30 to 60 Hz or above, coherence peaks were observed in the PD subjects with myoclonus that were significantly greater than in the control subjects (P < 0.001) and in PD subjects without myoclonus (P < 0.001). The abnormal coherence values are evidence for abnormal rhythmic activity in cortical motor areas in those Parkinson's disease patients with myoclonus. In combination with previous findings on back-averaging, our results show that this myoclonus occurs when neuronal populations are driven to an extreme amount of synchronous activity with higher corticomuscular coherence values. These results have mechanistic implications for cortical dysfunction in Parkinson's disease and for cortical myoclonus in general.
authors.affiliation: Department of Neurology, Mayo Clinic Scottsdale, Scottsdale, Arizona 85259, USA. jcaviness@mayo.edu
authors.forename: John N
authors.initials: JN
authors.lastname: Caviness
authors.forename: Charles H
authors.initials: CH
authors.lastname: Adler
authors.forename: Marwan N
authors.initials: MN
authors.lastname: Sabbagh
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Connor
authors.forename: Jose L
authors.initials: JL
authors.lastname: Hernandez
authors.forename: Terrence D
authors.initials: TD
authors.lastname: Lagerlund
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D004569:Electroencephalography / Q000379:methods; D004576:Electromyography / Q000379:methods; D005583:Fourier Analysis; D006801:Humans; D009044:Motor Cortex / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009207:Myoclonus / Q000209:etiology*; D010300:Parkinson Disease / Q000503:physiopathology*; D011569:Psychiatric Status Rating Scales; D013997:Time Factors