title: Intermittent bilateral coherence in physiological and essential hand tremor.
abstract: To investigate the prevalence and the temporal structure of bilateral coherence in physiological (PT) and essential (ET) hand tremor.
  
  
  
  Triaxial accelerometric recordings from both hands in 30 healthy subjects and 34 ET patients were analyzed using spectral coherence and wavelet coherence methods. In 12 additional healthy subjects, the relation between the hand tremor and the chest wall acceleration was evaluated using partial coherence analysis.
  
  
  
  The majority of both PT and ET subjects displayed significant bilateral coherence. While in PT, bilateral coherence was most frequently found in resting hand position (97% of subjects), in ET the prevalence was comparable for resting (54%) and postural (49%-57%) positions. In both PT and ET, epochs of strong coherence lasting several to a dozen seconds were separated by intervals of insignificant coherence. In PT, bilateral coherence at the main tremor frequency (8-12Hz) was coupled with the ballistocardiac rhythm.
  
  
  
  The oscillations of the two hands are intermittently synchronized in both PT and ET. We propose that in postural PT, bilateral coherence at the main tremor frequency arises from transient simultaneous entrainment of the left and right hand oscillations to ballistocardiac forcing.
  
  
  
  Bilateral coherence of hand kinematics provides a sensitive measure of synchronizing influences on the left and right tremor oscillators.
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic; Department of Neurology, First Faculty of Medicine, Charles University in Prague, Czech Republic.
authors.forename: Soma
authors.initials: S
authors.lastname: Chakraborty
authors.affiliation: Department of Neurology, First Faculty of Medicine, Charles University in Prague, Czech Republic.
authors.forename: Jana
authors.initials: J
authors.lastname: Kopecká
authors.affiliation: Department of Neurology, First Faculty of Medicine, Charles University in Prague, Czech Republic; Institute of Information Theory and Automation, Czech Academy of Sciences, Prague, Czech Republic.
authors.forename: Otakar
authors.initials: O
authors.lastname: Šprdlík
authors.affiliation: Department of Neurology, First Faculty of Medicine, Charles University in Prague, Czech Republic.
authors.forename: Martina
authors.initials: M
authors.lastname: Hoskovcová
authors.affiliation: Department of Neurology, First Faculty of Medicine, Charles University in Prague, Czech Republic.
authors.forename: Olga
authors.initials: O
authors.lastname: Ulmanová
authors.affiliation: Department of Neurology, First Faculty of Medicine, Charles University in Prague, Czech Republic. Electronic address: eruzi@lf1.cuni.cz.
authors.forename: Evžen
authors.initials: E
authors.lastname: Růžička
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic; Institute of Biophysics and Informatics, First Faculty of Medicine, Charles University in Prague, Czech Republic. Electronic address: zapotocky@biomed.cas.cz.
authors.forename: Martin
authors.initials: M
authors.lastname: Zapotocky
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D004576:Electromyography; D020329:Essential Tremor / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality; D006225:Hand / Q000294:innervation / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D014202:Tremor / Q000503:physiopathology*
keywords: Accelerometry; Ballistocardiac impulse; Bilateral coupling; Coherence; Essential tremor; Physiological tremor; Wavelet analysis