title: Cortical correlates of the basic and first harmonic frequency of Parkinsonian tremor.
abstract: OBJECTIVE
  It has been hypothesized that the basic and first harmonic frequency of Parkinsonian tremor are somewhat independent oscillations the biological basis of which remains unclear.
  
  
  METHODS
  We recorded 64-channel EEG in parallel with EMG of the forearm muscles most affected by rest tremor in 21 PD patients. EMG power spectrum, corticomuscular coherence spectra and EEG power spectra for each EEG electrode were calculated. The dynamics of the coherence and relative EMG and EEG power at the basic (tremor) frequency were calculated by a sliding, overlapping window analysis. Corticomuscular delays and direction of interaction were analysed by the maximizing coherence method for narrow band signals.
  
  
  RESULTS
  The contralateral EEG electrodes with maximal coherence were different for the basic and first harmonic frequency. The dynamical coherence curves showed non-parallel time courses for the two frequencies. The mean EEG-EMG and EMG-EEG delays were all around 15-20ms but significantly longer for the first harmonic than for the basic frequency.
  
  
  CONCLUSIONS
  Our data indicate different cortical representations and corticomuscular interaction of the basic and first harmonic frequencies of Parkinsonian tremor.
  
  
  CONCLUSIONS
  Separate central generators seem to contribute to the tremor via different pathways. Further studies on this complex tremor network are warranted.
authors.affiliation: Department of Neurology, University of Kiel, Schittenhelmstr. 10, 24105 Kiel, Germany. j.raethjen@neurologie.uni-kiel.de
authors.forename: Jan
authors.initials: J
authors.lastname: Raethjen
authors.forename: R B
authors.initials: RB
authors.lastname: Govindan
authors.forename: M
authors.initials: M
authors.lastname: Muthuraman
authors.forename: Florian
authors.initials: F
authors.lastname: Kopper
authors.forename: Jens
authors.initials: J
authors.lastname: Volkmann
authors.forename: Günther
authors.initials: G
authors.lastname: Deuschl
mesh_terms: D000328:Adult; D000368:Aged; D002540:Cerebral Cortex / Q000503:physiopathology*; D004569:Electroencephalography; D004576:Electromyography; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D010300:Parkinson Disease / Q000503:physiopathology*; D012815:Signal Processing, Computer-Assisted; D014202:Tremor / Q000503:physiopathology*