title: Thalamomuscular coherence in essential tremor: hen or egg in the emergence of tremor?
abstract: Thalamomuscular coherence in essential tremor (ET) has consistently been detected in numerous neurophysiological studies. Thereby, spatial properties of coherence indicate a differentiated, somatotopic organization; so far, however, little attention has been paid to temporal aspects of this interdependency. Further insight into the relationship between tremor onset and the onset of coherence could pave the way to more efficient deep brain stimulation (DBS) algorithms for tremor. We studied 10 severely affected ET patients (six females, four males) during surgery for DBS-electrode implantation and simultaneously recorded local field potentials (LFPs) and surface electromyographic signals (EMGs) from the extensor and flexor muscles of the contralateral forearm during its elevation. The temporal relationship between the onset of significant wavelet cross spectrum (WCS) and tremor onset was determined. Moreover, we examined the influence of electrode location within one recording depth on this latency and the coincidence of coherence and tremor for depths with strong overall coherence ("tremor clusters") and those without. Data analysis revealed tremor onset occurring 220 ± 460 ms before the start of significant LFP-EMG coherence. Furthermore, we could detect an anterolateral gradient of WCS onset within one recording depth. Finally, the coincidence of tremor and coherence was significantly higher in tremor clusters. We conclude that tremor onset precedes the beginning of coherence. Besides, within one recording depth there is a spread of the tremor signal. This reflects the importance of somatosensory feedback for ET and questions the suitability of thalamomuscular coherence as a biomarker for "closed-loop" DBS systems to prevent tremor emergence.
authors.affiliation: Department of Neurology and david.pedrosa@uk-koeln.de.
authors.forename: David J
authors.identifier: http://orcid.org/0000-0002-5403-1959
authors.initials: DJ
authors.lastname: Pedrosa
authors.affiliation: Department of Neurology and.
authors.forename: Eva-Lotte
authors.identifier: http://orcid.org/0000-0002-1274-6155
authors.initials: EL
authors.lastname: Quatuor
authors.affiliation: Department of Neurology and.
authors.forename: Christiane
authors.initials: C
authors.lastname: Reck
authors.affiliation: Department of Neurology and.
authors.forename: K Amande M
authors.initials: KA
authors.lastname: Pauls
authors.affiliation: Department of Neurology and.
authors.forename: Carlo A
authors.initials: CA
authors.lastname: Huber
authors.affiliation: Department of Stereotactic and Functional Neurosurgery, University Hospital Cologne, 50924 Cologne, Germany.
authors.forename: Veerle
authors.initials: V
authors.lastname: Visser-Vandewalle
authors.affiliation: Department of Neurology and.
authors.forename: Lars
authors.initials: L
authors.lastname: Timmermann
mesh_terms: D000368:Aged; D046690:Deep Brain Stimulation / Q000295:instrumentation / Q000379:methods*; D004567:Electrodes, Implanted; D020329:Essential Tremor / Q000175:diagnosis / Q000503:physiopathology* / Q000628:therapy*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000295:instrumentation / Q000379:methods*; D018482:Muscle, Skeletal / Q000502:physiology*; D013788:Thalamus / Q000502:physiology*
keywords: deep brain stimulation; essential tremor; neurophysiology; thalamus; wavelet cross-spectrum