title: Influence of common synaptic input to motor neurons on the neural drive to muscle in essential tremor.
abstract: Tremor in essential tremor (ET) is generated by pathological oscillations at 4-12 Hz, likely originating at cerebello-thalamo-cortical pathways. However, the way in which tremor is represented in the output of the spinal cord circuitries is largely unknown because of the difficulties in identifying the behavior of individual motor units from tremulous muscles. By using novel methods for the decomposition of multichannel surface EMG, we provide a systematic analysis of the discharge properties of motor units in nine ET patients, with concurrent recordings of EEG activity. This analysis allowed us to infer the contribution of common synaptic inputs to motor neurons in ET. Motor unit short-term synchronization was significantly greater in ET patients than in healthy subjects. Furthermore, the strong association between the degree of synchronization and the peak in coherence between motor unit spike trains at the tremor frequency indicated that the high synchronization levels were generated mainly by common synaptic inputs specifically at the tremor frequency. The coherence between EEG and motor unit spike trains demonstrated the presence of common cortical input to the motor neurons at the tremor frequency. Nonetheless, the strength of this input was uncorrelated to the net common synaptic input at the tremor frequency, suggesting a contribution of spinal afferents or secondary supraspinal pathways in projecting common input at the tremor frequency. These results provide the first systematic analysis of the neural drive to the muscle in ET and elucidate some of its characteristics that determine pathological tremulous muscle activity.
authors.affiliation: Neuroengineering and Cognitive Science Group, Centre for Automation and Robotics, Consejo Superior de Investigaciones Científicas, Arganda del Rey, Spain;
authors.forename: Juan A
authors.initials: JA
authors.lastname: Gallego
authors.affiliation: Department of Neurorehabilitation Engineering, Bernstein Focus Neurotechnology Göttingen, Bernstein Center for Computational Neuroscience, University Medical Center Göttingen, Georg-August University, Göttingen, Germany;
authors.forename: Jakob L
authors.initials: JL
authors.lastname: Dideriksen
authors.affiliation: Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia;
authors.forename: Ales
authors.initials: A
authors.lastname: Holobar
authors.affiliation: Neural Rehabilitation Group, Cajal Institute, Consejo Superior de Investigaciones Científicas, Madrid, Spain;
authors.forename: Jaime
authors.initials: J
authors.lastname: Ibáñez
authors.affiliation: Neural Rehabilitation Group, Cajal Institute, Consejo Superior de Investigaciones Científicas, Madrid, Spain;
authors.forename: José L
authors.initials: JL
authors.lastname: Pons
authors.affiliation: Department of Neurology, College of Physicians and Surgeons, and Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York; and.
authors.forename: Elan D
authors.initials: ED
authors.lastname: Louis
authors.affiliation: Neuroengineering and Cognitive Science Group, Centre for Automation and Robotics, Consejo Superior de Investigaciones Científicas, Arganda del Rey, Spain; Postgraduate Program, Universidade Federal do Espírito Santo, Vitória, Brazil.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Rocon
authors.affiliation: Department of Neurorehabilitation Engineering, Bernstein Focus Neurotechnology Göttingen, Bernstein Center for Computational Neuroscience, University Medical Center Göttingen, Georg-August University, Göttingen, Germany; dario.farina@bccn.uni-goettingen.de.
authors.forename: Dario
authors.initials: D
authors.lastname: Farina
mesh_terms: D000200:Action Potentials; D000368:Aged; D000369:Aged, 80 and over; D004569:Electroencephalography; D004576:Electromyography; D020329:Essential Tremor / Q000503:physiopathology*; D006225:Hand / Q000503:physiopathology; D006801:Humans; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D066191:Sensorimotor Cortex / Q000503:physiopathology*; D013569:Synapses / Q000502:physiology*
keywords: EEG; EMG; coherence; motor neuron; motor unit; pathological tremor