title: Alpha band cortico-muscular coherence occurs in healthy individuals during mechanically-induced tremor.
abstract: The present work aimed at investigating the effects of mechanically amplified tremor on cortico-muscular coherence (CMC) in the alpha band. The study of CMC in this specific band is of particular interest because this coherence is usually absent in healthy individuals and it is an aberrant feature in patients affected by pathological tremors; understanding its mechanisms is therefore important. Thirteen healthy volunteers (23±4 years) performed elbow flexor sustained contractions both against a spring load and in isometric conditions at 20% of maximal voluntary isometric contraction (MVC). Spring stiffness was selected to induce instability in the stretch reflex servo loop. 64 EEG channels, surface EMG from the biceps brachii muscle and force were simultaneously recorded. Contractions against the spring resulted in greater fluctuations of the force signal and EMG amplitude compared to isometric conditions (p<.05). During isometric contractions CMC was systematically found in the beta band and sporadically observed in the alpha band. However, during the contractions against the spring load, CMC in the alpha band was observed in 12 out of 13 volunteers. Partial directed coherence (PDC) revealed an increased information flow in the EMG to EEG direction in the alpha band (p<.05). Therefore, coherence in the alpha band between the sensory-motor cortex and the biceps brachii muscle can be systematically induced in healthy individuals by mechanically amplifying tremor. The increased information flow in the EMG to EEG direction may reflect enhanced afferent activity from the muscle spindles. These results may contribute to the understanding of the presence of alpha band CMC in tremor related pathologies by suggesting that the origin of this phenomenon may not only be at cortical level but may also be affected by spinal circuit loops.
authors.affiliation: Department of Movement, Human and Health Sciences, University of Rome Foro Italico, Rome, Italy; School of Public Health, Physiotherapy and Population Science, University College Dublin, Dublin, Ireland.
authors.forename: Francesco
authors.initials: F
authors.lastname: Budini
authors.affiliation: School of Electrical, Electronic and Communications Engineering, University College Dublin, Dublin, Ireland.
authors.forename: Lara M
authors.initials: LM
authors.lastname: McManus
authors.affiliation: Department of Movement, Human and Health Sciences, University of Rome Foro Italico, Rome, Italy.
authors.forename: Marika
authors.initials: M
authors.lastname: Berchicci
authors.affiliation: Department of Movement, Human and Health Sciences, University of Rome Foro Italico, Rome, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Menotti
authors.affiliation: Department of Movement, Human and Health Sciences, University of Rome Foro Italico, Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Macaluso
authors.affiliation: Department of Movement, Human and Health Sciences, University of Rome Foro Italico, Rome, Italy; Neuropsychology Unit, IRCCS Santa Lucia Foundation, Rome, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Di Russo
authors.affiliation: School of Electrical, Electronic and Communications Engineering, University College Dublin, Dublin, Ireland.
authors.forename: Madeleine M
authors.initials: MM
authors.lastname: Lowery
authors.affiliation: School of Public Health, Physiotherapy and Population Science, University College Dublin, Dublin, Ireland.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: De Vito
mesh_terms: D000328:Adult; D004550:Elbow / Q000502:physiology; D004569:Electroencephalography; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D012026:Reflex, Stretch / Q000502:physiology*; D066191:Sensorimotor Cortex / Q000502:physiology*; D014202:Tremor / Q000503:physiopathology; D055815:Young Adult