title: Dynamical entrainment of corticospinal excitability during rhythmic movement observation: a Transcranial Magnetic Stimulation study.
abstract: Spontaneous modulations of corticospinal excitability during action observation have been interpreted as evidence for the activation of internal motor representations equivalent to the observed action. Alternatively or complementary to this perspective, growing evidence shows that motor activity during observation of rhythmic movements can be modulated by direct visuomotor couplings and dynamical entrainment. In-phase and anti-phase entrainment spontaneously occur, characterized by cyclic movements proceeding simultaneously in the same (in-phase) or opposite (anti-phase) direction. Here we investigate corticospinal excitability during the observation of vertical oscillations of an index finger using Transcranial Magnetic Stimulation (TMS). Motor-evoked potentials (MEPs) were recorded from participants' flexor and extensor muscles of the right index finger, placed in either a maximal steady flexion or extension position, with stimulations delivered at maximal flexion, maximal extension or mid-trajectory of the observed finger oscillations. Consistent with the occurrence of dynamical motor entrainment, increased and decreased MEP responses - suggesting the facilitation of stable in-phase and anti-phase relations but not an unstable 90° phase relation - were found in participants' flexors. Anti-phase motor facilitation contrasts with the activation of internal motor representation as it involves activity in the motor system opposite from activity required for the execution of the observed movement. These findings demonstrate the relevance of dynamical entrainment theories and methods for understanding spontaneous motor activity in the brain during action observation and the mechanisms underpinning coordinated movements during social interaction.
authors.affiliation: The MARCS Institute for Brain, Behaviour and Development, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: Manuel
authors.identifier: 0000-0001-5772-2061
authors.initials: M
authors.lastname: Varlet
authors.affiliation: The MARCS Institute for Brain, Behaviour and Development, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.|Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Novembre
authors.affiliation: The MARCS Institute for Brain, Behaviour and Development, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Keller
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor; D005260:Female; D005385:Fingers / Q000502:physiology; D006801:Humans; D008297:Male; D009068:Movement; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D010507:Periodicity; D011712:Pyramidal Tracts / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D014796:Visual Perception
keywords: action observation; dynamical systems; entrainment; motor evoked potential