title: Direct mapping rather than motor prediction subserves modulation of corticospinal excitability during observation of actions in real time.
abstract: Motor facilitation refers to the specific increment in corticospinal excitability (CSE) elicited by the observation of actions performed by others. To date, the precise nature of the mechanism at the basis of this phenomenon is unknown. One possibility is that motor facilitation is driven by a predictive process reminiscent of the role of forward models in motor control. Alternatively, motor facilitation may result from a model-free mechanism by which the basic elements of the observed action are directly mapped onto their cortical representations. Our study was designed to discern these alternatives. To this aim, we recorded the time course of CSE for the first dorsal interosseous (FDI) and the abductor digiti minimi (ADM) during observation of three grasping actions in real time, two of which strongly diverged in kinematics from their natural (invariant) form. Although artificially slow movements used in most action observation studies might enhance the observer's discrimination performance, the use of videos in real time is crucial to maintain the time course of CSE within the physiological range of daily actions. CSE was measured at 4 time points within a 240-ms window that best captured the kinematic divergence from the invariant form. Our results show that CSE of the FDI, not the ADM, closely follows the functional role of the muscle despite the mismatch between the natural and the divergent kinematics. We propose that motor facilitation during observation of actions performed in real time reflects the model-free coding of perceived movement following a direct mapping mechanism.
authors: Institute of Physiology and Biophysics Bernardo Houssay (IFIBIO Houssay), Department of Physiology and Biophysics, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina; and.
authors: Nicolas
authors: N
authors: Gueugneau
authors: Institute of Physiology and Biophysics Bernardo Houssay (IFIBIO Houssay), Department of Physiology and Biophysics, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina; and.
authors: Sofia I
authors: SI
authors: Mc Cabe
authors: Institute of Physiology and Biophysics Bernardo Houssay (IFIBIO Houssay), Department of Physiology and Biophysics, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina; and.
authors: Jorge I
authors: JI
authors: Villalta
authors: Department of Psychology, University of California, Santa Barbara, California.
authors: Scott T
authors: ST
authors: Grafton
authors: Institute of Physiology and Biophysics Bernardo Houssay (IFIBIO Houssay), Department of Physiology and Biophysics, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina; and vdellamaggiore@fmed.uba.ar.
authors: Valeria
authors: V
authors: Della-Maggiore
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D001931:Brain Mapping; D004192:Discrimination, Psychological; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D007092:Imagination; D008297:Male; D009068:Movement; D018482:Muscle, Skeletal; D010775:Photic Stimulation; D011712:Pyramidal Tracts / Q000166:cytology / Q000502:physiology*; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: action observation; corticospinal excitability; direct mapping; forward models; motor facilitation; motor prediction