title: Corticospinal facilitation during observation of graspable objects: a transcranial magnetic stimulation study.
abstract: In 1979, Gibson first advanced the idea that the sight of graspable objects automatically activates in the observer the repertoire of actions necessary to interact with them, even in the absence of any intention to act ("affordance effect"). The neurophysiological substrate of this effect was later identified in a class of bimodal neurons, the so-called "canonical" neurons, located within monkey premotor cortex. In humans, even if different behavioral studies supported the existence of affordance effect, neurophysiological investigations exploring its neural substrates showed contradictory results. Here, by means of Transcranial Magnetic Stimulation (TMS), we explored the time-course of the "affordance effect" elicited by the observation of everyday-life graspable objects on motor cortex of resting observers. We recorded motor evoked potentials (MEP) from three intrinsic hand muscles (two "synergic" for grasping, OP and FDI and one "neutral", ADM). We found that objects' vision determined an increased excitability at 120 milliseconds after their presentation. Moreover, this modulation was proved to be specific to the cortical representations of synergic muscles. From an evolutionary perspective, this timing perfectly fits with a fast recruitment of the motor system aimed at rapidly and accurately choosing the appropriate motor plans in a competitive environment filled with different opportunities.
authors.affiliation: Department of Biomedical Sciences and Advanced Therapies, Section of Human Physiology, University of Ferrara, Ferrara, Italy. michele.tfr@gmail.com
authors.forename: Michele
authors.initials: M
authors.lastname: Franca
authors.forename: Luca
authors.initials: L
authors.lastname: Turella
authors.forename: Rosario
authors.initials: R
authors.lastname: Canto
authors.forename: Nicola
authors.initials: N
authors.lastname: Brunelli
authors.forename: Luisa
authors.initials: L
authors.lastname: Allione
authors.forename: Nico Golfré
authors.initials: NG
authors.lastname: Andreasi
authors.forename: Marianna
authors.initials: M
authors.lastname: Desantis
authors.forename: Daniele
authors.initials: D
authors.lastname: Marzoli
authors.forename: Luciano
authors.initials: L
authors.lastname: Fadiga
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006225:Hand / Q000502:physiology; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000473:pathology*; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult