Cortico-spinal embodiment of newly acquired, action-related semantic associations

Background Behavioral and neurophysiological studies indicate that the semantic derivation of the motor skills of a given model (e.g., famous tennis or soccer athlete) modulates the reactivity of arm and leg cortico-spinal representations of an onlooker who performs a categorization task. Information on the possible plastic nature of the sensorimotor mapping of action-related knowledge is still lacking. Objective/hypothesis Here we explored the time course of any cortico-spinal excitability modulation induced by the creation of arbitrary associations between a personal name and tennis- or soccer-related motor skills. Methods We recorded the amplitude of Transcranial Magnetic Stimulation (TMS) Motor Evoked Potentials (MEPs) from arm and leg muscles during a categorization task concerning names that were learned in association with either soccer players, tennis players or control, non-motor, identities (actors). We stimulated the cortico-spinal system and recorded the MEPs at three different time points (0-24-72 h) after the association learning. Results Coherently with previous literature we found a relative dissociation of leg muscles MEPs during reading of soccer-associated personal names with respect to tennis ones. Importantly this modulation was measured only 72 h after having learned the association. This effect was not found in the arm muscle. Conclusion The results suggest that for the process of embodying semantic associations in the motor system to take place, the strength of the association itself needs to rise above some level of consolidation.