Aim: Observation of hand or foot flexion-extension movements executed by others evokes in limb-specific spinal motor pathways of the observer a “motor resonant” response (MR) with the same time course and muscular activation pattern as used in the observed movements. Changing the position of the hand (prone to supine) produces the same effects on the timing of both subliminal resonant response during observation and muscular contractions during movement, presumably by a different partitioning of the motor command to flexor and extensor muscles depending on hand kinaesthetic afferences (Borroni et al. 2005). Here we continue this line of investigation by studying the effects of changes in position of the foot, during observation of foot oscillation movements. Methods: Modulation of the H-reflex in the right Soleus muscle was recorded in human observers sitting in a chair with their feet either suspended or in full contact with the ground (n=9 and n=10 respectively). Subjects observed a 1Hz sinusoidal oscillation of the suspended right foot performed by another subject sitting in front of them. Results: In both foot positions, observation induced a significant (p<0.0001) H-reflex modulation which could be fitted by a sinusoidal function with the same period as the observed movement. The common fit of the H-reflex modulations from all subjects was phase-shifted with respect to movement ( by 66° (average 66° ± 15) when the foot was suspended and by 159° (average = 152° ± 41) when it was resting on the ground. Average values are significantly different (p<0.001, Watson-Williams test). Conclusion: With the foot suspended, the time course of MR reflects the temporal relations between muscular activation and the flexion-extension movement at 1Hz. With the foot on the ground, the shift in and its greater variability (p<0.025, Mann-Whitney test on angular distances) may reflect an attempt to reproduce a movement similar but not identical to the observed one. In fact, in this position afferent input informs the observer that the flexion-extension movement cannot be executed.
|Titolo:||Effects of limb position on motor resonance|
|Parole Chiave:||motor resonance ; H-reflex ; movement observation|
|Settore Scientifico Disciplinare:||Settore BIO/09 - Fisiologia|
|Data di pubblicazione:||2006|
|Appare nelle tipologie:||01 - Articolo su periodico|