POSTURAL MOTOR RESONANCE: A NEW FUNCTION OF THE MIRROR NEURON SYSTEM

F. Bolzoni¹, B. Montanari², V. Farinelli³, P. Adamo², F. Temporiti^2,1, R. Fesce¹, R. Gatti^2,1

¹Humanitas University, Department of Biomedical Sciences, Milano, Italy, ²IRCCS Humanitas Clinical and Research Center, Physiotherapy Unit, Milano, Italy, ³Università degli Studi di Milano, Human Physiology Section of the Department of Pathophysiology and Transplantation, Milano, Italy

Background: Motor resonance is described as a form of implicit motor perception evoked when observing movements performed by others. The observer nervous system “reflects” the observed action by increasing the activity of brain areas involved in performing that same movement. Mirror Neurons (MNs) constitute the neural substrate that drives the motor resonance as these neurons fire both when a subject moves and when a subject observes an individual performing the same motor act. So far, MNS has been described as reflecting the visible movements (i.e. focal), de facto suggesting that the MNS responds to visible, but not non visible (i.e. postural) components. This would be surprising, as any motor act requires a well-tailored dialogue between the motor areas involved in producing the focal movement, and those responsible for the related postural control.

Purpose: To investigate the existence of a “postural motor resonance” that reflects more than the focal movement component.

Methods: In 20 healthy subjects, soleus corticospinal excitability was assessed by eliciting the H-reflex during the observation of three different videos, corresponding to three experimental conditions (“Chest pass”, “Standing” and “Sitting”) where Soleus has different postural roles ("Chest pass" vs. "Standing") or no role ("Sitting"). Thus, we tested the excitability of a muscle involved in the postural control while observing an action in which such muscle did not produce the focal movement.

Results: The H-reflex evoked during the observation of the Chest pass was higher than the H-reflex evoked during the control condition, while the observation of standing did not produce any evident modulation of the H-reflex amplitude. Statistical analysis confirmed that the H-reflex amplitude was significantly greater in the “Chest pass” condition compared to the “Sitting” and “Standing” conditions. No significant difference was found between “Sitting” and “Standing” conditions.

Conclusions: A possible explanation for the described H-reflex modulation during the “Chest pass” condition, is that MNs aimed at maintaining the standing position by counteracting the perturbation caused by the focal movement while reflecting the observed action also reflect the associated postural component. The most intriguing novelty is that the postural component of an observed action evokes motor resonance even though it is not visually evident.

Implications: The possibility of evoking postural resonance through the MNS points to a novel possible role of mirror neurons in motor recovery.

Funding acknowledgements: The authors did not receive any funding.

Keywords:
Mirror neurons
Postural control
H-reflex modulation

Topics:
Neurology

Did this work require ethics approval? Yes

Institution: IRCCS Humanitas Clinical and Research Center

Committee: Internal Ethical Committee of Humanitas Clinical and Research Center

Ethics number: OMP2022