Imagining stumbling inhibits motor-evoked potentials in the soleus muscle

The purpose of this study was to investigate the cortical influences on the soleus and tibialis anterior muscles while the subject imagined stumbling. While standing, 7 healthy subjects imagined the following situations: stumbling by either the right or left leg stepping into an obstacle during walking, or a sudden backward sway of the body while in stance. Motor-evoked potentials (MEPs) in the soleus muscle and in the tibialis anterior muscle, along with soleus H-reflexes, were recorded from the left lower extremity. MEP amplitudes in the soleus muscle significantly decreased during the imagined stumbling. In contrast, there was no significant change in the MEP amplitudes in the tibialis anterior muscle or in the soleus H-reflex amplitudes. These results indicate that imagining stumbling modulates the cortical influence to the soleus muscle. The modulation may be related to cortical inhibition of the tonic muscle in order for voluntary movement to overcome antigravity postural mechanisms.