Motor excitability during imagination and observation of foot dorsiflexions.

To explore the effects of motor imagery (MI) and action observation (AO) of foot movements on motor excitability. Fifteen healthy subjects were studied at rest, during MI of foot dorsiflexions and during watching a video of foot dorsiflexions. Transcranial magnetic stimulation was used to explore corticospinal and intracortical excitability by comparing amplitudes of motor-evoked potentials during the different conditions. F waves were recorded to test the spinal motoneuronal excitability. MI and AO increased corticospinal excitability, but MI was more effective than AO. During MI, intracortical inhibition was reduced. Intracortical facilitation and spinal motoneuronal excitability remained unchanged. Excitability increases were similar for the right and the left leg when recording from the side the subjects had focused their MI on. However, MI of left foot dorsiflexions did not increase excitability in the right tibial anterior muscle. MI and AO of foot dorsiflexions enhance motor excitability. MI induced a disinhibition in the motor cortex. The lack of excitability increase during MI of contralateral foot movements might be related to the alternating movement pattern during walking. MI and AO effects could support the restitution of motor deficits in neurological diseases with impaired motor excitability.