This study aimed to compare the excitability of spinal motor neurons among AO + MI, AO, and MI conditions using the F-wave.
Seventeen healthy volunteers were participated in this study. To apply AO and MI to rehabilitation for person with a stroke, a non-dominant hand that is not usually used for AO and MI tasks was adopted. All of them were determined to be right-handed with Edinburgh Handedness Inventory. Before the F-wave recording, cyclic left thumb opposition movements at a frequency of 1 Hz were video-recorded using an iPad. The F-wave recordings were performed under four experimental conditions termed Rest, AO, MI, and AO + MI. Firstly, in the Rest condition, the F-wave was recorded during relaxation for 1 min to determine the baseline excitability of spinal motor neurons. In the AO condition, the F-wave was recorded while the participants viewed the previously recorded video for 1 min. The size and position of the hand image displayed on the iPad were adjusted to the size and position of their hand. Additionally, in the AO condition, the participants were instructed not to imagine the hand movements displayed on the iPad. In the MI condition, the F-wave was recorded while the participants imagined the cyclic left thumb opposition movements at 1 Hz with metronome cues for 1min. The participants were instructed to perform kinesthetic imagery. In the AO + MI condition, the participants observed the same video as used in the AO condition, and they imagined the movements displayed on the iPad. The participants were then instructed to perform kinesthetic imagery as the MI condition. To avoid the order effect, the AO, MI, and AO + MI conditions were randomly performed. Recorded F-wave data in each condition were analyzed with respect to persistence and the F/M amplitude ratio.
The F/M amplitude ratio and persistence during the AO, MI, and AO + MI conditions were significantly higher than that at the Rest condition. Additionally, the F/M amplitude ratio during the AO + MI condition was significantly higher than that at the AO condition. The F/M amplitude ratio during the MI condition was also significantly higher than that at AO condition.
These results suggest that AO + MI facilitates the excitability of spinal motor neurons compared to AO alone. Whereas the facilitation effect of AO + MI on the excitability of spinal motor neurons is the same as that of MI alone. Also, MI facilitates the excitability of spinal motor neurons compared to AO alone.
AO + MI may be more effective as a rehabilitation method than AO alone. However, the effect of AO + MI is similar with the MI alone.
Action observation
F-wave
