Excitability Changes in the Human Primary Motor Cortex During Observation with Motor Imagery of Chopstick Use

[Purpose] The aim of this study was to investigate whether the performance of a combination of observation and motor imagery of chopstick use (complex task) increased corticospinal excitability more than the performance of observation alone. [Subjects and Methods] We recruited 10 healthy subjects with no history of neurological diseases. Corticospinal excitability was assessed with the participants seated in front of a computer screen performing three tasks: (1) control, the subjects were instructed to relax; (2) OBS, the subjects were told to observe an action depicted in the video, and (3) OBS + IMG, the subjects were told to imagine performing an action depicted in a video. During tasks (2) and (3), a video was displayed on the computer screen showing the hand of a male subject using chopsticks to move small items of food from one dish to another (first person perspective). Imagery was performed kinesthetically. [Results] The MEP amplitude in the first dorsal interosseous was significantly increased during OBS+IMG relative to that in the control condition, but not that in the OBS condition. The MEP amplitude in the thenar muscles was significantly different between OBS and OBS+IMG. [Conclusion] These results suggest that the combination of observation and motor imagery of a complex task may be more effective than observation alone for motor rehabilitation purposes.