Author(s): KITAMURA, M., ISHIKURA, T., OGISO, G., KAMIBAYASHI, K., Institution: DOSHISHA UNIVERSITY, Country: JAPAN, Abstract-ID: 1504

INTRODUCTION:
Observing others actions facilitates the corticospinal excitability (CSE) of the muscles associated with the observed actions [1]. A previous study [2] indicated that motor-related brain areas are strongly activated when observers observe movements that they have repeatedly practiced and are already skilled in, compared to when they observe movements they have not experienced. The previous study only investigated voluntary movements with complex actions (e.g., dancing) and did not analyze semi-automatic rhythmic movements (e.g., walking). Thus, it is unclear how the observers motor system is activated by observing unusual walking patterns that they have not experienced before. Therefore, we aimed to investigate changes in CSE by observing walking in a split-belt condition with different left and right treadmill belt speeds, which the observers had not experienced before. When humans are exposed to the split-belt condition, their gait becomes asymmetric at the initial period of the split-belt condition but approaches symmetry after several minutes [3]. Thus, we examined CSE during the observation of the asymmetric and symmetric walking at the initial and late periods of the split-belt condition, respectively.
METHODS:
Fifteen healthy adults participated in the study. From the video of lower limb movements during walking captured from the actors left side, three different video clips were created: 10 seconds during walking in the tied condition (belt speeds: 1.25 m/s), as well as the initial 10 seconds (initial period) and last 10 seconds (late period) during a 10-minute walking in the split-belt condition (left and right belt speeds: 1.0 and 1.5 m/s, respectively). The video clips showed that the actors step lengths were almost symmetric in the tied condition and late period of the split-belt condition, but largely asymmetric in the initial period of the split-belt condition. The participants observed a fixation cross (control condition) and three different video clips that were presented randomly on a monitor. The motor-evoked potential (MEP) of the left tibialis anterior muscle was recorded by delivering transcranial magnetic stimulation to the right primary motor cortex during the observation.
RESULTS:
The MEP amplitude during the observation of walking in the tied condition and the late period of the split-belt condition was significantly larger than that in the control condition. However, no significant difference in the MEP amplitude was observed between the control condition and the initial period of the split-belt condition.
CONCLUSION:
These results suggest that when observing semi-automatic movements like walking, observation of symmetric walking, similar to observers walking, facilitates CSE. However, observation of asymmetric walking, which observers have not experienced, does not appear to facilitate CSE.

[1] Fadiga et al. 1995., J. Neurophysiol.
[2] Calvo-Merino et al. 2005., Cereb. Cortex
[3] Reisman et al. 2005., J. Neurophysiol.