Primary Motor Cortex Activation during Action Observation of Tasks at Different Video Speeds Is Dependent on Movement Task and Muscle Properties.
The aim of the present study was to investigate how the video speed of observed action affects the excitability of the primary motor cortex (M1), as assessed by the size of motor-evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS). Twelve healthy subjects observed a video clip of a person catching a ball (Experiment 1: rapid movement) and another 12 healthy subjects observed a video clip of a person reaching to lift a ball (Experiment 2: slow movement task). We played each video at three different speeds (slow, normal and fast). The stimulus was given at two points of timing in each experiment. These stimulus points were locked to specific frames of the video rather than occurring at specific absolute times, for ease of comparison across different speeds. We recorded MEPs from the first dorsal interosseous muscle (FDI) and abductor digiti minimi muscle (ADM) of the right hand. MEPs were significantly different for different video speeds only in the rapid movement task. MEPs for the rapid movement task were higher when subjects observed an action played at slow speed than normal or fast speed condition. There was no significant change for the slow movement task. Video speed was effective only in the ADM. Moreover, MEPs in the ADM were significantly higher than in the FDI in a rapid movement task under the slow speed condition. Our findings suggest that the M1 becomes more excitable when subjects observe the video clip at the slow speed in a rapid movement, because they could recognize the elements of movement in others. Our results suggest the effects of manipulating the speed of the viewed task on the excitability of the M1 during passive observation differ depending on the type of movement task observed. It is likely that rehabilitation in the clinical setting will be more efficient if the video speed is changed to match the task's characteristics.
Department of Community-based Rehabilitation Sciences, Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical SciencesNagasaki, Japan; Research Fellow of the Japan Society for the Promotion of ScienceTokyo, Japan.
Takefumi
T
Moriuchi
Department of Occupational Therapy, Unit of Physical and Occupational Therapy, Nagasaki University Graduate School of Biomedical Sciences Health Sciences Nagasaki, Japan.
Daiki
D
Matsuda
Department of Community-based Rehabilitation Sciences, Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences Nagasaki, Japan.
Jirou
J
Nakamura
Department of Community-based Rehabilitation Sciences, Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences Nagasaki, Japan.
Takashi
T
Matsuo
Department of Community-based Rehabilitation Sciences, Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences Nagasaki, Japan.
Akira
A
Nakashima
Department of Macroscopic Anatomy, Nagasaki University Graduate School of Biomedical Sciences Nagasaki, Japan.
Keita
K
Nishi
Department of Occupational Therapy, Unit of Physical and Occupational Therapy, Nagasaki University Graduate School of Biomedical Sciences Health Sciences Nagasaki, Japan.
Kengo
K
Fujiwara
Department of Community-based Rehabilitation Sciences, Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences Nagasaki, Japan.
Naoki
N
Iso
Department of Psychiatric Rehabilitation Sciences, Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences Nagasaki, Japan.
Hideyuki
H
Nakane
Department of Community-based Rehabilitation Sciences, Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences Nagasaki, Japan.
Toshio
T
Higashi
action observation; mirror neuron system; motor-evoked potentials; primary motor cortex; slow motion; transcranial magnetic stimulation; video speed