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Abstract:
Brain imaging studies have reported activation in motor
structures not only during overt motor behavior but also during
tasks such as mental rotation. We tested the hypothesis that
primary motor cortex is involved in mental rotation by using single
pulse transcranial magnetic stimulation (TMS). Single pulse TMS
(120% of each participant's motor threshold) was delivered to the
primary motor representation of the right hand while participants
performed mental rotation of pictures of hands. The main behavioral
measure was the time to report verbally whether the stimulus was a
left or right hand. Response times were slower when the pulse was
delivered at 650 ms but not at 400 ms after stimulus onset,
relative to sham stimulation. The increase in response times was
constant across rotations. This suggests that stimulation affects
the time to begin the motor aspect of the task rather than the
speed of mental rotation per se (measured in ms/degree). All in
all, these results show that primary motor cortex is involved in
the mental rotation of hands and that its recruitment occurs
relatively late in the task.
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