Bilateral motor control during motor tasks involving the nondominant hand

It is generally thought that fatigue is modulated during prolonged exhaustive motor tasks by the bilateral motor cortex. It remains unclear, however, how fatigue is modulated during motor tasks and how information about fatigue affects motor cortex activities in healthy humans. These results may help explain why fatigue is so prevalent in patients with neurological disorders. The purpose of the present study was to investigate the time course of oxygenation of the ipsilateral motor cortex during an exhaustive pinching task. Seven healthy right-handed subjects participated in the study. Near-infrared spectroscopy over the bilateral motor cortices was used to measure activity throughout the pinching task. Subjects performed a sustained maximal voluntary contraction of 50-60% with their left hands until voluntary exhaustion was reached. After the start of the motor task, oxygenation to the contralateral motor cortex increased significantly compared with the resting value (p<0.05). However, with the passage of time, it decreased significantly compared with the resting value (p<0.05). In addition, oxygenation of the ipsilateral motor cortex significantly increased after the start of the motor task, and then decreased significantly at voluntary exhaustion compared with the resting value (p<0.05). These results suggest an interaction between the bilateral motor cortices during motor tasks.