Coupling Phenomenon Observed with NIRS in Bimanual Operation

Coupling Phenomenon Observed with NIRS in Bimanual Operation

  In this paper, the activation of left and right motor cortex areas during bimanual and unimanual operations is investigated by using a near-infrared spectroscopy (NIRS), EGT-4000 Optical Topography System made by Hitachi Medical Corporation, Japan. It is found that only left or right side of the motor cortex area is active when a subject"s contralateral hand (or fingers of contralateral hand or contralateral arm) is moving in a slow or normal speed (i.e. a speed which is slower than or the same to the finger/hand/ arm moving speed in his/her dairy life), which coincides with previous research results found in literature. The most important discovery in this investigation is that the other side of the motor cortex area, i.e. the ipsilateral motor cortex area which is inactive for the low speed movement in unimanual operations becomes active when the movement is accelerated to a certain speed, which is much higher than finger/hand/arm moving speed in his/her dairy life and less than the speed limitation of his/her operation. This result reveals that the coupling between left and right motor cortex areas is the reason why the bimanual operation (two hands movement) effects with each other. For each subject participated in this research, a higher moving speed in bimanual operation results in more active in both sides of the motor cortex area. And the threshold speed with which the motor cortex area becomes much more active depends on the operation skill of the subject. More skilled the operator is, higher the threshold speed is.