Effects of motor imagery on intermanual transfer: a near-infrared spectroscopy and behavioural study

Intermanual transfer is the ability that previous studies by one limb promote the later learning by the other limb. This ability has been demonstrated in various effectors and types of training. Motor imagery, the mental simulation of motor execution, is believed to be strongly associated with the cognitive aspects of motor execution, and the pattern of brain activity during motor imagery is similar to that of motor execution, although the activation pattern is smaller, and the level is lower. If the cognitive component of motor execution strongly contributes to transfer, the training effect of motor imagery would be expected to transfer to the contralateral limb. In the present study, we used the tapping sequence paradigm to evaluate the occurrence of intermanual transfer through motor imagery and to compare differences of transfer effects to motor execution learning. We divided participants into three groups: an execution group, a motor imagery group and a no-training control group. Before and after a nondominant left hand training session, ipsilateral hand tests were conducted. After the post-test, a contralateral right-hand test was also conducted. In order to investigate the relationship between transfer effect and neural activation during the learning phase, we measured motor-related brain area activity using near-infrared spectroscopy (NIRS). Execution was effective especially for trained movement, imagery was effective for both trained movement and intermanual transfer. Brain activity suggesting predictive transfer differed between two groups, suggesting that motor execution and motor imagery training have different behavioural effects and neural contributions.