Inchon Park, M.S.

Well-coordinated behavior between the limbs is one of the remarkable abilities of human beings. Walking, running, and cycling are forms of highly coordinated simple cyclical motion. These kinds of movements require synchronized or alternated motion of the limbs. Bimanual movement is another good example of movements that are highly coordinated. Bimanual movements account for a substantial proportion of our daily life activities such as tying shoelaces, opening bottles, sending a text message and so on. Some difficult bimanual skills require extensive training to reach a high skill level. However, some bimanual motor skills, once acquired, continuously improve even without practice, so-called off-line learning or consolidation. 

A study revealed that a difficult bimanual coordination skill could be easily performed after five minutes of practice when a salient integrated feedback display was provided (e.g., pendulum animation or Lissajous plot); instead of several days of practice. However, after a 15-minute delay from completion of training, participants were unable to perform the trained task without the visual feedback [12]. A recent study in our lab revealed a contradictory finding to the previous study. A newly acquired difficult bimanual skill is resistant to forgetting and is maintained after a certain time delay between the training and retest because of the "offline" consolidation process. Specifically, the trained skill was disrupted by the secondary task after 2-hour delay, but the skill was not degraded by the interference task after 6-hour delay. This finding is consistent with previous studies showing that consolidation will occur with at least a 4-hour delay between training and the retesting session in serial reaction time tasks (SRTT) and discrete aiming tasks [7, 8]. However, the changes in cortical excitability regarding rhythmic bimanual coordination skills are not yet understood. 

Recently, Tunovic et al. (2013) reported distinct changes in corticospinal excitability of the primary motor cortex (M1) following training with different types of sequential movement tasks. There were no significant cortical excitability changes in participants that do not remember the order of trained sequence, but performance was enhanced over wakefulness without additional training. However, a transient decrease in excitability was reported in participants that remember the order of trained task, but the performance was not enhanced. Consequently, they suggested that substantial decreases in critical excitability immediately after motor skill training may be a physiological marker that prevents the consolidation of the motor memory for explicit motor tasks during wakefulness. 

However, in the area of motor control/learning, rhythmic bimanual tasks are often treated as distinct and different from sequential movement tasks for a variety of reasons. The question becomes though: How generalizable is the memory formation processes that have been identified with the SRTT?

The goal of this study is to investigate the changes in cortical excitability of M1 following the learning of a novel bimanual coordination pattern. TMS will be used to probe M1 cortical excitability. The current experiment will link the neural and behavioral levels together and provide a better understanding of the functional role of M1 in learning and memory storage during bimanual skill learning.