Time-source of neural plasticity in complex bimanual coordinative tasks: Juggling.

Brain plasticity is especially stimulated by complex bimanual tasks, because, as for juggling, they require simultaneous control of multiple movements, high level of bimanual coordination, balance and sustained swapping attention to multiple objects interacting with both hands. Neuroimaging studies on jugglers showed changes in white and grey matter after juggling training, while the very few electroencephalographic (EEG) studies showed changes in the frequency domain. However, no study has focused on the fine temporal brain activations during a bimanual coordinative task in ecological settings. We aimed at understanding the neural correlates of juggling tasks comparing expert jugglers to non-jugglers. Both groups performed two juggling tasks with increasing difficulty (1-ball fountain and 2-ball shower in non-jugglers, 2- and 3-ball shower in expert jugglers), while the EEG was recorded. This design allowed to compare brain activities related to increasing task difficulty within the same group, and the two groups on the same task. The movement-related cortical potentials (MRCPs) for each task were segmented into epochs lasting 4.5s (-1.5/+3.0s). Results showed enhanced prefrontal recruitment with increasing task difficulty in both groups, even before movement onset. Comparing the groups on the same task, non-jugglers showed enhanced activation of prefrontal regions before and during the task execution, whereas jugglers showed enhanced activity in motor-related regions. The results provide a clear indication of practice-induced brain efficiency during the performance of complex bimanual coordinative skills.