Master of Science
The ability to prepare future action while controlling the ongoing execution is a fundamental characteristic of complex sequential behavior. Recent evidence suggests that when movement preparation and execution are separated in time, brain activity patterns for preparation are highly correlated with those underlying execution. But what happens when the brain needs to prepare and execute movements at the same time, as in the context of rapid movement sequences? We designed a 7T functional magnetic resonance imaging experiment with conditions where the next response preparation either overlapped with the current response execution or did not. Although overlap and non-overlap conditions were matched in all basic perceptual and motor processes, we observed significantly higher activation in the parietal and occipital regions during the overlap condition. The difference between these two conditions was the same, whether the required movement was a simple finger press or a more complex three-finger chord. This suggests that the extra activity was due to the overlap between concurrent execution with action selection but not motor planning, which we found to be more time-consuming for the chord than for the simple finger press. We also did not find significant differences between overlap and non-overlap conditions in the dorsal premotor cortex (PMd), a region traditionally associated with motor planning, even though control analysis showed that it was heavily engaged during motor planning. Our results, therefore, support the hypothesis that motor planning, but not action selection, can run in parallel to ongoing execution with very little need for extra brain activity.
Summary for Lay Audience
Before we start any motor action, our brain needs to go through a preparation phase aiming to bring our motor system into a state of readiness from which our action can unfold. Most of our daily behavior consists of movement sequences. In this context, our brain needs to prepare the future movements while it is busy controlling the ongoing execution. This ability to multi-task appears to be essential for skillful performance of movement sequences such as playing piano. Nonetheless, it is currently unknown how the brain achieves the simultaneous preparation of future actions during the execution of current ones. In our study, we show that the posterior parietal cortex becomes increasingly engaged when preparation and execution need to be done at the same time. The anatomical location of this activity, and its independence of motor complexity suggest that the extra cost arises at the level of action selection, but not at the level of motor planning.
Shahbazi, Mahdiyar, "Neural correlates of online movement preparation" (2023). Electronic Thesis and Dissertation Repository. 9158.