Asymmetric effective connectivity within frontoparietal motor network underlying motor imagery and motor execution
Both imagery and execution of motor controls consist of interactions within a neuronal network, including frontal motor-related regions and posterior parietal regions. To reveal neural representation in the frontoparietal motor network, two approaches have been proposed thus far: one is decoding of actions/modes related to motor control from the spatial pattern of brain activity; another is to estimate directed functional connectivity, which means a directed association between two brain regions within motor regions. However, directed connectivity among multiple regions of the motor network during motor imagery (MI) or motor execution (ME) has not been investigated. Here, we attempted to characterize the directed functional connectivity within the frontoparietal motor-related networks between the MI and ME conditions. We developed a delayed sequential movement and imagery task to evoke brain activity associated with data under ME and MI via functional magnetic resonance imaging scanning. We applied a causal discovery approach, linear non-Gaussian acyclic causal model, to identify directed functional connectivity among the frontoparietal motor-related brain regions for each condition. We demonstrated higher directed functional connectivity from the contralateral dorsal premotor cortex (dPMC) to the primary motor cortex (M1) in ME than in MI. We mainly identified significant direct effects of the dPMC and ventral premotor cortex (vPMC) to the parietal regions. In particular, connectivity from the dPMC to the superior parietal lobule in the same hemisphere showed significant positive effects across all conditions. Contrastingly, interlateral connectivities from the vPMC to the superior parietal lobule showed significantly negative effects across all conditions. Finally, we found positive effects from A1 to M1 in the same hemisphere, such as the audio-motor pathway. These results indicated that the sources of motor command originated in d/vPMC influenced M1 and parietal regions as achieving ME and MI. Additionally, sequential sounds may functionally facilitate temporal motor processes.