Dissociated neural substrates of motor execution and planning in learning multiple sensorimotor mappings

Previous behavioral studies have shown that human can adapt to multiple sensorimotor mappings simultaneously. Motor planning, rather than motor execution, has been shown to play a crucial role in distinguishing between multiple interfering motor tasks and in forming motor memory. However, it remains unclear how the human brain represents distinct motor planning and execution for multiple sensorimotor mappings. To address this, we designed an fMRI experiment specifically to dissociate motor planning from motor execution during multiple sensorimotor mappings learning. Critically, the design allowed us to compare conditions where participants prepared for different visuomotor rotations but executed identical movements, isolating the neural representation of motor planning. We found that the posterior parietal cortex (PPC), including the superior and inferior parietal lobules, exhibited increased activity during the planning. However, using Multivoxel pattern analysis (MVPA) to look at the representation, we found a dissociation between motor execution and planning. While motor execution could be reliably decoded in the sensorimotor cortex, PPC, and cerebellum, planning-related activity for opposite rotations was not decodable in any region of interest. These results suggest that while the PPC is actively recruited for motor planning, the specific neural patterns differentiating conflicting plans may be less distinct than those for execution.