Shared neural representation between motor execution and kinesthetic imagery in the primary motor cortex

Although motor imagery activates higher-order motor-related areas, the role of the primary motor cortex (M1) in motor imagery remains unclear. This study aimed to investigate whether motor imagery recruits a neural representation of fingers similar to that of motor execution in the hand M1. Ten healthy right-handed adults executed and kinesthetically imagined tapping using one of four fingers. Using functional magnetic resonance imaging with multi-voxel pattern analysis, we trained the decoder to classify which finger the participants were moving using brain activation during motor execution and tested whether it could predict which finger the participants were imaging to move during motor imagery (cross-classification). We also performed the classification in the reverse direction. The average accuracy of these cross-classifications (mean = 32.71%, SD = 8.31) was significantly higher than chance in the left hemisphere hand M1 (hand-M1). Analysis of the representational geometry showed that the distance of neural representations for the same fingers was statistically shorter than that for different fingers between motor execution and imagery. Furthermore, we conducted a replication study with 14 participants and found results similar to those of the original study (mean cross-classification accuracy = 37.5%, SD = 7.18). Our results suggest that the neural representation of kinesthetic motor imagery is partially similar, but not equivalent, to that of motor execution in the contralateral hand M1.