Spontaneously emerging patterns in human motor cortex code for somatotopic specific movements

Spontaneous brain activity, which recapitulates stimulus-evoked patterns, may serve as internal priors for tasks. However, its functional-anatomical organization remains unclear. This study investigated whether spontaneous brain activity in the motor cortex is organized somatotopically. Using fMRI, we compared multi-voxel activity patterns during rest within effector-specific motor sub-regions (hand, foot, and mouth) with those evoked by specific movements (finger tapping, toe squeezing, and tongue movements). The results showed that spontaneous activity in each sub-region exhibited greater similarity to task patterns of its corresponding movement than to non-preferred ones. Furthermore, a positive correlation between similarity and the magnitude of the evoked response within each region emerged for the region's preferred movement, while significant negative correlations were found for non-preferred movements. These findings reveal that spontaneous activity in the human motor cortex is somatotopically organized, representing effector-specific functional priors, thus highlighting a structured rest-task relationship.