Functional properties of the handwriting brain network: Effects of motor sequence and spatial adaptation constraints.

Writing by hand involves a sequential component, characterized by the succession of strokes to form letters, and a motor adaptation component for controlling pen movements under spatial constraints. The topography of the brain network supporting handwriting is well established, but the functional properties of its components in the motor control of handwriting as a procedural skill remain poorly understood. To address this question, we recorded the brain activity of adult participants as they wrote in the MRI scanner. We manipulated the sequential component of handwriting, e.g., the succession of strokes, and the motor adaptation component, e.g., the visuo-spatial control of pen movements to manage spatial constraints. Analysis of the brain data revealed the recruitment of two distinct networks, depending on the component being manipulated. The motor adaptation component relies on the cortico-cerebellar loop. The sequential component of handwriting rather appears to be computed in both the cortico-striatal and cortico-cerebellar loops. Finally, our study specifies the functional contributions of several regions of the cortical motor system as a function of the sequential and spatial adaptation requirements of the writing movement.