Slide Slam G6
Development of the relationship between spelling and motor control of handwriting : a coupled fMRI and kinematics study
Marieke Longcamp1, Palmis Sarah1, Fabiani Elie1, Danna Jeremy1, Habib Michel1, Kandel Sonia2, Anton Jean-Luc1, Nazarian Bruno1, Sein Julien1, Mahieu Anne1; 1Aix-Marseille University and CNRS, 2GIPSA Lab, Grenoble University
Recent research in adults demonstrated that processes underlying the orthographic and motor aspects of handwriting occur in parallel, and that orthographic processes influence motor processes. Here, we examined how this relationship evolves between middle-childhood and adulthood both at the behavioral and at the brain level. In the light of recent behavioral studies, we hypothesized that orthographic and motor processes occur in a more sequential and independent fashion in children, whose writing is not yet automatized. We designed an experiment where we coupled functional magnetic resonance imaging (3-Tesla MRI Scanner Magnetom-Prisma, Siemens, Erlangen, Germany; EPI sequence with TR= 957 ms, TE= 30 ms, voxel size= 2.5 mm3, multiband factor= 4, slices= 56) and kinematic recordings (MRI-compatible digitizing tablet) during a writing to dictation task (single regular and irregular french words, cursive or semicursive writing). We compared three groups of participants: 3rd grade children (8-9 years old, N = 18), 5th grade children (10-11 years old, N = 24), and adults (N = 26). We found an increase of writing duration and size for irregular compared to regular words in all 3 groups. This effect of regularity on writing was stronger for 5th grade children than for the other 2 groups. It is assumed to be a marker of the influence of spelling retrieval on motor processes. At the brain level, we computed statistical models that integrated the single trial behavioral data to target main effects of irregularity during handwriting execution. We evidenced stronger responses to irregular words in a distributed network including inferior frontal and ventral occipitotemporal regions known for their systematic recruitment for orthographic processing, and dorsal premotor and parietal regions known for their functional specificity to writing movements. This pattern of activation replicates previous findings. Together with the behavioral data, it suggests that spelling processes are active during the execution of handwriting and influence motor control in both adults and children. However, we also observed a more prefrontal distribution of irregularity processing in 5th graders, and a specific recruitment of the anterior cingulate cortex and caudate nucleus for irregular words in this age-group. Both regions belong to a network crucial for conflict monitoring and inhibition. Our results indicate that contrary to our expectations, children are able to process orthographic and motor information in parallel during writing. However, they also suggest that the relationship between orthographic and motor processes matures between 3rd grade and adulthood under the influence of domain-general prefrontal control mechanisms, with a crucial developmental window at age 10-11. These data contribute to our understanding of how writing skills become grounded in the brain.