Neuroscience of cursive handwriting: A computational appraoch

Based on the minimum torque change model (MTCM), Wada and Kawato (1995) proposed a computational model of cursive handwriting which includes the following assumptions. The brain represents via-points that the hand passes through in a trajectory. Cursive handwriting consists of consecutive reaching movements. The via-points for handwriting are retrieved from memory during actual handwriting. Mathematically extracted via-points based on MTCM proved to be practically identical to motor primitives measured by EMG suggesting that drastic directional changes in muscle movement may be determining the location of via-points. Based on computational model, we examined the via-points in the cursive handwriting of a patient with parietal lobe involvement accompaning agraphia. While the control subject showed basically the same numbers and locations in via-points regardless of the velocity of hand movement, the patient's number and locations of via-points differed depending on the velocity of hand movement. The results suggest that the control subject retrieved necessary via-points based on the velocity of handwriting. The results also may reflect the neuropsychological nature of agraphic hand writing in a patient with parietal lobe damage.