Neural mechanisms of handedness for precision drawing: hand-dependent engagement of cortical networks for bimanual control and tool use

Neural mechanisms underlying handedness remain poorly understood. We used functional magnetic resonance imaging (fMRI) to study performance of a visually guided drawing task with each hand. We hypothesized that the left superior parietal lobule supports drawing with either hand, and individuals with chroninc peripheral nerve injury (PNI) to the dominant hand use the same mechanism as healthy adults. Methods33 right-handed adults (23 healthy, 10 patients) underwent fMRI while performing a precision drawing task, alternating between the right hand (RH) and left hand (LH). 20 regions of interest (12 a priori and 8 post-hoc) were examined for LH>RH effects on BOLD magnitude and on functional connectivity (FC) modulation via generalized psychophysiological interaction. ResultsDuring LH drawing, contralateral primary motor cortex (M1) had lower magnitude, and greater FC with two networks of equal-or-greater magnitude: left M1-dorsal premotor, and intrahemispheric parieto-temporal network. Contralateral M1 also had reduced interhemispheric FC with inferior parietal lobule, which exhibited lower magnitude. Patient group did not interact with these effects. ConclusionsThree neural mechanisms differentiate LH from RH drawing. First, a left hemisphere bimanual control network engages intrahemispherically (directly) during RH drawing and interhemispherically (indirectly) during LH drawing. Second, LH drawing increases engagement of a contralateral network that may reflect increased task demands. Third, RH drawing increases engagement of an interhemispheric tool use network. The first and third networks may explain the dominant hands performance advantages. PNI patients use the same mechanisms, highlighting their potential as a neuromodulatory target to enhance LH performance after RH impairment.