Neural mechanisms of handedness for precision drawing: hand-dependent engagement of cortical networks for bimanual control and tool use
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The neural mechanisms of handedness remain poorly understood, particularly for lateralized movements such as precision drawing. Using functional magnetic resonance imaging (fMRI), we examined how healthy adults and individuals with peripheral nerve injury (PNI) in their dominant hand performed a visually guided drawing task with each hand. We hypothesized that the left superior parietal lobule (SPL) supports drawing with either hand, and that individuals with PNI would recruit the same mechanisms as healthy adults.
Methods
33 Right-handed adults (23 healthy adults, 10 patients) underwent fMRI while performing a precision drawing task, alternating between the right hand (RH) and left hand (LH). LH>RH effects were examined across 20 regions of interest (12 a priori, 8 post hoc) using two approaches: (1) BOLD magnitude, and (2) functional connectivity (FC) modulation, assessed via generalized psychophysiological interaction.
Results
All effects describe LH drawing > RH drawing. Right primary motor cortex (M1) had lower magnitude and greater FC with two networks, both of which exhibited equal-or-greater magnitude: a left hemisphere M1-dorsal premotor circuit, and an intrahemispheric parieto-temporal circuit. Right M1 (also had reduced interhemispheric FC with inferior parietal lobule, which exhibited lower magnitude. Patient group had no effect on magnitude or FC.
Conclusions
Three neural mechanisms differentiate LH from RH drawing in right handed adults. First, a left hemisphere system for bimanual control, which engages intrahemispherically (directly) during RH drawing but interhemispherically (indirectly) during LH drawing. Second, LH drawing increases engagement of a contralateral system that may reflect increased task demands. Third, RH drawing increases engagement of an interhemispheric circuit for tool use. The first and third systems may explain performance asymmetries associated with handedness. Patients with PNI use the same mechanisms as healthy adults, highlighting these mechanisms’ potential as a neuromodulatory target to enhance LH performance after RH impairment.
