Frontal cortical activity during dominant and non-dominant handwriting in healthy adults: an fNIRS study.

Handwriting integrates linguistic and motor processes and is a complex neuropsychological function. We investigated whether frontal cortical activity during written object naming differs between dominant- and non-dominant-hand writing. Sixteen healthy right-handed adults performed written-naming and circle-drawing motor-control tasks with the dominant right and non-dominant left hands while measuring bilateral frontal cortical hemodynamic responses using functional near-infrared spectroscopy. Writing-related activity was defined as the difference in oxygenated hemoglobin responses between written naming and corresponding motor-control conditions. Three-factor repeated-measures ANOVA showed a significant main effect of Hemisphere, with greater written-naming-minus-motor-control responses in the left than in the right hemisphere (F(1, 15) = 11.87, Holm-adjusted p = .025, ηp2 = .442). Hand showed no significant main or interaction effects. Writing duration was longer with the non-dominant hand (t(15) = 3.56, p = .0028, Cohen's dz = 0.89), whereas writing onset latency did not differ significantly between hands. These findings indicate an overall left-lateralized pattern of frontal activity associated with written naming across both hand conditions. However, the absence of significant Hand-related effects should not be interpreted as evidence of equivalent frontal responses between dominant- and non-dominant-hand writing. The findings provide a healthy-adult reference for future studies of compensatory writing following dominant-hand impairment.