Handedness and task demands modulate motor cortex lateralization: A cross-sectional fNIRS study

It is generally accepted that the contralateral cerebral hemisphere is activated during motor control of an upper limb. Most studies exploring the cerebral mechanisms of motor control have focused on right-handed individuals, who represent around 90% of the general population. However, it appears that the lateralization of cortical activation is linked to various factors such as manual preference, the use of the dominant or non-dominant hand, and the type of task performed. The aim of this study was to compare cortical activation asymmetry during two different motor tasks as a function of manual laterality. We included 25 right-handed and 25 left-handed healthy individuals. They performed a distal and a manipulation task with each hand. Cortical activity in the premotor (PMC) and sensorimotor cortices (SMC) was measured using functional near-infrared spectroscopy (fNIRS). A Laterality Index was calculated to assess the degree of left-right hemisphere activation asymmetry for each region of interest. Irrespective of the hand used, cortical activation was predominantly contralateral for right-handers and more bilateral for left-handers. These results were more marked when using the right hand (non-dominant for left-handers) and seem to be modulated by the specific motor demands of the task. Thus, brain organization was less asymmetrical in left-handers than in right-handers, probably because of enhanced interhemispheric connectivity. This organization might favor recovery mechanisms in pathologies such as stroke. These results underline the importance of considering manual laterality in both neurophysiological and clinical studies of central nervous system pathologies.