Functional Brain Asymmetry and Individual Differences in Hand Preference in Early Ontogeny

This work was aimed at studying the brain mechanisms of hand preference in 10- to 11-month-old infants. According to the results of neuropsychological investigations, the preference for the right hand in children of this age (at the populational level) primarily arises in actions that demand involvement of the functions of planning and motor control of reaching (functions of the motor control of reaching: FMCR) for an object. The stage of development of the FMCR in each child was scored on the Diamond scale. Total numbers of movements performed by the right and left hands and a coefficient of the manual asymmetry (AC) were calculated. On the basis of quartile analysis of the AC distribution, groups of right-handers, left-handers, and ambidextrals were formed. The EEG was recorded in the state of visual focused attention, and the spectral absolute amplitude density (AAD) of the sensorimotor rhythm and other infant EEG rhythms in the frequency band was analyzed. In order to estimate the statistical correlation of manual asymmetry, gender, and stage of development of the FMCR with functional asymmetry of the AAD of the -band rhythms in different cortical derivations, analysis of variance with factors of repeated measurements and analysis of multiple regression were used. The main results showed that 10- to 11-month-old children with different types of manual asymmetry differed in interhemispheric asymmetry of the visual attention-related EEG -band rhythms (including asymmetry of the sensorimotor rhythm). The maximum differences were observed in the lateral frontal and posterotemporal areas of the brain cortex. The leftward amplitude asymmetry was characteristic of right-handers; in left-handers and ambidextrals, the EEG amplitude was distributed over the brain hemispheres in a more symmetric way. The correlation between the brain and manual asymmetries was stronger in boys than in girls. There was a strict linear correlation between the degree of manual asymmetry and interhemispheric asymmetry of the EEG sensorimotor rhythm in the precentral and lateral frontal brain areas. On the whole, the close correlation of the manual asymmetry with functional asymmetry of the EEG sensorimotor rhythm suggests that it is determined by the formation of the brain FMCR lateralization.