Contributions of the right and left brains to manual asymmetry in hand skill in right-handed normal subjects.

The relation of intermanual difference in hand skill to cerebral lateralization was studied in right-handed male and female subjects. Hand preference was assessed by the Edinburgh Handedness Inventory. Hand skill was measured by the peg moving task. In subjects with familial sinistrality (FS+), the mean right hand peg moving times (PMTs) were found to be significantly and negatively linearly correlated with the mean left minus right (L - R) hand PMTs in females (no correlation in males). Contrarily, there was a direct relationship between the mean L - R hand PMTs and the mean left hand PMTs in FS+ males (no correlation in FS+ females). Similar results were obtained with the FS- subjects. The correlations were modified by eye and foot preferences. The overall results suggested that generally the right brain in males and the left brain in females are of importance in determining the intermanual difference in hand skill; an insufficient right brain (a slower left hand) in males and a sufficient left brain (a faster right hand) in females would create a more asymmetrical organization in skill between hands.