Hand preference and magnetic resonance imaging asymmetries of the central sulcus

Hand preference is perhaps the most evident behavioral asymmetry observed i n humans. Anatomic brain asymmetries that may be associated with hand prefe rence have not been extensively studied, and no clear relationship between asymmetries of the motor system and hand preference have been established. Therefore, using volumetric magnetic resonance imaging methodologies, the s urface area of the hand representation was measured along the length of the central sulcus in 15 consistent right- and 15 left-handers matched for age and gender. There was a significant leftward asymmetry of the motor hand a rea of the precentral gyrus in the right-handers, but no directional asymme try was found in the left-handers. When asymmetry quotients were computed t o determine the distribution of interhemispheric asymmetries, the left moto r bank was greater than the right motor bank in 9 of 15 right-handers, the right motor bank was greater than the left motor bank in 3 of 15 right-hand ers, and the motor banks were equal in 3 of 15 right-handers. In contrast, among left-handers, the left motor bank was greater than the right motor ba nk in 5 of 15, the right motor bank was greater than the left motor bank in 5 of 15, and the motor banks were equal in 5 of 15. Although no direct mea sure of motor dexterity and skill was performed, these data suggest that an atomic asymmetries of the motor hand area may be related to hand preference because of the differences in right-handers and left-handers. Furthermore, the predominant leftward asymmetry in right-handers and the random distrib ution of asymmetries in the left-handers support Annett's right-shift theor y. It is unclear, however, whether these asymmetries are the result of pref erential hand use or are a reflection of a biologic preference to use one l imb over the other.