FUNCTIONAL ACTIVATION IN MOTOR CORTEX REFLECTS THE DIRECTION AND THE DEGREE OF HANDEDNESS

Handedness is the dearest example of behavioral lateralization in huma ns. It is not known whether the obvious asymmetry manifested by hand p reference is associated with similar asymmetry in brain activation dur ing movement. We examined the functional activation in cortical motor areas during movement of the dominant and nondominant hand in groups o f right-handed and left-handed subjects and found that use of the domi nant hand was associated with a greater volume of activation in the co ntralateral motor cortex. Furthermore, there was a separate relation b etween the degree of handedness and the extent of functional lateraliz ation in the motor cortex. The patterns of functional activation assoc iated with the direction and degree of handedness suggest that these a spects are independent and are coded separately in the brain.