While one of the most blatant human asymmetries is the preference for one hand over the other for skilled movements such as writing, it is unclear whether the neural substrates that mediate unimanual hand preference differ in right and left handers. The motor hand representation has been localized along the anterior bank of the central sulcus. Even though anatomical studies, including MRI and postmortem, have found that anatomical asymmetries of this area differ in right and left handers, very few studies have used a consistently large sample size (N greater than 15) with equal numbers of right and left handed males and females. To our knowledge, there are no studies that have looked at the precise anatomy, function, and behavior of hand preference in left and right handers. In Experiment 1, structural MRI methodologies will be used to investigate a relationship between the anatomy of the motor hand representation and behavioral asymmetries in right and left handed adults. In Experiment 2, functional MRI methodologies will be used to investigate the functional motor hand representation and will compare these functional activations to the anatomical representation and to behavioral measures of handedness. In Experiment 3, structural and functional MRI methodologies will be used to study the somatosensory hand representation in right and left handers. In each experiment, asymmetries will be compared within subjects and between right and left handers. It is hypothesized that the anatomy and function of the motor hand representation will be larger in the left cerebral hemisphere in right handers and will be more variable in left handers, similar to the anatomical asymmetries associated with language function. Similar relationships are expected in the anatomy and function of the somatosensory hand representation. In addition, it is expected that the anatomical and functional asymmetries will be related to behavioral measures of hand reference.
