Human hand preference: Structural/functional MRI studies
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Description
While one of the most obvious behavioral asymmetries in humans is hand preference, the relationship between degree of handedness, size of the hand representation, and degree of functional activation in sensorimotor cortex between right (RH) and left handers (LH) has not been well studied. In Experiment 1, using volumetric MRI, the surface area (cm2) of the anterior bank of the central sulcus (MI), motor knob (MK), and the posterior bank of the central sulcus (SI) was measured in 20 RH and 20 LH men and women matched for age and education. A significant Sex x Hemisphere x Writing Hand interaction was detected for MI, MK, and SI (all p < 0.05). In RHs, men had a leftward asymmetry while women showed an unexpected rightward asymmetry. For LHs, men had a rightward asymmetry while women had a leftward asymmetry. There was no significant relationship between degree of handedness and surface area of MI, MK, and SI In Experiments 2 and 3, using a different sample of subjects, the surface area of MI, MK, and SI was measured in 9 RH and 8 LH males. Using fMRI, activation was measured during simple motor (air piano), active somatosensory (finger tapping), and passive somatosensory tasks (von Frey). There was a significant main effect of Hemisphere on Surface Area for MI and SI (all p < 0.05), but not for MK (p > 0.05) with MI and SI larger in the right hemisphere across handedness groups. For all tasks, there was a significant main effect of Function on Hand Used for RH and LH (all p < 0.01) where the largest activation was in the contralateral hemisphere regardless of hand used. There was a significant 2-way Writing Hand by Function interaction (all p < 0.01) for air piano and finger tapping where the largest activation was in the contralateral hemisphere across handedness groups, but in this contralateral hemisphere, LH had more activation than RH. There were significant findings relating degree of handedness, surface area of SI, and degree of activation for finger tapping and von Frey which suggested that as degree of handedness decreased, and surface area of SI increased, degree of functional activation increased