Correlations between hand preference and cortical thickness in the secondary somatosensory (SII) cortex of the common marmoset, Callithrix jacchus.

Cortical asymmetries are well established in humans for language and motor regions and correlate with handedness. Here the authors investigate structural differences in the hemispheres of left- and right-handed common marmosets using surface photography and histology. The hand preferences of 11 marmosets were assessed over their adult life span using a simple reaching task. A significant correlation was found between the length of the right lateral sulcus/brain weight and the % right-hand preference (r = .86, p = .001). Cortical thickness on the superior bank of the right lateral sulcus posteriorly was also positively correlated with % right-hand preference (r = .69, p = .025). Comparison of this site with previously published functional maps of the marmoset cortex show this area corresponds to SII, a region involved in tactile processing and somatosensory discriminations. It is suggested that the correlation between SII thickness and right-hand preference would be consistent with the fact that right-handed marmosets are more proactive than left-handers in exploring novel objects by touch. Enlargement of a cortical area involved tactile discriminations could be a precursor to the evolution of right-handedness as a population bias.