The effect of handedness on the shape of the central sulcus.

Sinistrals differ from dextrals in the size of certain cortical folds. For instance, handedness has an impact on central sulcus surface area: the sulcus is larger in the dominant left hemisphere of dextrals and vice versa for sinistrals. However, the impact of handedness on the shape of the central sulcus is largely unexplored. In this paper, we propose first an original strategy based on manifold learning to quantify the shape of the central sulcus. Using this approach we show that the "hand knob", a major landmark of the hand motor representation, is sited more dorsally in the left hemisphere in dextrals than in sinistrals. Sinistrals forced to write with their non-preferred right hand display a pattern of central sulcus size asymmetry which is typical of dextrals, yet forced dextrality does not shift the handedness-specific location of the "hand knob". Hence, cortical morphology in adults holds an accumulated record of both innate biases and early developmental experience. Characterizing normal variation of cortical morphology provides a means of systematically correlating behavior with cortical development.