The surface area of the central sulcus has been found to be larger in the dominant hemisphere, as well as the 'hand knob', an area in the primary motor cortex which is responsible for hand movements, is located more dorsally in the left hemisphere of people who are right- compared to left-handed[11] Marian Annett devised the Right Shift Theory in 1972, which states that language areas and motor cortex development is preferential in the left hemisphere due to the theoretical gene RS+.
The presence of the RS+ gene promotes left-hemispheric dominance, in turn introducing a right-handedness bias which shifts the curve towards the right.
[13] The corticospinal tract is a bundle of white matter which connects the cerebral cortex with motor neurons in the spinal cord.
Left-handers who were forced during childhood to use their right hand showed a larger surface area of the central sulcus in their left hemisphere, which is associated with right-handedness.
Also, structures in the basal ganglia such as the putamen also mirrored developmental right-hand dominant individuals in the forced group.
A number of asymmetrical findings have been disputed, with various studies stating null results in opposition to previously reported differences.
[11] This is an issue in handedness neuroscience, as imaging methods are highly susceptible to type 1 errors due to the number of comparisons which they make.
Clearly, advances in research are still necessary to unveil true causal relationships between structural differences and their manifestation in the form of handedness.