The brain puts an enormous amount of resources into the ability to speak and understand speech. These resources have to contend with managing information about thousands of words and the construction of syntax combined with the structures that allow kids to recognize sounds and move their mouths to speak. However, sometimes there are problems that occur in these areas of the brain, and this can cause difficulties in the ability to learn to read.
The language system of the brain is a complex set of structures that facilitates several abilities, including the power to speak, read, write and acquire new information. It's governed by a network of neurons, which are specialized brain cells that produce thoughts and feelings. This network occurs in the two cerebral hemispheres of the brain, comprising mainly the cortex and the white matter. The white matter contains billions of fibers that provide connections among different areas of the cortex. These relationships are integral to language, but the way in which they occur is still relatively unknown.
The two halves of the brain are not precisely homologous to each other. The term "brain lateralization" is used to refer to this phenomenon. Each hemisphere has functional specializations whose neural mechanisms are located in a specific half of the brain. Speech and language ability are particularly specialized. In the 19th century, both Paul Broca, a French neurosurgeon, and German neurologist Carl Wernicke identified areas in the left hemisphere of the brain that govern language.
It is a common scientific aphorism that left-handed people use the right sides of their brains to process language. However, about 70 percent of left handers still use the left side of their brain compared with nearly 95 percent of right-handed individuals. This may be because the left hemisphere works faster, and timing is absolutely integral to the proper formation of words and sounds and the understanding of grammatical rules. The remaining 30 percent of left-handed individuals have right hemisphere or symmetrical language processes.
According to Professor of Psychology and Medical Education Chris McManus, author of the book "Right Hand, Left Hand" from the University College London, the genes that determine handedness also govern development of the brain's language centers. This link has led some scientists to theorize that there could be a link between handedness and language-related disorders.
A 2010 study published by the journal "Human Molecular Genetics" by researchers from the University of Oxford found a relationship between a variant of a gene called PCSK6 and relative hand skill in children with reading difficulties. Those who carried the variants were much more skilled with one hand compared with the other than those who did not have the variant; in other words, they greatly favored one hand. The protein produced by PCSK6 is known to interact with another protein called NODAL, which plays a key role in establishing left-right asymmetry early in embryonic development.
Handedness itself does not dictate the efficacy of the development of language ability. In many aspects, right and left handers may be quite similar. However, statistics show that left handers are more likely to develop learning disabilities such as dyslexia in their youth in addition to many other disorders. Left handers, especially those who demonstrate a strong proclivity for the left hand, are more likely to have anomalous or unique brain anatomy that differs from the usual left brain language dominance, so they tend to be at a greater risk for disturbances of normal functions.