The mystery of left lateralization09 Mar 2011
This morning, a timely post by cognitive neuroscientist Sophie Scott addresses the localization of language functions on the left side of the brain:
The elephant in the room is why linguistic representations and processes are so associated with the brains left hemisphere in the first place. The left lateralisation of language is seen in 96 per cent of right-handed people, and is still there in 73 per cent of left-handed people (Knecht et al, 2000). It is there for men and women equally. People whose language centres are not in their left hemisphere have it in their right hemisphere: there is no evidence for people who have an intermediate, more equally divided representation of language across the left and right sides of the brain. And if the language-dominant hemisphere is damaged, the non-dominant hemisphere can take over function. Does this mean that the non-dominant hemisphere still performs linguistic functions in some low-key way? Or that it can adapt following damage to the brain (or perhaps even that it is released from some form of suppression)?
I discussed this to some extent last week (“Language bootstrapping the brain”), but it’s worth re-emphasizing: the great plasticity of language localization is really not very compatible with the hypothesis of a “language organ”, except in the sense that an “organ” might self-organize upon input from the environment. It’s a bit like saying the spleen could spontaneously take on some of the functions of the kidneys, in the right environment.