Convergence, degeneracy and control.

Understanding the neural representation and control of language in normal bilingual speakers provides insights into the factors that constrain the acquisition of another language, insights into the nature of language expertise and an understanding of the brain as an adaptive system. We illustrate both functional and structural brain changes associated with acquiring other languages and discuss the value of neuroimaging data in identifying individual differences and different phenotypes. Understanding normal variety is vital too if we are to understand the consequences of brain-damage in bilingual and polyglot speakers.