Methods for determination of language dominance: the Wada test and proposed noninvasive alternatives

The intracarotid amobarbital procedure, also known as the Wada test, helps to lateralize language dominance by deactivating the language cortex with an intracarotid injection of an anesthetic agent. Although it has been the gold standard for determining language dominance for more than four decades, its invasiveness has prompted a search for noninvasive alternatives. Potential replacements have included neuropsychological techniques, measurements of anatomic brain asymmetries, magnetic stimulation for deactivation of language cortex, measurement of the electrical or magnetic neurophysiologic response to language activation, and methods that detect the hemodynamic response to activation of language cortex, namely increased local blood flow or increased local oxygenation. Based on widespread availability and the ability to provide localizing as well as lateralizing information, functional MRI will likely be the most widely used alternative.