An update on determination of language dominance in screening for epilepsy surgery: the Wada test and newer noninvasive alternatives

The intracarotid amobarbital procedure or Wada test has been the gold standard for lateralization of language dominance before epilepsy surgery. It is based on deactivation of language cortex with intracarotid anesthesia. However, it is an invasive test with risks and discomforts, and it also has limitations. There has been great interest in replacing the Wada test with a noninvasive procedure. One alternative, repetitive magnetic stimulation works by deactivating language cortex, but most other promising alternatives are based on brain activation. Functional magnetic resonance imaging (fMRI), 15O-water positron emission tomography, single photon emission computerized tomography, transcranial Doppler, and near infrared spectroscopy detect hemodynamic responses to language cortex activation, while magnetoencephalography more directly measures event-related physiological activation. Some of the techniques also provide localization of language functions, whereas the Wada test is strictly a lateralization method. Based on widespread availability, fMRI will likely be the most widely used alternative.