Non-invasive assessment of language dominance with near-infrared spectroscopic mapping

Hemispheric dominance for language is usually assessed by means of the Wada test where amobarbital is injected into the carotid artery. Recently, positron emission tomography and functional MRI have been used as non-invasive alternatives to this method. We have applied 24-channel near-infrared spectroscopic topography (NIRS) as another non-invasive method to detect the unilateral cerebral activation during a language task. We used 11 healthy volunteers and six patients with intractable epilepsy. A word-generation task was applied for 17 s, followed by an extinction/resting period of 60 s. In healthy volunteers, the inferior frontal region was activated on the side opposite to the subject's handedness in infancy. In the epilepsy cases, the activated side agreed with the dominance determined by the Wada test. Our results demonstrate that NIRS is a feasible non-invasive alternative to the Wada test.